All posts by pliesch

A Wandering Horde of…Millipedes

It’s a dark, overcast night as the horde emerges from the nearby woods. There’s no real coordination, but thousands of them—perhaps tens or even hundreds of thousands—seem to wander aimlessly through the yard.  Some approach the darkened farmhouse and a few even manage to make it inside…

If this were and episode of The Walking Dead, the protagonists would be in a tough spot, but we’re not talking about zombies in this case.  Instead, the topic is millipedes, which have been surprisingly abundant this summer in parts of the Upper Midwest.

Greenhouse millipede.
Greenhouse Millipede (Oxidus gracilis). Photo Credit: Joseph Berger, Bugwood.org

Most everyone is familiar with millipedes.  They technically aren’t insects, but they are related as demonstrated by their segmented legs and “crunchy” exoskeleton (both are types of arthropods).  These multi-segmented, worm-like creatures can be common in damp areas and are perhaps most recognizable by their slow walk and their habit of curling into a spiral when disturbed.

Unlike the zombies portrayed in on TV, millipedes are really quite harmless.  Some millipede species have been documented as minor crop pests, but in the grand scheme of things, I mostly think of millipedes as being beneficial detritivores.  Millipedes feed on decaying plant materials and they return nutrients to the soil.  Their feeding also breaks down plant materials into smaller pieces, allowing microbes to more easily assist in the decomposition process.  Millipedes can be especially common in damp locations with abundant plant materials: compost piles, rich soil with high organic content, mulch beds, wooded or prairie areas, CRP land, lawns with a heavy thatch layer, and similar.

Millipede curled up in a spiral
A millipede curled up in a classic defensive posture to protect its legs. Photo credit: Joseph O’Brien, USDA Forest Service, Bugwood.org

While mostly beneficial, millipedes can occur in very high numbers under the right conditions and can be a nuisance when they seem to suddenly appear in yards and homes.  Hopkin and Read’s The Biology of Millipedes (1992) describes situations where massive millipede hordes have covered acre after acre of farmland or stopped trains, quite literally, in their tracks.  The Midwest does see large masses of millipedes on occasion and it was a particularly busy year at the UW Insect Diagnostic Lab for calls about these creatures.

The reasons behind millipede mass migrations aren’t fully understood, but moisture is often noted as a common factor.  Other potential reasons range from general weather patterns to habitat disruption, competition, and reproduction.  When millipedes do move about, many species shun the sun and prefer to move at night or during very overcast days.  When they encounter a building, millipedes can sneak inside, although this is really accidental—it’s too dry for them to survive indoors and they typically die within a day or two.

Millipedes on a home's foundation
Thousands of millipedes along a resident’s home. From a case submitted to the UW Insect Diagnostic Lab this summer.

Millipedes can be frustrating when mass migrations occur as there’s not much that can be done to completely stop them.  It’s not uncommon to have cases where hundreds or thousands of of millipedes crawl onto the foundation or siding of a home every night.  If they mostly stay outside, that’s one thing, but this summer I’ve had multiple cases where large numbers of millipedes (hundreds) had snuck under a building’s siding and then rained down through ceiling light fixtures.  This sounds like something out of a sci-fi film, but if you were trying to sell your home it could be a real-life nightmare scenario.  In such cases, there simply isn’t any way to make the millipedes magically disappear.  Insecticides may be tempting but only help to a certain extent because more millipedes can simply show up the next day.

If you’re staring down a millipede horde, one of the most important approaches is physical exclusion.  Inspecting the exterior of a home and physically sealing up cracks, crevices, and other potential entrance points with caulk, expanding foam, or new weather stripping can be a chemical free, long-term solution to at least keep millipedes outdoors.  Because millipedes prefer damp areas with decaying plant material, keeping landscape pants, fallen leaves, and thick layers of mulch away from the foundation of a home could also help reduce hiding areas for millipedes.

Luckily, millipede mass migrations eventually run their course and quiet down on their own.   This year, I saw a spike in millipede reports starting in mid-June and running into early August before subsiding.

Masked Hunter Bugs: Another Kissing Bug Look-Alike

“I think I’ve found a kissing bug and wanted to report it” is a surprisingly common line I get at the UW Insect Diagnostic Lab.

I’ve previously written about kissing bugs, but to quickly recap: these are blood-feeding assassin bugs found primarily in South and Central America.  Kissing bugs tend to be associated with vertebrate nests outdoors but can bite humans and can also carry Trypanosoma cruzia parasite that causes Chagas disease.  Due to this concern, I see a spike in website traffic and “reports” of suspected kissing bugs just about any time there’s national news coverage of these insects. While many kissing bug species exist, the vast majority are restricted to tropical and subtropical areas.  The northernmost species—the eastern conenose kissing bug (Triatoma sanguisuga)—ranges from Latin America as far north as southern Illinois.

Eastern conenose kissing bug adult.
Eastern conenose kissing bug adult. Photo credit: Robert Webster, via Wikipedia

Insects don’t care for geopolitical boundaries, but when humans shade in the entire state of Illinois on a distribution map of kissing bugs, it gives the false impression that these insects are on the tollway marching towards Wisconsin’s southern border.  However, the eastern conenose kissing bug is rarely spotted in the northern parts of its range and there has never been a verified case of kissing bugs from within Wisconsin.

The regular occurrence of false reports can likely be attributed to hype in the news combined with a good ol’ case of mistaken identity.  It turns out that there are a number of common insects that can resemble kissing bugs.  One of these, the western conifer seed bug (Leptoglossus occidentalis), is regularly encountered in the upper Midwest because these insects sneak indoors in the fall just like boxelder bugs.  Recently, the commonest look-alike I’ve been getting reports of is the masked hunter bug (Reduvius personatus), which can also be encountered indoors.

If you aren’t familiar with masked hunter bugs, there’s a good reason why these insects can sometimes mistaken for kissing bugs—they’re technically kissing cousins.  Both kissing bugs and masked hunter bugs belong to the assassin bug family (Family Reduviidae).  This is a diverse family of approximately 7,000 species worldwide and we have dozens of common species in the Midwest.  The vast majority of these species (including masked hunter bugs) are really beneficial predators of other arthropods and are of little medical importance.  In theory, if you picked up and mishandled one of our Midwestern assassin bugs species, it could bite—likely feeling similar to a wasp sting—although that’s about the worst it could do.

Juvenile masked hunter bug camouflaged with debris.
Juvenile masked hunter bug camouflaged with debris. Photo Credit: Chiswick Chap, via Wikipedia

Masked hunter bugs are readily identifiable, although the nymphs (juveniles) can have you scratching your head if you haven’t encountered them before.  The nymphs are often ¼” – ½” long and camouflage themselves with bits of lint and other debris—as a result, they can resemble miniature walking dust bunnies.  Once you recognize this disguise, they’re easy to identify.

Masked Hunter Bug Adult.
Masked Hunter Bug Adult. Photo credit: JP Hamon, via wikipedia

Adult masked hunter bugs are slender, roughly ¾” long, and entirely dark coloured.  They have long, thin legs & antennae and stout beak-like mouthparts which they use to feed on insects and other arthropod prey.  Several key features help distinguish masked hunter bugs from eastern conenose kissing bugs:

  1. Masked hunter bugs are entirely dark while eastern conenose kissing bugs have red on their body
  2. Masked hunter bugs lack the projecting “conenose” present on the head of kissing bugs
  3. Masked hunter bugs have a bulging, “muscular” appearance of their prothorax (trapezoidal region behind the head) when viewed under magnification
  4. Masked hunter bugs have stout beak-like mouthparts while kissing bugs have long, slender mouthparts when viewed under magnification

Side-by-side comparison of a kissing bug and a masked hunter bug.
Side-by-side comparison of a kissing bug and a masked hunter bug. Photo Credit: Devon Pierret and PJ Liesch, UW Insect Diagnostic Lab. [Click for full sized version]
When it comes to kissing bugs, we simply don’t have these insects in the Upper Midwest, but we do have look-alikes.  For side-by-side diagrams showing an eastern conenose kissing bug compared to common look-alikes, visit the ID Guide page on this website: labs.russell.wisc.edu/insectlab/visual-id-guides/

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.

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