A Celebration of Insects

It’s a funny world we live in.  We hear regular reports of insect declines in the news and still get bombarded with constant ads for services pitching a mosquito free yard all summer and a grub free lawn.  But what about simply appreciating insects and the critical roles they play in our everyday lives?  

That’s a goal of the first ever Wisconsin Insect Fest being held at the Kemp Natural Resources Station  in Woodruff, Wisconsin later this month.  The two-day event—being held on Friday, July 26th and Saturday, July 27th—is a celebration of insects.

Wisconsin Insect Fest is free, open to the public, and will feature a wide range of activities for insect enthusiasts of all ages.  Topics will range from how to observe and collect insects, to the role of insects in the ecosystem, entomophagy, and even forensic entomology.  The Wisconsin Insect Fest will also feature The Great Wisconsin Bug Hunt—a 24-hour BioBlitz activity to see just how many arthropods can be spotted at the Kemp station in a 24-hour period (including a night time activity in conjunction with National Moth Week).

If you love insects, join in the festivities at the Wisconsin Insect Fest later this month or check out the event website for details: tinyurl.com/WisconsinInsectFest

Black Flies: Out for Blood

Mosquito season has officially kicked off in Wisconsin, meaning the omnipresence of repellents for the foreseeable future.  If mosquitoes have redeeming properties, it’s that they at least serve as food for a wide variety of animals and can even act as pollinators in some cases.  When mosquitoes bite, they do so with surgical precision that would make a phlebotomist green with envy.  Simply reading about mosquitoes might make you want to scratch, although on the spectrum of biting flies, things could be much more sinister…

Also very active at the moment in Wisconsin are black flies (Family Simuliidae) and our state is home to 30 species of these tiny sanguivores.  Black flies—or “buffalo gnats” due to their hump-backed appearance—are deceptive creatures for their small size (~ 1/8″ long).  You usually don’t notice them as much by sound like buzzing mosquitoes, but when they land to feed, these tiny flies are vicious.  Rather than using needle-like mouthparts to delicately probe for blood vessel like mosquitoes, black fly mandibles resemble the jagged edge of Rambo’s survival knife which they use in a “slash-and-slurp” approach.  These mouthparts slice into flesh to create a pool of blood which they then consume.  If this sounds unpleasant—it is!  Reactions to black fly bites can sometimes be severe, with fever and enlargement of nearby lymph nodes.  In addition, their sheer numbers can take a psychological toll and can be a strong test of one’s fortitude if you must be outdoors during peak black fly season.

Adult black fly taking a blood meal. Photo Credit: Credit: D. Sikes, via Flickr.

Of the 30 species in Wisconsin, only a handful actually bite humans.  Other species are “picky eaters” with a strong preference for other animals.  The species, Simulium annulus, specializes on common loons and in “bad” years the constant pestering can force adult loons to abandon their nests.  Other birds, such as purple martins and bluebirds can face high rates of chick mortality when the black flies are bad.  Pets, like dogs can commonly get bites and large pinkish welts on the soft skin of their belly.  Dairy cows can be harassed to the extent that feeding and weight gain is greatly reduced and milk production all but ceases.  In some cases, large animals including deer, cows, and horses have been killed outright by black flies.

With that said, if you’ve ever encountered an outbreak of black flies, you’d likely remember.  If you haven’t bumped into black flies before, you’re perhaps in a good spot on the map.  The larvae of many black fly species tend to be associated with streams and rivers, meaning that geography can play a role with outbreaks.  Within the state, areas near the Wisconsin River and other large rivers and streams tend to see the most intense black fly activity.  Black flies can be even worse to the north.  These insects can be notoriously bad in the Boundary Waters Canoe Area in June, and in Canada black flies have even been enshrined in film and a surprisingly catchy folk song.

Black fly larvae in a river. Photo credit: GlacierNPS via Flickr

If there’s good news about black flies, it’s that the adults are short-lived.  Wisconsin tends to see a blitz of activity spanning a 2-3 weeks in late spring.  When black flies are active, the best approach is to layer up with long sleeves, break out the repellents like DEET, and use a head net if needed.  If you’re in an area with intense black fly activity, cutting back on outdoor activities until these insects run their course for the year may be the simplest option.

What’s Trending? Ticks and Lyme Disease

This month’s post features contributions from Dr. Bieneke Bron


As stories about measles and vaccinations circulate in the news, it’s easy to lose track of other emerging health threats.  May is Lyme Disease Awareness month, and if you want to look at an emerging health threat particularly relevant to the Midwest, look no further than deer ticks and Lyme disease.

Adult female deer tick (Ixodes scapularis). Photo credit: Robert Webster / xpda.com / CC-BY-SA-4.0 via Wikipedia.

A Brief History of Deer Ticks and Lyme Disease:
The Lyme disease story is surprisingly new to Wisconsin and deer ticks are something that our grandparents didn’t have to deal with while growing up.  It wasn’t until the late 1960’s that our first deer ticks were documented in northern Wisconsin. At the time, this particular tick was known from more southern locations, so the first Wisconsin reports were noted as a curiosity in the scientific literature.  In actuality, this marked an early foothold of deer ticks in the region, which have spread rapidly.  Fast forward 50 years and deer ticks are widely distributed around Wisconsin and surrounding states.

Deer ticks are only one component of the Lyme disease equation. The spirochete bacterium Borrelia burgdorferi (or the closely-related B. mayonii) must be transmitted by these ticks to cause Lyme disease in humans.  Similar to the deer tick situation, Lyme disease has had an interesting recent history.  Research from the Yale School of Public Health suggests an ancient origin of Borrelia burgdorferi, but the first clinical cases of Lyme disease weren’t formally documented in the medical literature until the 1970’s.  At that time, an unusual cluster of juvenile arthritis cases with an accompanying rash helped researchers characterize the disease near Lyme, Connecticut*.  It wasn’t until the early 1980’s that the roles of deer ticks and Borrelia burgdorferi were recognized.

Skip ahead a few decades and the numbers for Lyme disease have increased steadily.  Today Lyme disease is the most commonly reported arthropod-borne disease in the US with over 40,000 confirmed and probable cases in 2017 alone.  Looking at Wisconsin’s statewide averages, approximately 20% of deer tick nymphs (juveniles) and 40% of adult deer ticks are carrying Lyme disease, which are alarmingly high percentages.

Deer tick nymphs (juveniles) next to chia seeds, sesame seeds, flax seeds and a penny for size reference. Photo Credit: Dr. Bieneke Bron, MCE-VBD.

Tracking Ticks with Mobile Technology:
With the changing tick and tick-borne disease situation over the last 50 years, understanding the factors that influence where and when ticks are encountered is more important than ever before.  Researchers at the Midwest Center of Excellence for Vector-Borne Disease and the Northeast Regional Center for Excellence in Vector-Borne Diseases have teamed up to develop The Tick App—a mobile app to help gather critical clues to better understand human exposure to ticks.  The app, available in iTunes and GooglePlay, not only allows the public to contribute valuable data to tick researchers, but the app provides helpful tips on tick identification, activity, and precautions to take.  During the tick season, the researchers will also identify ticks from the images submitted in the app.

As we move into peak tick season, Midwesterners should be aware of ticks and take appropriate precautions to protect themselves [Recommended reading: the ABCs of Tick Season].  Learn more about The Tick App by visiting thetickapp.org or follow on Twitter @TickAppOnTour.


*Interestingly, a 57-year old physician from Medford, Wisconsin, was diagnosed with the hallmark rash of Lyme disease (erythema migrans) in 1969 [Scrimenti 1970, Arch Derm].  Just imagine, Lyme disease being known as Medford disease…

Identifying Insects by Smell, Part 2: Odorous House Ants

When it comes to ants at the UW Insect Diagnostic Lab, the top species seen at the lab include carpenter ants (Camponotus spp.), pavement ants (Tetramorium immigrans), and odorous house ants (Tapinoma sessile).  Odorous house ants were the most commonly reported ants at the lab in 2018, possibly due to the rainy conditions which can force these ants indoors in their search for food.

Odorous House Ant. The single flattened node is hidden under the gaster. Photo credit: April Nobile, specimen: CASENT0005329, from www.antweb.org.

Identifying ants by sight and smell
The tiny brownish odorous house ant measures in at only an eighth of an inch long, but a few features allow for quick identification.  Ants are generally broken into two main groups depending on the numbers of bumps or “nodes” in their constricted waist.  Odorous house ants are considered “one node” ants, although their single node is flattened and is hidden from view by the gaster (sometimes mistakenly referred to as the “abdomen” of ants).  This is strikingly different than other ants, such as carpenter ants or field ants, where the single upright node can even be visible to the naked eye.  This flattened node of odorous house ants is a key identifying feature but does require magnification to interpret this trait.

Carpenter ant—note the visible node or “bump” in the narrow waist. Photo Credit: Judy Gallagher, via Wikipedia.

Interestingly, the easiest way to identify these ants isn’t by sight, but by smell.  Identifying insects by smell may sound odd, but can be a quick and dirty way to confirm the identity of this ant species, and a few other ants like citronella ants.  When squished, odorous house ants have an odor reminiscent of coconut, although some say rotting coconut or even blue cheese.  This scent fades with older, dried-out specimens but is usually quite noticeable in fresh ants.

Country ant, city ant:
Odorous house ant colonies occur both indoors and outdoors in the Midwest, but the overall location of these ants in the landscape can have a drastic influence on colony structure and behavior.  In natural areas (such as forests), odorous house ant colonies tend to be small (often <100 workers) and the ants are generally “well behaved”.  In urban areas, these ants can produce much larger populations with multiple queens, tens of thousands of workers and many different nesting sites. They can behave like an invasive species in such situations.

When it comes to their nesting habits, odorous house ants don’t produce mounds like other common ants.  Instead, these ants are fond of preexisting cavities—small hollow voids beneath rocks or man-made objects, amongst log piles, fallen leaves, mulch beds, or similar spots.  I’ve even seen them take advantage of the cozy space inside of a fake rock “Hide-a-Key” on several occasions!  Indoors, odorous house ants like to nest in hollow cavities such as wall voids, especially if a moisture source is nearby.  These ants can also easily wander indoors when foraging, making them a common indoor nuisance invader.

SMall black ant—an odorous house ant worker
Odorous House Ant (Tapinoma sessile) worker. Photo Credit: JJ Harrison via Wikipedia

Got dessert?
In addition to their essence-of-coconut scent, odorous house ants are also known for having a notorious sweet tooth.  Ant species vary quite a bit in their food preferences, with certain ants seeming to favor the “keto diet” with a strong preference for proteins or fats.  In contrast, odorous house ants have a particular fondness for carbohydrate-rich materials, such as honeydew from aphids, nectar from plants, or sugary human foods.  As a result, these ants routinely invite themselves to picnics and into kitchens.  However, their sugar-loving ways can also be their Kryptonite and odorous house ants usually respond well to sugar-based baits when they do find their way indoors.

Purple Carrot Seed Moth Appears in Wisconsin

In a given year at the UW Insect Diagnostic Lab, I typically document 2-3  new, non-native, potentially-invasive insects in Wisconsin. In some cases, these species make an appearance only to fade into the background with little impact, while other exotics become heavy-hitting invasive pests (e.g., emerald ash borer and gypsy moth). The latest non-native pest to make an appearance in the state is the tiny “purple carrot seed moth” (Depressaria depressana) and its impacts are not yet fully known. This species has a wide native range and can be found from western Europe through Russia to China.  It was first documented in North America in 2008 and is so new that few images exist and it’s not included in the common caterpillar and moth field guides on the market.

Purple carrot seed moth. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

In the last decade, the purple carrot seed moth has been documented in many locations in southern Canada and the northeastern US and has also been spotted in a few scattered locations in Michigan, Indiana, and Illinois. In mid-July of 2018, two reports came into the UW Insect Diagnostic Lab in rapid succession—Kewaunee and Dodge counties in Wisconsin. These cases were confirmed through images and caterpillar specimens that were reared to adult moths. After discussing the purple carrot seed moth on a recent episode of Wisconsin Public Radio’s The Larry Meiller Show, several additional suspected cases were reported in the state: Racine (Racine Co.), Random Lake (Sheboygan Co.), Burnett (Dodge Co.), and Franklin (Milwaukee Co.).

These insects get their name due to their association with flowers (umbels) of plants in the carrot family (Umbelliferae). The caterpillars of the purple carrot seed moth are small (3/8 inch long when mature), but dozens can feed on a single umbel. The caterpillars are dark green or reddish with many conspicuous white spots on their bodies. In addition to feeding on the flowers, the caterpillars tie together floral parts with silken webbing, which can make herbs like dill unusable. Eventually the caterpillars pupate within the webbing and emerge as adult moths a short time later. The adult moths are 3/8 inch long with a pale patch near the head; their purplish-grey wings are folded back along the body when not flying.

Caterpillar of the purple carrot seed moth, note the many conspicuous white spots on the body. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

The impacts of this non-native insect are not fully known for our area. The reports of plant damage in Wisconsin thus far have only been on dill. Due to the plant parts attacked (flowers), the impact on carrots, celery, and parsnip crops will likely be minor. The biggest impacts would be expected with umbelliferous crops commonly grown for seeds: dill, fennel, and coriander. Luckily, several organic control products may offer help on herbs: insecticidal soap and Neem oil are two low-impact products expected to help control this pest, if needed.  Cutting out and destroying infested flower heads may be another helpful tactic.

Damage from the purple carrot seed moth on dill. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

Because this pest is “new” in Wisconsin, if you believe you’ve found it on dill or other plants from the carrot family, please snap some pictures and contact me to help document this species in the state.

If you’d like to learn more about this insect and its potential impacts check out this video through the Wisconsin First Detector Network.


May 2019 Update: A current distribution of known PCSM sightings can be found below.  If you encounter this insect this summer in Wisconsin, feel free to let me know, so I can better keep track of its activity in the state.        —PJ

County records of the Purple Carrot Seed Moth from 2018. Map Credit: PJ Liesch, UW Insect Diagnostic Lab

Is This a Kissing Bug?

Kissing” and “bugs”—two words you wouldn’t expect to be put together in the same sentence have been strung together rather frequently in the news lately.  No, this isn’t some poorly understood internet phenomenon amongst the youth of the country.  Rather, when you hear about “kissing bugs”, we’re really talking about a group of blood-feeding assassin bugs (Family Reduviidae, Triatoma species).

So what’s the story behind these insects and why the hype?
Kissing bugs are similar to bed bugs as they both feed on the blood of vertebrate hosts.  However, unlike bed bugs which have anthropophilic habits, kissing bugs are typically associated with animal nests in wooded areas.  Kissing bugs don’t go out of their way to sneak indoors, although if they do happen to wander in they can be attracted to the heat and carbon dioxide of a sleeping human.  When human bites do occur, it can often be on the exposed, softer skin of the face, hence the nickname of “kissing bugs”.  The biggest concern with kissing bugs is that under the right conditions they can serve as a vector of American trypanosomiasis (aka Chagas Disease), a serious disease that can lurk in the body and ultimately affect the heart and other organs.

What does the kissing bug story have to do with Wisconsin and the Great Lakes region?
In brief: not a whole lot.  While there are nearly a dozen species of kissing bugs in the western hemisphere, these insects are primarily found in rural Central and South America.  I recently spent some time amongst the Wisconsin Insect Research Collection’s  8 million+ specimens, and found no verified cases of kissing bugs in Wisconsin.  Technically, these insects have been found in some of the southern states, although they tend to be quite rare in the US and there isn’t any evidence to suggest that they’re expanding their range or increasing their numbers.  Unless you’ll be spending an extended amount of time in Central or South America, the threat posed by kissing bugs and Chagas disease is basically non-existent.  Overall, the hype about kissing bugs is more bark than. . .bite.

Think you’ve found a kissing bug in Wisconsin (or elsewhere)?
There are a few look-alikes that could potentially be confused with kissing bugs.  Boxelder bugs (Boisea trivittata) share the red and blackish coloration of certain kissing bugs, while the masked hunter assassin bug (Reduvius personatus) shares a similar body size and shape.  However, due to the slender body and similar “checkerboard-like” pattern around the abdomen , the insect getting confused the most with kissing bugs at the moment seems to be the western conifer seed bug (Leptoglossus occidentalis), which can be very common in Wisconsin and in many parts of the country.

Why the western conifer seed bug?  As described in an earlier post, western conifer seed bugs frequently try to sneak indoors in the fall to seek out a sheltered spot to spend the winter.  As a result, encounters with these harmless insects occur on a regular basis.  Want some peace of mind that the insect you’ve seen is a western conifer seed bug and not a kissing bug?  Check out this handy side-by-side guide comparing the eastern conenose kissing bug (Triatoma sanguisuga) with the western conifer seed bug:

Is this a kissing bug?
Distinguishing features of the Eastern Conenose Kissing Bug and Western Conifer Seed Bug; click for larger version. Photo Credit: PJ Liesch, UW-Entomology

Further reading:
Gwen Pearson recently covered the Kissing Bug story for Wired and included some excellent references.

Spring’s Coming…and so are the Insects

With daylight saving time beginning over the weekend and warmer temperatures knocking at our door, spring is finally crawling our way.  Last winter is one we won’t soon forget—the season started out mild before temperatures plummeted with January’s polar vortex.  During the coldest stretch, our coping strategy might have involved layers of blankets and reruns on Netflix, but what about the bugs? Questions regarding the winter impacts on insects have been some of the commonest at the UW Insect Diagnostic Lab this year.  There will undoubtedly be some impacts of this year’s polar vortex, although many insect species are well-equipped to deal with the cold.  Before we know it, overwintering insects will become active again in the Midwest and many species will simply shrug off the polar vortex as if it hadn’t happened.  For insects that didn’t fare as well in the cold, high reproductive capacities will likely allow their numbers to bounce back relatively quickly.

Thus, 2019 isn’t going to be insect-free by any means and intuitively this makes sense.  We know that every year insects make it through the winter months and become active as temperatures creep up in spring.  Looking at an evolutionary time scale, this year’s cold snap wasn’t the first time that the species in our area have encountered frigid temperatures before, and many creatures are adapted to survive surprisingly cold conditions.   We might have chosen to block it out of memory, but the Midwest experienced a very similar situation a mere five years ago.  Weather patterns in January of 2014 saw temperatures dip to -20˚F and colder in some spots of the Midwest.  The following summer, we still had plenty of insect activity in the region.

Thermometer from a cold and crisp Wisconsin morning. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

Since we don’t see insects bundling up with tiny mittens and scarves, how do they make it through the winter?  It turns out that insects and other arthropods have a number of strategies to help them survive.  For starters, insects typically have a particular life stage (e.g., egg or pupa) that is more tolerant of adverse environmental conditions, such as freezing or desiccation.  Passing through the winter as a more resilient life stage is a good starting point.

Some of the other strategies are surprisingly similar to humans.  Just like snowbirds heading to warmer states for the winter, certain insects like monarch butterflies and green darner dragonflies migrate southward to avoid the coldest temperatures.  Our official state insect (the honey bee) doesn’t migrate, and instead chooses to remain active.  Honey bee colonies shiver together as an insect version of central heating to keep the inside of their hive a constant temperature.  Other insects simply seek shelter and overwinter in protected locations to avoid the worst of the cold.  Insects like the multicolored Asian lady beetle, boxelder bugs, and the invasive brown marmorated stink bug are fond of sneaking into man-made structures to spend the winter.  If insulation and central heating make homes warm enough for us, it’s plenty warm to prevent insects from freezing.  In more natural settings, such insects might end up sheltering in rock piles or beneath the loose bark of a dead tree.  Those locations might not be as toasty as a house, but they can still provide adequate respite from the cold—meaning that insects using this strategy should have been well protected from this year’s cold spell.  Similarly, many insects and other arthropods spend the winter below ground or on the surface of the ground amongst a layer of insulating leaf litter.  In addition, many parts of Wisconsin had a solid covering of snow by the time the polar vortex arrived, so creatures such as ticks had a thick layer of insulation from the coldest of the cold.

Another strategy utilized by insects is the production of natural antifreeze compounds (specific alcohols or proteins) which serve as cryoprotectants to help prevent freezing within their bodies.  We know that a cup of water will turn to ice at 32˚F, but dissolve salts or other substances in that same water and it will require colder temperatures to freeze it.  Insects producing high concentrations of these cryoprotectants can remains unfrozen at surprisingly low temperatures, similar to a bottle of high-proof spirits kept in a freezer.  Taking it even further, the common black and brown woolly bear caterpillars seem to embrace the cold and actually allow ice to gradually form within their bodies.  This may sound like a fatal mistake, but by regulating the formation of ice crystals on their own terms, woolly bear caterpillars are able to control where ice formation occurs and limit it to specific areas of their bodies to prevent damage.  If the same caterpillars were unprepared and froze rapidly, their cells might burst like a can of soda put into a freezer.

The ubiquitous woolly bear caterpillar (Pyrrharctia isabella) is well adapted to winter conditions. Photo credit: Dave Govoni via Flickr.

And then the ash borer
The insect I’ve gotten the most questions about lately has been the emerald ash borer.  While not native to our area, this invasive pest comes from similar latitudes of eastern Asia and the cold-hardy larvae are fortified with cryoprotectants as they spend the winter beneath the bark of ash trees.  These natural antifreeze compounds have their limitations though, and just like sidewalk salt failing to melt ice on a really cold day, the cryoprotectants only work down to certain temperatures before freezing (and death) occurs.  For emerald ash borer, the point at which freezing spontaneously begins to occur (the supercooling point) is when temperatures dip into the range of -13˚F to -23˚F.  This year’s polar vortex did see temperatures fall into and below that range, which would have killed plenty of emerald ash borer larvae, although the insulating effects of the tree bark likely provided some buffering.

The pale end of a surviving emerald ash borer larva sticking out from its tunnel. When larvae are killed by freezing, they typically become discolored. This sample came from the Milwaukee area in early March, 2019. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

Emerald ash borer populations will almost certainly take a hit from this year’s polar vortex, but it’s not going to be a knockout blow.  Give it some time and the reproductive capacity of this invasive species will allow populations to rebound.  The news reports of cold-induced EAB mortality in early February might have been encouraging, but scientific models from the US Forest Service suggest that to really knock down EAB in the long run, we’d have to experience arctic blasts on a regular basis—news that many Midwesterners aren’t likely to receive warmly.


Further Reading: For a great read on how wildlife survive the winter, check out Bernd Heinrich’s Winter World

2018’s Top Trends from the Diagnostic Lab (Part 2)

In this post, we’re continuing to count down the University of Wisconsin Insect Diagnostic Lab’s top arthropod trends of 2018. This is the second half of a two part series; the first half can be found here.


5) White-Lined and Other Sphinx Moths:
The white-lined sphinx moth (Hyles lineata) can be a common species, so encountering one of the 3 inch long hornworm caterpillars isn’t unusual. However, these caterpillars can also be encountered in massive road-traversing hordes if the conditions are just right. From midsummer onwards, large numbers of these caterpillars were observed around the state—in some cases by the tens of thousands. If you didn’t spot any of the caterpillars themselves, you might have encountered the large adult moths with their hummingbird-like behaviour in late summer. Several other sphinx moths species also had a strong presence in 2018, such as the clearwing hummingbird moths and the tobacco and tomato hornworm caterpillars which can regularly be encountered in gardens as they munch away on tomato and pepper plants.

Large, dark-colored hornworm caterpillar of the white-lined sphinx moth on a plant
Large, dark-colored hornworm caterpillar of the white-lined sphinx moth. Photo submitted by Ted Bay, UW-Extension

4) Sawflies:
Sawflies, the caterpillar copycats of the insect world, are a diverse group, so they’re always present to some extent. Last year saw an unexpected abundance of two particular types in Wisconsin—the dogwood sawfly and the non-native Monostegia abdominalis, which feeds on creeping Jenny and related plants from the loosestrife group (Lysimachia species). While sawflies are plant feeders, dogwood sawflies can also damage the soft wood of a home’s siding or trim when these insects excavate small chambers to pupate in. The UW Insect Diagnostic Lab saw a distinct bump in reports of wood damage from the dogwood sawfly last year.

Whitish larva of the dogwood sawfly curled up on a dogwood leaf
Larva of a dogwood sawfly showing the whitish, waxy coating. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

3) Armyworms:
True armyworms (Mythimna unipuncta) can be a dynamic and sporadic pest in the Midwest. This species doesn’t survive the cold winters of our area, so adult armyworm moths must invade from the south each spring. Depending on national weather patterns, the arrival of the adult moths can vary significantly from year to year. If an early mass arrival is followed by abundant food and ideal conditions for the ensuing caterpillars, large populations can result. Once they’ve arrived, true armyworms can go through 2-3 generations in the state and this second generation of caterpillars made an alarming appearance in mid-to-late July. Under the conditions last summer, massive hordes of these caterpillars decimated crop fields before marching across roads by the tens or hundreds of thousands to look for their next meal. In some cases, that next meal included turfgrass, meaning that some Wisconsinites came home from work to biblical hordes of caterpillars and half-eaten lawns in late July.

Striped caterpillar of the true armyworm
Caterpillar of the True Armyworm (Mythimna unipuncta). Photo Credit: Lyssa Seefeldt, University of Wisconsin-Madison Extension

2) Monarch Butterflies:
Much to the delight of fans and conservationists, the iconic monarch butterfly (Danaus plexippus) appeared to have a banner year in the Midwest in 2018. Reports and observations of high numbers of monarchs poured into the Insect Diagnostic Lab during the summer months. As comforting as these reports were, the butterflies still faced a perilous 2,000 mile journey to reach their overwintering grounds in Mexico.  The most consistent measurement of the eastern monarch population comes from estimating the area occupied by the densely-packed overwintering butterflies.  In late January the latest count was released with encouraging news—the eastern monarch population is up 144% over last year and is estimated to be the largest in over a decade.  In contrast, the western monarch population overwinters in southern California and has recently dipped to alarmingly low numbers. Regardless of the winter assessments, monarchs face tough challenges and Wisconsinites are encouraged to help conserve this iconic species.  The Wisconsin Monarch Collaborative recently launched a website with resources for those wishing to join the effort.

Seven monarch butterflies nectaring on a flower
Multiple monarch butterflies nectaring on a single plant in August. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

1) Floodwater Mosquitoes:
Mosquitoes snagged the top spot on 2018’s list for good reason. The upper Great Lakes region is home to over 60 different mosquito species, but one subset—the “floodwater” mosquitoes—drove the storyline last year and impacted outdoor activities through much of the spring and summer months. Mosquitoes in this group, such as the inland floodwater mosquito (Aedes vexans), flourish when heavy rains come. Last year’s mosquito season kicked off in force with a batch of pesky and persistent floodwater mosquitoes just before Memorial Day weekend. Mosquito monitoring traps in southern Wisconsin captured record numbers of mosquitoes shortly thereafter. Later in the year, the Midwest experienced an unprecedented series of severe rainstorms, setting the stage for an encore performance of these mosquitoes. It was this second explosion of mosquitoes that caught the attention of anyone trying to enjoy the outdoors in late summer—a time of the year when mosquitoes are typically winding down in the state.

Ephemeral pools of water created ideal conditions for floodwater mosquitoes in late summer. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

2018’s Top Trends from the Diagnostic Lab (Part 1)

Each year the University of Wisconsin’s Insect Diagnostic Lab receives thousands of arthropod samples and reports from around the state and region, providing a unique perspective into insect and arthropod trends in Wisconsin and beyond.  This post is the first half of a series counting down the top arthropod trends in our area last year.  The second part will be posted in early February and can be found here.


10) Dagger and Tussock Moths:
A few species of fuzzy caterpillars were surprisingly abundant last year and there’s a good chance you might have bumped into these in your own neighborhood.  Two similar-looking yellowish species, the American dagger moth and the white-marked tussock moth, were extremely common around Wisconsin and were two of the most widely reported caterpillars last summer. Another tussock moth associated with milkweed was also surprisingly common in 2018. With many Wisconsinites growing milkweed to attract monarch butterflies, the black and orange caterpillars of the milkweed tussock moth were also noted in abundance around the state last year.

Fuzzy black and orange Caterpillar of the milkweed tussock moth (Euchaetes egle)
Caterpillar of the milkweed tussock moth (Euchaetes egle). Photo Credit: Katja Schulz via Wikipedia

9) Fungus Gnats:
Pick any spot on a Wisconsin map and 2018 was most likely a soggy year. Understandably, rain encourages insects and other creatures that thrive under damp conditions. Last year’s rains created great conditions for fungus gnats, which became quite abundant by late summer. While fungus gnats are harmless to people and pets, they can be an annoyance if present in high numbers. Fungus gnats thrive in damp organic materials, meaning that rich soil, compost piles, and decaying plants can produce masses of these tiny, dark-colored flies. The larvae of these insects can also be common in the soil of houseplants.  As Wisconsinites brought their favorite potted plants indoors in autumn to avoid approaching frosts, reports of indoor fungus gnats were common.

Small dark coloured gnats captured on a yellow sticky card trap
Tiny (2mm long) fungus gnat adults captured on a sticky card trap near indoor plants in fall of 2018. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

8) Purple Carrot Seed Moth:
With several new, non-native insects showing up in Wisconsin every year, the impacts of each species can vary significantly. Some exotics, like the emerald ash borer make massive waves, while others cause merely a ripple. The impacts of one of our newest invasive insects, the purple carrot seed moth (Depressaria depressana), are not yet fully known. This European species was spotted in Wisconsin for the first time last summer and the tiny caterpillars love to feed on the flowers (umbels) of plants from the carrot family. Below-ground plant structures (e.g., the taproots of carrots) aren’t impacted, but notable damage to herbs like dill, fennel, and coriander can occur. As a result, this pest may be a concern for seed producers, commercial herb growers, or home gardeners with a fondness for dill and related herbs. The purple carrot seed moth has been reported in 8 Wisconsin counties thus far [Brown, Columbia, Dodge, Kewaunee, Milwaukee, Racine, Sheboygan and Washington Counties], so new county-level reports are encouraged at the UW Insect Diagnostic Lab.

Tiny (<1/4" long) spotted caterpillar of the purple carrot seed moth on dill.
Caterpillar of the purple carrot seed moth. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

7) Odorous House Ants
Imagine the stereotypical black ants zeroing in on sugary foods at a picnic and you’d have a fitting profile of the odorous house ant (Tapinoma sessile). Of the 100+ ant species in the Midwest, the odorous house ant stood out in spring and early summer last year with its sheer abundance. The UW Insect Diagnostic Lab was flooded with calls about these sugar-loving ants during 2018’s rainy spring, especially when these ants wandered indoors. The spring rains may have forced the ants from waterlogged colonies to seek out higher-and-drier locations, making odorous house ants the most commonly reported ant at the diagnostic lab last spring.

SMall black ant—an odorous house ant worker
Odorous House Ant (Tapinoma sessile) worker. Photo Credit: JJ Harrison via Wikipedia

6) Stink Bugs:
While the Midwest is home to over 50 species of stink bugs, one particular species—the invasive brown marmorated stink bug—stands out to give the rest a particularly bad reputation. If you live in a part of the state with the brown marmorated stink bug, you may have already encountered this species. With its habit of sneaking indoors in the fall, this insect replaced boxelder bugs in some areas as the top home-invading nuisance pest of 2018. This Asian species has made the diagnostic lab’s Top 10 list for several years now and unfortunately doesn’t show any signs of slowing down. In 2018 alone, BMSB was detected in 8 new Wisconsin counties, which hints at potential damage to fruit and other crops in those areas in the coming years.

Adult brown marmorated stink bug
Adult brown marmorated stink bug. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

To see the rest of Wisconsin’s top arthropod trends of 2018, check out part 2, available here in early February.

The Stories that Insects Tell

Imagine taking an American history class where many of the important events were reduced to mere footnotes or skimmed over entirely.  Anyone taking the class would be shocked at this notion—I mean, the Civil War was a big deal after all!  When you look at a different field of study—biology—such a trend has surprisingly occurred, with insects getting the short end of the stick.  Insects are the most diverse and abundant animals on the planet and make up roughly 70% of the 1,000,000+ described animal species.  Yet, many introductory biology textbooks skim over insects (and invertebrates in general) in favor of more charismatic megafauna—a trend that has only gotten worse over time.  Insects may be small, but they serve crucial roles in the world around us from pollinating plants to serving as the base of food webs.  Appropriately, E.O. Wilson referred to insects as “the little things that run the world” in his famous call for their conservation.  It’s difficult to conserve these little creatures that run the world when so few people really get to know them.  

With their sheer diversity and abundance,  knowing the insects also helps us better understand the world, and everyday life, around us.  Getting to know the many different insects is a bit like learning a foreign language.  Travel to an exotic country where you don’t speak the local tongue and you’d have a hard time understanding the everyday happenings around you.  As you picked up words and phrases of that foreign language, things will become easier to understand.  Along these lines, if you can recognize the insects around you, it helps interpret the stories they tell.  Truly knowing your insects is like possessing an all-powerful decoder ring to the untold stories that surround us.  

Let’s look to flies to illustrate this point.  To many folks, a small fly found in their home is assumed to be a fruit fly, and a large fly, a house fly.  But there are dozens of different flies that commonly show up indoors—each with their own story to tell.  Fungus gnats hint at overwatered houseplants, moth flies indicate build-up in a bathtub drain, and metallic blow flies can alert you to a mouse trap in need of checking.  Outdoors, other species of flies can provide clues that gauge water quality, indicate the presence of specific plants, or solve crimesbut only if one knows how to interpret their clues.  If a picture is worth a thousand words, I’d argue that a properly identified insect is worth even more.  

The unusual fly species, Asteia baeta. At only 2mm long, these flies can readily be mistaken for fruit flies to the naked eye. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

This holiday season, my own love of insects led to a scientific discovery that would have gone unrecognized in most households.  A day after setting up our “real” Christmas tree, I noticed several tiny flies at the windows of our home.  My curiosity was piqued and like any good detective, some sleuthing was needed.  I recall an undergraduate professor telling the class, “a biologist without a notebook is off duty” to which I’d add, “an entomologist without vials is off duty”.  So now I was off, vials in hand, on an insect hunt in my own house.  Once the specimens were examined under the microscope, I recognized the flies as a rare species (Asteia baeta) from the poorly-known family Asteiidae.  There isn’t much written about these flies, but they’re known to be associated with fungi, vegetation, and tree sap, which told me that the new Christmas tree was the source.  These flies have only been spotted in Wisconsin a few times and no preserved specimens exist for that family in the Wisconsin Insect Research Collection (I’ll be donating some soon).  Looks like our Christmas tree came with it’s own entomological story to tell this year—I’m glad I knew how to listen.

The source of the unusual flies—apparently our cat wanted to try and hunt for them as well. Photo Credit: PJ Liesch

2018 Update: Brown Marmorated Stink Bug in Wisconsin

Author’s Note: Original post updated in January, 2019 due to a confirmed report in Waupaca Co. and suspected report in Oneida Co.


One of the most concerning invasive insects to appear in Wisconsin in the last decade is the brown marmorated stink bug (Halyomorpha halys).  This Asian species delivers a double-whammy of not only damaging crops and other plants, but also being a significant nuisance when it sneaks into buildings in the fall. Since its initial detection in the state in 2010, populations of this insect have built up slowly but steadily. 

Brown marmorated stink bug adult on the side of a building in fall. This is becoming a common site in some parts of the Midwest. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab.

What’s the current status of BMSB in Wisconsin?

As of late 2018, 28 counties have confirmed reports of the brown marmorated stink bug and a handful of other countries have suspected sightings.  This insect has a strong foothold in the state and was confirmed in eight new counties in 2018 alone—Eau Claire, Jackson, La Crosse, Marquette, Monroe, Richland, Trempealeau, and Waupaca counties. 

Distribution of the brown marmorated stink bug in Wisconsin—updated January 4th, 2019
Distribution of the brown marmorated stink bug in Wisconsin—updated January 4th, 2019. BMSB has been confirmed in 28 counties. Map Credit: PJ Liesch, UW Insect Diagnostic Lab.

Two core areas currently stand out for brown marmorated stink bug activity in Wisconsin: the Highway 41 corridor from Fond du Lac up to Green Bay and southern Wisconsin from Dane and Rock Counties east to the Milwaukee metro area.  These two areas have the longest history of BMSB in the state and account for the majority of reports thus far. 

Much of the state has yet to encounter this insect or truly experience its impacts.  When the brown marmorated stink bug is first detected in an area, there’s a proverbial “calm before the storm”.   The pattern observed in the state thus far has been a few “quiet” years where low initial populations of this insect result in only a few sightings annually.  However, after a few years in a given area, BMSB populations build up to the point where nuisance problems around structures are noted and reports of potential plant damage begin to trickle in.

What’s the Outlook for BMSB?

Unfortunately, Wisconsin has yet to see the full impact of this invasive insect.  Observations over the last few years have found that BMSB is able to survive our winters and reproduce in the state, so this adaptable pest will most likely continue to build its numbers in the coming years. 

Over time, the brown marmorated stink bug is likely to emerge as one of the top structure-invading pests in the state alongside the likes of boxelder bugs and multicolored Asian lady beetles.  In the eastern US, where BMSB has been established for over a decade in spots, problems can be significant.  In some cases these malodorous insects have been documented invading homes by the tens of thousands

Several brown marmorated stink bug juveniles on a dogwood shrub. Ornamental trees/shrubs, vegetables, and fruit crops can all be attacked by this insect. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab.

While widespread crop damage has not yet been observed in Wisconsin, it may only be a matter of time as population of this insect continue to build in the state.  Agricultural problems have also been significant in the eastern US, giving us a glimpse into what could potentially happen in coming years.  For example, brown marmorated stink bug caused $37 million dollars in losses to apples in the mid-Atlantic states in 2010 alone.  

Having been detected in Portage County in 2017, brown marmorated stink bug may soon start to pose a threat to vegetable production in central Wisconsin.  Similarly, specimens confirmed from Door County in 2017 are forcing fruit growers in that part of the state to keep a close watch on their orchards and vineyards.  With the recent detection of BMSB in several western Wisconsin counties, we’ll likely see BMSB populations slowly build in that part of the state over the next few years as well. 

What should you do?

A Wood-Boring Insect Mystery

Imagine it’s August and as you wander in from your backyard, you notice a small pile of sawdust at the bottom of the door frame.  It might not be much sawdust, but you also find a few holes in the wood trim nearby.  It definitely seems to be insect damage, but who’s the culprit?

Unexpected insect damage to wood trim.

If you came up with a list of insects in the upper Midwest that can damage the wood of your home, it wouldn’t be terribly long.  For good reason, termites might be the first insect to come to mind, although our eastern subterranean termites are restricted to isolated pockets and are not commonly encountered in Wisconsin.  A close second on the list might be carpenter ants.  Interestingly, carpenter ants don’t technically eat (e.g., digest) wood and merely excavate soft, rotting wood to create a nesting site.  If anything, their presence in a home might be an indicator of a water damage.  Powderpost beetles can also attack wood and are commonly encountered in old barn beams and log cabins.  Carpenter bees help round out a list of the “usual suspects”.  These wood-boring bees can create good sized holes (a half inch across), although with their preference for unpainted softwoods used for trim, siding, and fence posts, their damage is mostly cosmetic in nature. 

Then another clue comes to mind—the nearby shrubs that had been eaten by some kind of worm-like insect over the past few weeks. 

Larva of a dogwood sawfly showing the whitish, waxy coating. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

When it comes to wood-damaging pests, sawflies generally don’t come to mind.  Sawfly larvae—Mother Nature’s caterpillar copycats—tend to feed on plant leaves.  Species like the European pine sawfly, dusky birch sawfly, rose slug sawfly, Columbine sawfly, pearslug sawfly, and birch leafminer sawfly can all be commonly encountered feeding on plants during the growing season.  One species that was common in 2018—the dogwood sawfly—is unique in that it not only causes plant damage but can also damage wood trim and siding of homes.  The dogwood sawfly is one of our commonest pests of native and landscape dogwoods (Cornus spp.).  When larvae are small,  they have a whitish waxy coating thought to mimic bird droppings and they can often be found curled up on the undersides of dogwood leaves.  As larvae mature, they lose the waxy coating and their black and yellow coloration becomes conspicuous.   

Mature dogwood sawfly larva with classic black and yellow appearance.

So how does this plant-feeding species end up damaging wood?  As is the case with any insect that undergoes complete metamorphosis, the larvae need to pass through the pupal stage to make it to adulthood. Insect pupae, however, are generally immobile can make an an easy meal for any predator that stumbles upon them.  Thus, many insects seek out tucked away spots to complete their pupal stage.  When ready to pupate, dogwood sawfly larvae typically create their own hideaway by chewing small chambers in rotting wood such as twigs, branches, or logs near the shrub they had been feeding on. 

Small chambers chewed into a fallen twig—a “typical” spot for dogwood sawfly to pupate.

If rotting wood is unavailable, the larvae may turn to other nearby wood materials—including wood trim and siding.  This typically occurs when larvae had been feeding on ornamental dogwood shrubs planted close to a home.  In the grand scheme of things, these insects don’t cause that much damage to wood, although homeowners won’t be thrilled if they’ve been caught off guard by this unexpected wood-damaging pest! 

Department of Entomology

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