Sphinx Moths—Hovering at a Flower Near You

If you’ve watched the flowers in your yard or local park recently, you might have noticed some surprising visitors hovering at the flowers—the hummingbird-like sphinx moths.  Several species in the “sphinx” or “hawk” moth group (Family Sphingidae) are known for their day-flying, hummingbird-like behavior.  From a distance these moths can easily be mistaken for hummingbirds as they skillfully maneuver from flower-to-flower sipping nectar with their long mouthparts.

One of the commonest members of this group in Wisconsin is the white lined sphinx moth (Hyles lineata).  With a wingspan of nearly 4 inches, it’s easy to understand why this species can be mistaken for a hummingbird as it feeds.  The greyish adults are easy to pick out and a white stripe on each forewing helps identify them in the field.  The caterpillars (hornworms) of this species reach nearly 3 inches in length and can feed on a wide range of plants.  While this species is regularly encountered in the Midwest, this year has been especially good for white-lined sphinx moths in Wisconsin.  In mid-to-late July I received many reports of the caterpillars—sometimes in astounding numbers.  In several instances, “outbreaks” of tens of thousands of these large caterpillars were spotted as they migrated across roadways from agricultural fields.  The multitudes of caterpillars have since pupated and transformed into nectar-loving moths—leading to a recent spike of sightings.

White-lined sphinx moth (Hyles lineata). Photo Credit: Andy Reago & Chrissy McClarren; Wikipedia

In addition to the white-lined sphinx moth, several other hummingbird-like sphinx moths have been common this year—the “clearwing” hummingbird moths (Hemaris spp.) and the Nessus sphinx moth (Amphion floridensis).

The rusty-colored “clearwing” moths (Hemaris spp.) are smaller than the white-lined sphinx moth, and have a wingspan of approximately 2 inches.  Their shaggy appearance and patches of yellow coloration lend a resemblance to large bumble bees.  Characteristic transparent “windows” in the wings help identify these moths.  Several Hemaris species can be encountered in the Great Lakes region with subtle differences in appearance and biology.  Both the “hummingbird clearwing” (Hemaris thysbe) and the “snowberry clearwing” (Hemaris diffinis) can be common, while the “slender clearwing” (Hemaris gracilis) is associated with pine barrens and is rarely encountered.

The hummingbird clearwing moth (Hemaris thysbe) showing the transparent “windows” in the wings. Photo Credit: Andy Reago & Chrissy McClarren; Wikipedia

The “Nessus Sphinx” (Amphion floridensis) is another hummingbird mimic that was commonly reported earlier in the summer.  Although somewhat similar in size and coloration to the Hemaris clearwing species, the Nessus sphinx moth has opaque wings and two distinct yellow bands across the abdomen.

The Nessus sphinx moth (Amphion floridensis) in action. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

In addition to being a joy to observe, sphinx moths are a great example of “non-bee” pollinators.  Their unique behavior and anatomy allows them to form interesting relationships with some of the plants they pollinate.  In an extreme example, the Christmas Star Orchid (Angraecum sesquipedale) from Madagascar possess extremely long tube-like floral structures which contain the nectar.  Upon learning of the unique anatomy of this orchid, the famed naturalist Charles Darwin speculated that a moth with equally long mouthparts must exist to pollinate them.  It took over a century to document, but a sphinx moth wielding foot-long mouthparts was finally observed pollinating the Christmas Star Orchid.

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.

Chinch Bug: How a Tiny Insect Helped the Rise of Dairy in Wisconsin

It was over 170 years ago that Wisconsin was granted statehood.  While much has changed over the decades, some things haven’t—like the omnipresence of agriculture.  It’s hard not to notice agriculture in Wisconsin, be it crop fields, orchards and vineyards, or our famous dairy farms dotting the landscape.  To many, Wisconsin is practically synonymous with dairy, and America’s Dairyland is even enshrined on our license plates.  While Wisconsinites may take our dairy prominence for granted, it turns out we weren’t always the Dairy State—at one point in history, you might have even called us the Wheat State.

It’s easy to understand why Wisconsin has a long history of agriculture.  The region received an influx of rich soil with the last ice age which allowed us to become a top wheat producer in the early days of statehood.  To early farmers in Wisconsin, wheat was a profitable crop in high demand.  For a period in the 1800’s, Milwaukee was even the busiest wheat shipping port in the entire world1.  Fast forward to today and Wisconsin is best known for its dairy production, while states like Kansas, Nebraska, and the Dakotas are known for their bountiful grains.

Quote from J.G. Thompson’s The Rise and Decline of the Wheat Growing Industry in Wisconsin2

It was the mid-to-late 1800’s when the course of Wisconsin’s history was forever altered by a number of factors.  Fluctuating wheat prices and overworked soil might have been the primary drivers, but dry weather and a tiny insect also pulled on the reins of history.  Just as mosquitoes can thrive after heavy rains, other insects thrive under hot, dry conditions.  Droughts of the 1860s, 70s, and 80s set the stage for biblical outbreaks of some of these insects.  Farther to the west, fields in the Great Plains fell victim to swarms of Rocky Mountain locusts so massive that they darkened the sky for thousands of square miles.

Closer to home, the pest delivering a coup de grâce to wheat fields was the humble chinch bug, which thrived under the dry conditions at the time.  Chinch bugs aren’t much to write home about: at roughly an eighth of an inch long, most folks wouldn’t take the time to examine these tiny, black and white insects.  It was by their sheer abundance that these creatures decimated Wisconsin’s wheat fields in the 1800’s.  Using needle-like mouthparts, these insects sucked the life out of wheat plants, leaving behind wilted, yellowed stems.

The chinch bug (Blissus leucopterus). Photo Credit: David Shetlar, The Ohio State University, Bugwood.org.

When a pest outbreak occurs in a given year, a farmer might chalk it up to bad luck, bad weather, or other factors and hope things improve the next season.  With falling wheat prices and chinch bugs regularly devastating wheat crops in the late 1800’s, Wisconsin wheat farmers realized that their efforts yielded little profit.  Without an effective way to prevent the ravages of the chinch bugs, attentions shifted to more fruitful possibilities.

The first comprehensive report on the biology and habits of the chinch bug.

Understanding the biology of the chinch bug was crucial to discovering the limitations of that insect’s destruction.  It turns out that chinch bugs are picky eaters with a taste for grasses—wheat, corn, and similar.  Unrelated plants, including forage crops like alfalfa, weren’t affected by these insects and could be grown to feed livestock at the very time that the dairy industry was budding in Wisconsin.  Decades later our dairy prominence is featured on our license plates.  

When enjoying those Wisconsin cheese curds, ice cream, and other dairy treats during national dairy month, chances are you probably wouldn’t have thought about insects—but now you know how the tiny chinch bug helped make dairy a BIG deal in Wisconsin.


1Harbor and Marine Interests. History of Milwaukee City and County Vol I. Ed. W.G. Bruce. 1922. Print.

2J.G. Thompson. The Rise and Decline of the Wheat Growing Industry in Wisconsin. Bulletin of the University of Wisconsin No. 292. Economic and Political Science Series. Volume V(3): 295-544. 1909. Print.

Black Widows: The Hermits of Door County

Spider cases at the UW Insect Diagnostic Lab often boil down to clients wondering if they’ve found either a brown recluse or black widow spider.  Wisconsin is home to approximately 500 species of spiders, and essentially all of these are harmless, beneficial creatures that provide us with an astonishing amount of free pest control*.  While we’re outside the native range of the dreaded, but horribly misunderstood brown recluse spider (Loxosceles reclusa), Wisconsin is actually home to a native black widow species—the northern black widow (Latrodectus variolus).  In Wisconsin, these spiders are rare and have been documented in fewer than 10 counties.  Most Wisconsinites will go their entire lives without seeing a northern black widow out in nature and if you’re lucky enough to spot one of these elusive creatures, you’d almost certainly encounter a lone individual.  In contrast, there are several other widow spiders that can be much more common in other parts of the country.

The vast majority of black widow records in Wisconsin are from the east-central counties.  Door county historically stands out as having the most confirmed sightings and perhaps takes the place of Wisconsin’s black widow “capital”—although only a few sightings occur in most years.  The northern black widow doesn’t seem to occur farther north under natural conditions, which suggests an inability to the survive colder winters in the northern part of the state.  Along these lines, Door county’s unique geography and the moderating effects of Lake Michigan may explain why the majority of reports come from that part of Wisconsin.  Similarly, other confirmed reports of the northern black widow tend to be from nearby counties bordering Lake Michigan.  Away from the lake, northern black widows have also been documented in prairie areas in Crawford, Grant, and Sauk counties, where the microclimate on south-facing slopes may favor their survival.

“Scarlet”—the first Northern Black Widow documented in Sheboygan County. Photo Credit: PJ Liesch-UW Entomology

In a typical year, the UW Insect Diagnostic Lab might get a report or two of black widow spiders, but 2017 stood out in the sheer number of reports.  For spiders like the black widow, I keep in touch with Dr. Mike Draney, an arachnologist at UW-Green Bay.  During some stretches of 2017, Mike and I were emailing reports of black widows to each other once or twice a week!  These reports generally came from Door county and nearby areas.  In addition, these spiders were also documented in two additional Wisconsin counties for the first time last year: Brown county and Sheboygan county.

It’s possible that winter weather patterns might explain the distinct bump in northern black widow sightings last year.  Leading up to 2017, Wisconsin faced two consecutive mild winters, which might have favored insects, spiders, and other creatures that fare better in slightly warmer climates.  While the state did see an increase in reports last year, it’s not yet known if that trend will continue in 2018 as the state just emerged from a veritable winter season.


*A recent study estimated that spiders around the globe consume approximately 400 – 800 million tons of prey annually. Nyffeler, M. & Birkhofer, K. Sci Nat (2017) 104: 30. https://doi.org/10.1007/s00114-017-1440-1

To Boldly Go Where Man Has Gone Before: Pests on the Move

Since the earliest days of mankind, we’ve excelled at exploring and expanding our presence to nearly every spot on the map With all our wanderlust, we’ve been equally adept at taking other species with us as we go—often with unintended consequences. 

In some situations, species have been deliberately moved by humans: livestock to the new world, the introduction of birds from Shakespeare’s plays into Central Park,  and even the notorious gypsy moth was transported from Europe in a failed attempt at an American silkmoth industry On top of that, there’s an extraordinarily long list of species that have been accidentally moved, with significant impacts Stowaway rats on the ships of European explorers and traders would be one of the most notorious examples Rats introduced to new island environments wreak havoc on native birds and reptiles by devouring vulnerable eggs Insects have also been transported around the globe with devastating results and some of North America’s most important and emerging insect pests originate elsewhere on the planet: Japanese beetle, emerald ash borer, brown marmorated stink bug, and the spotted lanternfly.

Aedes sp. mosquitoes preparing for a blood meal.  Photo Credit: Ary Farajollahi, Bugwood.org.

One of the insects best adapted to follow humans is the notorious mosquito Certain mosquito species (peridomestic species) possess traits that allow them to take advantage of conditions in areas disturbed by humans and thrive in those spots.  With humans came environmental modification, construction, and discarded trash of one kind or another.  Some mosquitoes might have originally relied on the water pooled in natural containers, such as rotted out tree stumps to reproduce, but can just as easily take advantage of water-filled containers, ditches, and other artificial habitats.

In modern times, automotive tires have become a key habitat for certain mosquito species Tires not only are perfect objects for holding water for extended periods, but they also provide the dark, sheltered habitat favored by some female mosquitoes looking to lay eggs Tires are an important way for mosquitoes, like the Asian Tiger Mosquito (Aedes albopictus) to be moved into and around the US (including the Midwest) Other species, like the Asian Rock Pool Mosquito (Ochlerotatus japonicus), are also easily transported in human materials.

Hyacinth flower sold from a local store, including a vase pre-filled with water. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

A recent case at the UW Insect Diagnostic Lab illustrates the ease with which non-native mosquitoes can be moved around the country In the first part of 2018, stores have been selling hyacinth bulbs in vases pre-filled with water as a way to force the bulbs to bloom into a flash of color during the dreary winter months In a recent discovery in southeastern Wisconsin, a vase purchased at a local store ended up yielding half a dozen larvae of the non-native Asian rock pool mosquito.  The exact origin of the mosquitoes isn’t known at this time.

A bonus surprise with the flowers—larvae of the Asian rock pool mosquito (Ochlerotatus japonicus). Animation credit: PJ Liesch, UW Insect Diagnostic Lab.

These mosquitoes won’t be much of a concern in the grand scheme of things as Ochlerotatus japonicus has been present in Wisconsin for over a decade and is already established hereHowever, such cases do leave open the possibility of non-native mosquitoes being moved into parts of the country where these pests have not been encountered beforeWhere humans go, pests will boldly follow.

Bobbleheads of the Insect World

During the winter months, I often get reports of intimidating-looking, but harmless and quirky wasp-like creatures known as “wood wasps” (Family Xiphydriidae).  What makes them quirky?—They’re basically the bobbleheads of the insect world, which always reminds me of going to baseball games as a kid.

Having “wasp” in the name can evoke a certain amount of anxiety, and you can already guess that wood wasps are related to the yellowjackets and paperwasps of late summer.  However, the wood wasps belong to an early branch within ant/bee/wasp group (the Order Hymenoptera) and lack the anatomical structures and ability to sting.

Side view of a “wood wasp” showing the scrawny “neck” and “bobblehead” appearance. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

Wood wasps have a distinct appearance, so once you’ve trained your eye, they’ll be hard to miss the next time around.  These insects tend to be about an inch long with slender, dark-colored bodies and orange legs.  There are often some pale stripes or patches on or just behind the head and in some cases the tips of the antennae can be pale as well.  The most diagnostic feature gives wood wasps their bobblehead status in my book—the bulbous head of these insects is attached by a scrawny “neck” when viewed from the side.  You can even imagine it bobbing back and forth, if only a tiny spring were attached.

You might ask yourself, how are these insect bobbleheads active in winter when most other insects are scarce?  The answer boils down to firewood.  The pale, grub-like larvae of wood wasps live in the wood of dead or dying trees.  When these trees are chopped into firewood, we end up hand-carrying the insects into our cozy winter abode.  If the wood isn’t used in the fireplace right away, the larvae take advantage of the spring-like conditions and transform into active adults indoors.  To those unfamiliar with wood wasps, you can scratch your head for days trying to find the source, but once you recognize them and their origins, moving the firewood to a colder location is the simple fix.

Under the Microscope: Arthropod Trends of 2017

Over 2,500 cases flowed through the doors of the UW Insect Diagnostic Lab last year, ranging from the typical June beetles through bizarre creatures that most humans will never see in their entire lives (like the itch-inducing pyemotes grain mite).  Perhaps Forrest Gump said it best when he quipped, “life was like a box of chocolates—you never know what you’re gonna get.”  A distinction amongst insects, however, is that the “box” contains 20,000+ possibilities in Wisconsin alone and over well 1,000,000 globally.  With that said, a year at the UW Insect Diagnostic Lab is like having one humongous, box of really awesome chocolates, without all the calories.

Finding a pyemotes itch mite is like trying to find a needle in a haystack, except in this case these microscopic mites were in a farmer’s batch of corn. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

With insects and related creatures, the weather can of course have a big impact and there definitely were examples of this in 2017.  The current cold winter aside, the last two winters had been otherwise mild, giving a few insects suited for warmer conditions a chance to inch their way northward.  Last spring and summer, this meant a bunch of sightings of an otherwise uncommon bee for our area known as the carpenter bee due to its habit of tunneling into unpainted cedar trim and other wood.  In a typical year, I might see a few cases out of the southeastern corner of Wisconsin, but 2017 had regular reports of these bumble bee look-alikes during the spring and summer months.  Similarly, praying mantids often meet their maker at the hands of a cold winter, but were surprisingly abundant in late summer and fall of last year.  Ticks were also extremely abundant last spring and with the rainy start to the summer, mosquito numbers were at an all-time high in some traps.  Mosquitoes were also a big deal in the news, with Wisconsin’s first confirmed reports of the Asian Tiger Mosquito last July.

Asian Tiger Mosquito (Aedes albopictus). Photo credit: James Gathany, Centers for Disease Control

The creature that amassed the most phone calls and emails in 2017 was the notorious Japanese beetle, which likely also benefited from the warmer than average winters these past few years.  For Wisconsin gardeners and farmers, the Japanese beetle is certainly a formidable foe, but at least there are ways to mitigate the damage.  In contrast, there’s another destructive pest wiggling its way into the spotlight in the state, which is much more difficult to control—an invasive earthworm commonly known as the jumping worm.  While they may not be insects, these earthworms are creepy-crawly and can wreak havoc in  gardens and flower beds, so I received a fair number of reports and questions.  What stood out to me in last year was the rapidity with which these destructive worms have been moved around the state (moved—as in humans have moved soil, plants, mulch, and similar materials).  Jumping worms were first found in the state in 2013 (in Madison), but have now been spotted in roughly half of the counties in Wisconsin.  To make matters worse, we don’t have any highly effective tactics to prevent these worms from turning rich garden soil into the consistency of dry, crusted coffee grounds—gardeners beware!

Speaking of invasive species, the emerald ash borer has continued its march through the state and now has footholds in some of our northern counties including Chippewa, Douglas, Eau Claire, Marathon, Marinette, Oneida, and Sawyer counties.  Unfortunately, our greatest concentrations of ash trees are in the northern part of the state (e.g. black ash in swampy areas), and the loss of ash from northern wetland areas could result in significant ecosystem effects.  Other recent invaders like the spotted wing drosophila and the brown marmorated stink bug had busy years as well.

Rusty patched bumble bee (Bombus affinis) visiting a flower in Middleton, WI. Photo credit: Rick Terrien

In other insect news, it seemed to be a good year for monarch butterflies in 2017, and the rusty-patched bumble bee finally made it onto the federal endangered species list. I was pleasantly surprised by a number of confirmed sightings of the rusty-patched bumble bee in the state as well. Perhaps my favorite “bug” story for the year involved black widow spiders.  It’s not common knowledge, but we do technically have a native black widow species in the state (Northern Black Widow, Latrodectus variolus).  It’s a reclusive species and is rarely encountered in Wisconsin, but reports trickled in once or twice a week at some points during the summer months (details to follow in a future blog post).

With so many cases last year, we’re really only touching the tips of the antennae.  If you’re interested in hearing more of the unusual stories from the UW Insect Diagnostic Lab, I’ll be giving a “highlight” talk on May 4th on the UW campus.

 

 

 

Mantid Mania

If you spotted one of the unusually large green or brownish insects working on its kung fu moves in late summer, you would have undoubtedly spotted a praying mantis.  These insects are an unusual sight in Wisconsin as we really don’t have native mantids in our area.  The closest native mantid, the Carolina mantis (Stagmomantis carolina), occurs in the southeastern US and does makes its way as far north as Iowa, Illinois, and Indiana.  A stray may show up in Wisconsin on occasion, but this seems to be an exception, rather than the norm.

A female Chinese Mantis (Tenodera sinensis) blends in on vegetation in late summer. Photo credit: Jill Schneider.

When mantids are found in the upper Midwest, the culprits are typically two introduced species: the European mantis (Mantis religiosa) and the Chinese mantis (Tenodera sinensis).  Both of these species have been in the country since the late 1800’s and have become well established in North America.  Of these, the Chinese mantis stands out with its sheer size as it can approach 5 inches in length with its outstretched legs.  The Chinese mantis is our largest and commonest species, based on observations.

Overall, mantids are much more common in southern states. The scarcity of these insects in the upper Midwest has a lot to do with their life cycle.  For the species in our region, females lay egg pouches (oothecae) in late summer or early fall in exposed locations—twigs, gardening stakes, and similar spots.  If there’s a harsh winter, these exposed egg masses face the brunt of the cold and mortality is high.  As a result, the vast majority of Wisconsin’s mantid sightings are restricted to southern and eastern counties where temperatures are slightly warmer during the winter months.  In 2017, there was a distinct increase in mantid sightings, likely due to the two consecutive mild winters in our area.  Assuming an egg case makes it through the winter, hundreds of juvenile mantids emerge in spring and surviving individuals reach maturity by late summer.

Chinese mantis (Tenodera sinensis) cleaning a leg. Note the enlarged (“Popeye-like”) raptorial forelegs lined with spines to subdue prey. Photo Credit: Jill Schneider.

Not only are mantids fascinating creatures to watch, but they’re impressive predators as well.  A number of adaptations place mantids amongst the top predators of the insect world.  First off, large eyes give them excellent stereoptic vision—if you’ve ever watched a mantis, they’ve watched you as well.  Camouflage also benefits many mantids, with color patterns that allow them to stealthily hide on plants, waiting to ambush unsuspecting prey with ninja-like agility.  The tropical orchid mantis (Hymenopus coronatus), even takes camouflage to an extreme with bright pink coloration to blend in on flowers.   The grisliest adaptation would be the enlarged “raptorial” forelegs armed with spines, which allow mantids to rapidly seize and impale prey and hold them in a final, lethal embrace as they begin to eat.  Mantids typically eat a variety of flies, moths, bees, butterflies, and other insects, but large mantids have even been known to prey upon birds on occasion [Note: it’s pretty gruesome and involves eating brains!].  Mantids aren’t picky eaters, so cannibalism can even be a significant challenge to those trying to raise them.

While uncommon in our area, reports of mantids may continue to increase in the future with climbing temperatures and milder winters—something to keep an eye out for!

 

Signs of Autumn: Orbweavers

Without looking at a calendar, certain things tell you autumn is approaching—pumpkin spice encroaches upon your food and beverage options, weekends are filled with football, the leaves are turning various hues, and brightly-colored orbweaver spiders adorn the landscape.

A beautifully patterned shamrock orbweaver (Araneus trifolium) on the side of a Northwoods cabin. Photo Credit: PJ Liesch, UW Entomology.

Like the overwhelming majority of spiders, the orbweavers (Family Araneidae) of autumn are harmless to humans.  There are a dozen or more common species in the Great Lakes Region and these can be good sized as far as spiders are concerned—easily over 1” long when you include their legs.  Our commonest species are from the genus Araneus and include the cross orbweaver, shamrock orbweaver, and the marbled orbweaver.  They can be quite common in yards, gardens, on plants, and on your back patio.  Other common species in the genus Argiope (the “garden” spiders) are even larger, spanning over 2” with outstretched legs.  In addition to their large size, flashy “fall” colors and patterns conspicuously adorn these spiders—yellows, oranges, reds, stripes, polka-dots, and more.

Despite the large size, orbweaver spiders are harmless. Photo credit: PJ Liesch, UW Entomology.

Their life cycle is another reason why many orbweavers can be so noticeable in autumn.  Our common species overwinter in the egg sac and the young spiderlings usually go unnoticed as they grow and develop the following spring and summer.  By the time they’ve reached maturity in late summer, it’s mating season and the adults have a month or two to go about their business. During that time, they’re easiest to spot sitting in their large circular webs, which were an inspiration for the children’s classic Charlotte’s Web.

Further Reading:
Unfortunately, most folks never take the time to learn about these beautiful and fascinating creatures.  If you ask someone their thoughts of spiders, feelings of fear, disgust, repulsion, and anxiety might come to mind.  In society as a whole, there seems to be a feeling that spiders are something to be loathed or feared, which really shouldn’t be the case. It doesn’t help when the internet has an abundance of myths and preposterous stories about spiders [here’s a good source to debunk some of those myths].  In the grand scheme of things, you’re more likely to be injured by a pet dog than you are to be harmed by a spider.  If anything, spiders should be considered beneficial as they eat an astonishing mass of insects every year.

If you’d like to learn more about spiders, one of my favorite books for the Midwest is Spiders of the Northwoods by Larry Weber.  There are also some great spider blogs out there; my favorites include: SpiderBytes by Catherine Scott and Arthropod Ecology by Chris Buddle. To this day, two of my all-time favorite spider posts are from Chris Buddle’s blog and have the self-explanatory titles of “Spiders do not bite” and “Update: spiders STILL don’t bite”.

Just like Clockwork

We’re all familiar with phenology—that regular progression of plant and animal life through the seasons—to a certain extent.  We might not stop to think about it in detail, but we recognize the crabapples blooming in spring, the fireflies lighting up the nighttime sky in June and July, and the southward flying geese and rutting deer in fall.  When you think of the 25,000+ insects in the Great Lakes Region, there’s a rich diversity of seasonal patterns to pick up on.  Some insect patterns, like cicadas, katydids, and tree crickets calling during the summer months, are hard to miss—although it can be challenging to decipher exactly who’s making that racket (Hint: here’s your translator).  Others are much harder to pick up on unless you’ve been briefed on the subtle clues.  For example, take the tiny foreign grain beetle (Ahasverus advena) which conspicuously pops up in unexpected places in August, September, and October.

To the naked eye, these tiny (1/16 inch long) brownish insects can be a bit tricky to see and it’s hard to tell if they’re beetles, ants, or something else.  Even to budding entomology students pushing the boundaries of what they can interpret under the microscope, foreign grain beetles and relatives might be jokingly referred to as “little brown nothings” and passed over for easier-to-identify specimens.

Foreign Grain Beetles next to a US nickel. Photo credit: PJ Liesch, UW-Entomology.

Around the UW Insect Diagnostic Lab, foreign grain beetles are one of my favorite samples when they arrive in late summer and early fall as they give me the faintest sensation of what it must feel like to be Sherlock Holmes.  Picture a client coming in with a Ziploc bag of tiny brown insects.  After a cursory glance and before the specimens even make it under the microscope, I ask, “are you in a new home by any chance?”  The standard reply is often along the lines of, “Well, yes—but how did you know?”  A quick check under the microscope and the specimen’s identity is confirmed.  It’s elementary, my dear Watson.

Up close view of the Foreign Grain Beetle (Ahasverus advena). Actual size: ~2mm long. Photo credit: PJ Liesch, UW-Entomology.

How is there such a reliable association with an unexpected source: newly constructed homes, where intuition wouldn’t have you expecting insects?  The secret to this seasonal pattern lies in understanding the biology of the foreign grain beetle and its relatives.  These insects love to feed on fungal spores—often in musty stored grains on farms.  It turns out that during the construction of a new home, residual dampness in construction lumber, plaster, sawdust, and other materials can lead to the growth of a trivial amount of mold.  Like vultures to carrion, these beetles fly in looking for a fungal smorgasbord.  Eggs are laid and entire life cycles can be carried out in the wall void of a new home after the drywall, insulation, and siding are put up.

Fast-forward to late summer and just like clockwork the proud new homeowners suddenly have hundreds of tiny brown beetles crawling out through nooks and crannies, causing immediate dismay.  While this can be alarming, these insects are harmless to people, pets, and the home, and are simply a temporary nuisance.  As the construction materials lose that lingering moisture, conditions become unfavorable for the beetles and activity drops off over time.  Pesticides often aren’t needed as the beetles already face an inevitable demise.  Vacuuming or sweeping them up and running a dehumidifier are often the remedy in fall until the dryness of winter puts a final end to the beetle activity.

Department of Entomology

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