Now that the solar eclipse has passed, the next big natural phenomenon in Wisconsin will be the emergence of Brood XIII periodical cicadas in late May and June. These insects last emerged in the state in 2007 around the time that Steve Jobs was releasing the very first iPhone. While there were some reports of out-of-sync “stragglers” a few years ago, 2024 will be the year of their big emergence. Since these insects emerge every 17 years, you might only have a handful of opportunities to see them in the Badger State in your entire life. Despite having grown up in southeastern Wisconsin and turning 40 next year, I still have not witnessed an emergence myself and I’m really looking forward to this year’s activity.
With all the “buzz” about these amazing insects, I recently developed a new Wisconsin Periodical Cicada Website: cicadas.wisc.edu. This site covers the biology, ecology, and distribution of these insects, with lots of photos, audio recordings, cool historical videos, and other resources.
The recently launched Wisconsin Periodical Cicada Website.
I also wanted to get a clearer picture of where these insects occur in Wisconsin. This winter, I dug through 150+ years of books, newspaper columns, university and government reports, and specimens in our very own Wisconsin Insect Research Collection to develop an updated map for the state. While this map is an improvement over older ones, there’s still plenty to learn about the local distribution of these cicadas in Wisconsin. To that end, I also launched a community science project on the website for participants to submit their own sightings from the state. It’s a brief fillable form and photos can be uploaded right from your phone, tablet, or computer—no app required. I’d love to receive any reports of periodical cicadas from Wisconsin this year to help improve our map of them in the state.
If you’re a cicada enthusiast and have a lot of reports to share, feel free to contact me via email (pliesch@wisc.edu) to discuss other arrangements. If you’re unsure if you’ve spotted a periodical cicada, check out the website’s Cicada Basics page or reach out for assistance at the UW Insect Diagnostic Lab.
Adult periodical cicada. Photo credit: USGS Native Bee Inventory and Monitoring Program; public domain image.
Lastly, if you’re hoping to see and experience the periodical cicadas for yourself, your best bet would be to visit the Lake Geneva area in June. This part of the state has a very long and well-established history of periodical cicada activity. There’s also an updated Wisconsin map and a summary for each county on the periodical cicada website’s When and Where page. Previously, much of this information was buried in the literature, so the Wisconsin Periodical Cicada Website offers a unique look at the known distribution of these insects in the Badger State.
Check out cicadas.wisc.edu for additional details and get ready for all the buzz this spring!
As one of the coordinators of Wisconsin Insect Fest, I’m thrilled to announce that Insect Fest will be back this year and is coming to the Upham Woods Outdoor Learning Center (Wisconsin Dells) this August. The event will be held from 2–10 PM on Saturday, August 19th, 2023 and is free and open to the public. A family-style cookout will be provided to participants (please RSVP if interested). Insect enthusiasts of all ages are welcome to attend!
Wisconsin Insect Fest is a celebration of insects and attendees will have the opportunity to learn about the different types of insects found in Wisconsin and the many important roles they play in the environment. Insect Fest will feature a variety of indoor and outdoor activities suitable for insect enthusiasts of all ages, including educational presentations, hands-on activities, guided insect hikes, live insects, and an informal BioBlitz activity. This is also a great opportunity to meet entomologists and learn about what they do.
The Wisconsin Insect Fest is a family-friendly event, and we encourage everyone to attend and learn about the fascinating world of insects. We hope to see you there!
Spongy moth (Lymantriadispar) season has officially begun here in Wisconsin. Earlier this week (May 3rd), the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) Pest Survey Program reported caterpillars emerging from an egg mass in far southwestern Wisconsin. Based on forecasting models from the USA Plant Phenology Network, we should expect to see caterpillar emergence begin across much of southern Wisconsin over the next week. As things continue to warm up, the pattern will push further north in the state.
Forecasting map from USA National Phenology Network for predicting hatching of Spongy Moth eggs. Source: USA-NPN (www.usanpn.org)
We may be facing a challenging year from this invasive insect. Dry conditions suppressed a beneficial fungal disease (Entomophagamaimaiga) the last two years and allowed spongy moth populations to build up. Along these lines, DATCP reported a 102% increase in male spongy moths caught in trapping surveys last year. Likewise, the Wisconsin Department of Natural Resources (DNR) Forest Health Team reported a significant uptick in defoliation last year—from 294 acres defoliated in 2021 to over 85,000 acres defoliated in 2022.
At this point in the season, it’s hard to know how much damage will ultimately occur on yard and forest trees in 2023. However, you can get an estimate of potential defoliation in your own yard by counting egg masses. Each overwintered spongy moth egg mass contains upwards of 1,000 eggs, so a yard with dozens of egg masses could soon face tens of thousands of hungry caterpillars in the near future.
Dozens of spongy moth egg masses on a tree trunk. Photo credit: Karla Salp, Washington State Dept. Agriculture via Bugwood.
Over the next few weeks, we can expect spongy moth caterpillar activity increase. These small caterpillars will cause a trivial amount of damage at first but will gradually become larger, hungrier, and more damaging over time. Keep an eye out for activity in your yard. If you are inundated with caterpillars, consider using sticky barrier bands and burlap barrier bands to trap them as described on the UW-Madison Extension Spongy Moth website.
Looking at the bigger picture, Mother Nature could hold a trump card for our spongy moth situation. If we end up having a rainy spring, damp conditions could encourage the fungal disease Entomophaga maimaiga to kick in and crash spongy moth populations (this halted outbreaks in SE Wisconsin in 2004 and 2010) . However, if we experience another dry season, it could allow spongy moth populations to build further—stay tuned and hope for rain!
When most folks think of “cutworms” they probably envision big fat caterpillars munching on plants in their yards and gardens. Sure enough, we have many species from the cutworm & armyworm family (Family Noctuidae) that can be notable crop pests, such as black cutworm, bronzed cutworm, variegated cutworm, true armyworm, fall armyworm, and others. Readers should keep in mind that the Family Noctuidae is surprisingly diverse with over 2,500 species known from the US and Canada. Many of these species play important roles in the food web and can be as important as bees for pollination of certain crops!
While cutworms can be common during the summer months into the fall, we usually don’t expect to see them this time of the year. Surprisingly, there’s one cold-hardy species that has been common in Wisconsin recently—the “winter cutworm” (Noctua pronuba). This species gets its name due to the fact that the caterpillars are cold-tolerant and can be active when temperatures dip. While they won’t be out-and-about during a polar vortex, I’ve had many recent reports at the UW Insect Diagnostic Lab of winter cutworm caterpillars wandering on the snow when temperatures have been in the 20’s. Overall, there are very few caterpillars that venture onto the snow, period.
Winter cutworm caterpillar wandering on the snow. Photo submitted to UW Insect Diagnostic Lab in late 2022.
Similar to other cutworms, the winter cutworms are plump, earth-toned caterpillars—they are brownish with pairs of black dashes bordered by white running down the sides of their backside, which makes them easy to identify. (Technically, a greenish form of the caterpillars also occurs). In addition, if you see any caterpillar that even looks “cutworm-like” out on the snow, it’s almost certainly this species. They pass through the the winter as nearly-mature caterpillars before pupating in the spring. The adult moths are active during the warmer months and display an amazing array of different color forms—ranging from very light beige to grey or brownish—although the hindwings (typically tucked under the body at rest) are a diagnostic yellow color. Thus, adults are commonly known as “large yellow underwing” moths.
Larger yellow underwing moth showing the distinctive yellow color of the hindwings. Photo credit: Olaf Leillinger via Wikipedia CC.
The winter cutwormcan be found from coast-to-coast in much of the US and Canada, although this wasn’t always the case. This species is common in Europe and wasn’t known from North America until 1979 when it was first spotted in Nova Scotia. While the caterpillars do feed on a wide range of plants, they’re rarely a notable pest. Outbreaks and reports of damage aren’t common, although there was a notable outbreak in Michigan around 2007-2008. In most cases, these caterpillars are simply a curiosity as they wander across the snow on mild winter days—sometimes by the thousands. In addition, winter cutworms can occasionally sneak into structures as well, which can be another surprise to see caterpillars actiely wandering in garages or barns when the temperature is in the 40’s.
Winter cutworm caterpillar found in a garage last December. Photo submitted to UW Insect Diagnostic Lab.
If you’re like me, you’ve probably been out appreciating our recent fall weather.Likewise, boxelder bugs (Boisea trivitatta) have also been enjoying the warmth.I’ve seen an uptick in reports of boxelder bugs at the UW Insect Diagnostic Lab this year compared to most other years in the last decade and weather patterns in the Midwest have played an important role.
Adult boxelder bug (Boisea trivitatta) on the side of a building. Photo credit: PJ Liesch, UW-Entomology.
Whether you recognize them or not, there’s a good chance you’ve bumped into boxelder bugs before.These black and red insects can be common throughout the warmer months and can be especially abundant in late summer and early fall.Adults are approximately ½ inch long and have a criss-cross pattern on their backside created by their wings.Juveniles (nymphs) are smaller with much more red on their bodies.As the nymphs mature, their developing black wing pads become noticeable.True to their name, boxelder bugs are commonly associated with boxelder trees (Acernegundo).Botanically speaking, boxelders are technically a type of maple, and some other maples can also be a host for these insects as well as ash trees and a few others.
Boxelder bug nymphs (juveniles) on the UW-Madison campus. Photo credit: PJ Liesch, UW Entomology.
From a plant-health perspective, boxelder bugs cause little damage to plants and are of little concern.These insects get the most attention when they’re spotted on the sides of homes and other structures.They’re often particularly fond of the southern and western sides of homes where the warm afternoon sun hits.Boxelder bugs are often spotted on buildings in fall as they search for sheltered overwintering spots.If they can squeeze in through a gap or crack, they can easily hunker down in a wall void, or similar spot for the winter.Sometimes, boxelder bugs can make it to a location where they become active indoors during the winter months, much to the chagrin of the humans living in the home.While these insects can be perceived as a nuisance, they’re really quite harmless to people, pets, and homes (although they could stain light-colored fabrics if crushed).Like other “fall invading” insects (e.g., cluster flies, multicolored Asian lady beetles, brown marmorated stink bugs, and western conifer seed bugs), a helpful approach is to seal up potential entry points on the exterior of your home before these insects make their way inside.
Boxelder bugs congregating on the side of a home. Photo submitted to UW Insect Diagnostic Lab.
Looking at long-term patterns, boxelder bug populations have generally been low in many parts of Wisconsin over the last decade.A reason for this is moisture.When we have rainy years, entomopathogens (insect-infecting pathogens) can keep boxelder bug populations low.In contrast, boxelder bugs tend to thrive under drier and warmer conditions.There’s even been research on a closely-related species (the western boxelder bug, Boisea rubrolineata)in the western US suggesting that those insects deliberately sunbathe and secrete a chemical to help inhibit the common entomopathogenic fungus Beauveria bassiana.Here in Wisconsin 2021 was surprisingly dry in many areas which likely helped boost boxelder bug numbers.Likewise, some parts of Wisconsin also saw dry conditions continue into 2022, which may have helped them further, leading to an increase in boxelder bug populations and reports this year.
With the arrival of fall, we’re starting to see pumpkins, spooky yard decorations, and pumpkin spiced everything (*shudder*). Not to be left out of the festivities, one insect can be quite noticeable this time of the year—the large milkweed bug (Oncopeltus fasciatus).
If you’re wondering, we do also have a small milkweed bugs (Lygaeus kalmii), although it’s not usually as common as the ubiquitous, larger cousin. Both juveniles (nymphs) and adults of the large milkweed bug are fittingly adorned for fall. Adults reach lengths of nearly 3/4 inch long and are mostly orange with black patches on the wings and body. Going through “simple metamorphosis” (technically, they’re paurometabolous), the juveniles or nymphs look similar in body shape to adults (although smaller) and are also orange with some black. In more mature nymphs, the developing blackish wing pads are quite noticeable. When you see a group of nymphs and adults hanging out on milkweed in the fall, it’s easy to recognize that they’re all the same species.
Large milkweed bugs specialize on milkweed plants and are one of the many creatures that can be found in and around milkweed patches. When they feed, large milkweed bugs use their sucking-type mouthparts to sip fluids from plants; they’re especially fond of the developing seed pods and are often spotted on pods. While home gardeners hoping to rear monarchs might be concerned about competition, these insects generally cause little harm to plants and are more of a curiosity than a pest.
Group of large milkweed bugs (Oncopeltus fasciatus) on milkweed at UW-Madison; both adults and nymphs are present. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.
Large milkweed bugs have a very seasonal pattern in the upper Midwest. They can’t survive the winter at more northern latitudes, so they must migrate northwards each year. Here in Wisconsin, you’d be hard pressed to find large milkweed bugs in spring, but by July they’ve often arrived in low numbers. Large milkweed bugs can become quite common by late summer and early fall as it typically takes 40+ days for a new generation of adults to appear from eggs laid in our area.
In much of Wisconsin, we’re just starting to see foliage change to reds, oranges, and yellows, but as you’re out enjoying the fall weather, keep an eye out for these festive-looking insects around milkweed patches.
If you’ve spotted small, crunchy beetles in your home this summer you aren’t alone. Broad-nosed weevils (Curculionidae: Entiminae) have been a surprise this summer at the UW Insect Diagnostic Lab. While I see cases of these insects every year, things have been a bit more intense this summer with a flood of reports from around Wisconsin.
What’s a weevil? Out of the 100+ different families of beetles, the weevils (Family Curculionidae) are extremely diverse with over 50,000 species in this group alone. In terms of their appearance, most weevils might remind you of Gonzo from the Muppets with their very pronounced “snouts”. A great example of this in Wisconsin is the genus Curculio (the “nut and acorn weevils”). Some species in this group can have a snout (technically “rostrum”) as long as the rest of their body.
The pecan weevil (Curculio caryae). The pronounced rostrum or “snout” is a classic feature of many members of the weevil family. Photo credit: Jennifer C. Girón, Museum of Texas Tech University. Bugwood.org.
On the other hand, some members of the weevil family lack the pronounced snout . One such group, the subfamily Entiminae, is commonly referred to as the broad-nosed weevils. Our common broad-nosed weevils tend to be small (around ⅛ – ¼ inch-long) and have pear-shaped bodies with very hard, crunchy exoskeletons; they also have “elbowed” antennae similar to ants. The color of the broad-nosed weevils can vary by species, but many are blackish or grayish.
The imported longhorned weevil (Calomycterus setarius)—a type of “broad-nosed weevil” that occasionally sneaks indoors. Photo credit: Natasha Wright, Braman Termite & Pest Elimination, Bugwood.org
When it comes to broad-nosed weevils, we have over 100 species in the Midwest alone. In general, these are “outdoor” species associated with plants. The larvae tend to feed on the roots of plants while the adults often chew small notches out of the edges of foliage. Interestingly, a few species in this group have the habit of sneaking indoors during the summer months. Once inside, these insects are completely harmless but can be a minor nuisance as they seem to mindlessly wander on walls or floors.
During the summer months, some broad-nosed weevils can sneak indoors—occasionally in large numbers. In this case, hundreds of strawberry root weevils (Otiorhynchus ovatus) were wandering on the side of a home. Photo submitted to UW Insect Diagnostic Lab.
Conditions in Wisconsin over the last year and a half must have been just right for some of these species, since I’ve had a flood of requests to help identify broad-nosed weevils in homes and other structures during the summer of 2022. Often when I see “weevil” cases it’ll be a handful of weevils indoors, but this year I’ve also seen plenty of reports of large numbers of weevils (hundreds or thousands!). The top three species I’ve been seeing in Wisconsin have been the strawberry root weevil (Otiorhynchus ovatus), the imported longhorn weevil (Calomycterussetarius), and the black vine weevil (Otiorhynchus sulcatus). There are a number of other species in this group that can invade structures as well. Due to the similar appearance of these beetles, it’s often necessary to get a sample under the microscope to help confirm the exact species. If you come across broad-nosed weevils in your home and want to know the exact type, feel free to send in a sample to the UW Insect Diagnostic Lab: insectlab.russell.wisc.edu/samples.
While these weevils can be a bit of a nuisance, there usually isn’t much of a need to spray (especially indoors). In the grand scheme of things, good physical exclusion (i.e., sealing things up better with caulk, expanding insulation foam, better weatherstripping, etc.) can go a long way to help prevent broad-nosed weevils from getting indoors in the first place. For the weevils that do make it indoors, insecticide really aren’t necessary and sweeping or vacuuming up these slow-moving pests is the best course of action.
Heading into the growing season, spongy moth (Lymantria dispar, formerly known as the “gypsy moth”) was poised to have a big year in Wisconsin.That prediction has held up and I’ve seen an influx of reports of spongy moth caterpillars and damage at the UW Insect Diagnostic Lab (IDL) this spring.In some areas, these caterpillars are causing conspicuous damage, which has also led to a flurry of questions from the public on what to do about them.Let’s take a look at how this season has shaped up, how the next few weeks could turn out, and what can be done.
What’s happened so far (as of mid-June)?
After a cool start to spring, we saw some unseasonably warm temperatures during the second week of May, which jump-started a lot of insect activity.I saw a distinct increase in diagnostic requests at the IDL around this time as well as my first reports of spongy moth caterpillars.
Unseasonably warm temperatures (90+˚F) for Madison, WI in early/mid May kicked off a lot of insect activity. Source: Weather Underground.
Initial sightings of small caterpillars mostly involved larvae dangling from trees and structures from silken threads—a dispersal mechanism down as “ballooning”.In other cases, thousands of tiny, dark caterpillars stood out against light-colored siding of homes. At first, these tiny caterpillars couldn’t cause much damage—with their small size, they simply don’t eat much.It isn’t until caterpillars are larger and more mature that they really start to chow down and damage increases dramatically. It’s estimated that 80-90% of the damage caused by these caterpillars is from the final two larval substages (instars). Reports of notable damage started to pop up a few weeks later in early June.
Based on the reports coming in to the UW Insect Diagnostic Lab, the heaviest spongy moth activity in 2022 spans from southeastern Wisconsin (Lake Geneva area) west through Rock, Green, and Dane Counties, and north to Sauk, Juneau and Monroe Counties.Overall, Dane and Walworth Counties stand out for the number of spongy moth sightings and reports of damage that I’ve received.
What will the next few weeks be like?
The end of caterpillar activity is in sight—but we’re not there yet.I’m still getting reports of spongy moth caterpillars and likely will for a few more weeks.In many cases, the caterpillars being spotted are now pretty large (1¾– 2 inches), meaning that they’re feeding voraciously and causing lots of damage to plants. If there’s a silver lining, it’s that these large caterpillars should also be pupating in the near future—putting an end to their damage for the season. However, I’ve been receiving reports of mixed caterpillar sizes, with some caterpillars only measuring ¾ – 1 inch long.These smaller “stragglers” will continue to feed and cause damage into July, meaning we’re not entirely out of the woods yet.
A large spongy moth caterpillar showing the distinctive color pattern (click for larger view). The larger, more mature caterpillars cause the bulk of the feeding damage. Photo credit: PJ Liesch, UW Insect Diagnostic Lab
Another variable that could be at play this year is a beneficial fungus known asEntomophaga maimaiga.This disease can specifically infect and kill spongy moth caterpillars and can play an important role in regulating their populations over time.Last year’s drought likely helped set the stage for 2022 by suppressing this beneficial fungus. This spring we’ve had pretty regular precipitation in many parts of the Midwest, which could help put a dent in spongy moth populations if this pathogen kicks in.
What can be done about spongy moth?
This has been one of the commonest questions I’ve been getting recently and have seen plenty of posts on social media sites like Facebook and Nextdoor asking this same question. Management of spongy moth really depends on the life stage of the insect. The UW-Madison Division of Extension Spongy Moth website has an excellent month-by-month discussion of management approaches.
For small numbers of yard trees, the burlap band method can be a way to remove larger caterpillars from the equation.However, it’s important to understand that this method can be time and labor intensive as you need to check bands daily and brush caterpillars into a container of soapy water to maximize effectiveness. [Note: don’t touch the caterpillars bare-handed, it hurts!].For large trees, there’s not much else that an individual homeowner can do other than discussing chemical treatment options with an arborist. Many of the online posts I’ve seen have had an element of panic, but it’s also important to keep in mind that trees that are in otherwise good health can generally tolerate defoliation and will push out another batch of leaves later this year.I start to worry more about plant health when trees are defoliated repeatedly, as that can lead to secondary issues over time.
Burlap band around an oak tree. Large spongy moth caterpillars feed mostly at night, so burlap bands offer a convenient daytime hiding spot. Caterpillars can then be brushed into a container of soapy water. Photo credit: Bill McNee, WI-DNR.
I’ve also seen a number of questions about aerial sprays for spongy moth.This year, the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) has been coordinating aerial spraying in the western parts of the state to slow the overall spread of this invasive species.The treatment used in early-season aerial sprays (Bacillus thuringiensis kurstaki) is most effective against small caterpillars. Later spraying will focus on disrupting the ability of adult moths to successfully find a mate. In theory, members of the public could band together to coordinate aerial spraying in their local area, but the planning process for this can take months.By the time folks were posting on social media expressing a desire for aerial treatments in their neighborhood, that option was no longer feasible.
One key thing to pay attention to later this summer will be the egg masses laid by adult female spongy moths. Each egg mass can contain upwards of 1,000 eggs, so surveying for egg masses can give insight into what the spongy moth situation could be like in 2023. Those egg masses will also remain in place for roughly nine months until they hatch next spring, which gives lots of time for a search-and-destroy scavenger hunt in your yard.
For additional information on managing spongy moths, check out the updated UW-Madison Division of Extension factsheet on this insect and the Extension spongy moth website with month-by-month recommendations.
The United States Department of Agriculture (USDA) declared April to be Invasive Plant Pest and Disease Awareness Month. To support this effort, the University of Wisconsin Insect Diagnostic Lab recently launched a new Wisconsin invasive insect mapping page to help track invasive insects in the state.
If you’ve followed this blog for a while, you’ll notice that quite a few of my posts focus on invasive insects. Why? In part, it’s because these non-native insects tend to be new or emerging issues and a key role of the UW Insect Diagnostic Lab is to help identify and track new and trending insects in the state. In addition, these invasive insects can sometimes cause significant damage or capture our attention for other reasons. In a typical year, I see 2-3 new non-native insects show up in Wisconsin, which really adds up over time. For every species that has arrived here, many more are making progress towards the state (e.g.,spotted lanternfly). In other cases, non-native insects show up completely out of the blue.
What’s the big deal with non-native insects?
Non-native insects can cause harm in many different ways:
Be an aesthetic or nuisance issue (e.g., European earwigs, German yellowjackets, etc.)
Introducing the new mapping page:
Because of the impacts mentioned above, it’s helpful to track invasive species so we can better understand where they may be having impacts, and also to get the word out about new detections and allow folks to take appropriate action. To help in this regard, the IDL’s new invasive insect mapping page hosts a series of maps showing the known county-level distributions of a select list of invasive species.
These particular species have been included due to their relatively recent arrival in Wisconsin, and the ability to track them on a county-by-county basis. Keep in mind that many other non-native insects can be found in the state, but some of these have been around a long time, are now widespread, and tracking on a county-by-county basis is no longer feasible or helpful (e.g., Japanese beetle, European paper wasps, German yellowjackets, European earwigs, and many more).
The maps on this page will be updated when new detections occur, and additional species maps will be added over time. If you believe that you’ve observed one of the listed insects in a county where it has not been documented or a new invasive insect species, please collect evidence (physical specimens and/or digital images) and contact me to work on officially confirming the detection. An example entry from the map page can be found below:
Example entry from the new Wisconsin Invasive Insects Mapping page
Despite the season, there’s a surprising number of insects and related arthropods that can be found on the snow during the winter months here in the Midwest.Such creatures have fascinating life histories and special adaptations (such as natural “antifreeze”or cryoprotectants) that allow them to not only survive, but remain active at low temperatures.Even these adaptations have limitations and winter insects generally aren’t active if temperatures are below ~20˚F (-7˚C).Most activity occurs on mild winter days when temps close to or just above freezing.
If you’re curious to learn more about the stories behind these winter creatures and others, I’d encourage you to check out Bernd Heinrich’s Winter World: The Ingenuity of Animal Survival. Read on to learn about some of our commonest “winter” insects in Wisconsin and nearby states:
Snow Fleas: If you follow this blog, you might recall the example of snow fleas from two winters ago.These dark-colored springtails (Collembola) can sometimes be abundant enough to give large swaths of snow a sooty appearance.Snow fleas can be common on mild winter days and if I’m out cross-country skiing in the Northwoods, I’m often more surprised if I don’t spot any.
Up-Close View of a Snow Flea. Photo Credit: Daniel Tompkins via Wikipedia
Snow Flies: One of the weirdest examples of a “winter” insect would be “snow flies” from the genus Chionea. Despite their spider-like appearance, snow flies are actually a type of wingless Limoniidcrane fly.Being wingless and generally slow moving might sound like an easy target for predators, but by being active at cold temperatures these insects can actually avoid the many predators that feed upon related flies during the warmer months.Interestingly, their physiology is so specialized, that these unusual insects can be active between about 20˚F (-7˚C) and 32˚F (0˚C), but if it’s a warm winter day with melting snow it can actually be too hot for them!If you’d like a more detailed look at these insects, check out J.R. Schock’s article in The Kansas School Naturalist.
Snow fly (Chionea sp.) on the snow in northern Wisconsin. Photo credit: PJ Liesch, UW Insect Diagnostic Lab
Winter Crane Flies: I occasionally get reports of “swarming mosquitoes” on winter days, and perhaps you’ve bumped into a cloud of tiny delicate flies out in the snowy woods or on a mild fall or spring day.What you’ve likely encountered are winter crane flies (Family Trichoceridae).These delicate flies are related to mosquitoes but have no interest in blood.The adults are simply trying to mate and the larvae are scavengers.
A winter crane fly (Family trichoceridae) that landed on the snow. These can be spotted flying on mild fall, winter, and early spring days. Photo credit: PJ Liesch, UW Insect Diagnostic Lab
Snow Scorpionflies: In my mind, one of the more elusive winter insects is the snow scorpionfly.Despite having “scorpion” in the name, these aren’t scorpions (or true flies for that matter).Rather, they belong to a small order of insects (Mecoptera), which includes some bizarre examples, such as the common scorpionflies, hangingflies, and earwigflies.Like the snow flies, the snow scorpionflies are also flightless and simply wander about on the snow when conditions are right.In the Midwest, we only have two species from this group Boreus brumalis and Boreus nivoriundus, and both species are associated with mosses.
A snow scorpionfly. Elusive, but fascinating creatures. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.
Aquatic insects: If you’re near open streams or rivers during the winter months, certain aquatic insects can sometimes emerge and be found on the snow. Caddisflies and stoneflies are two of the commonest examples. I recall ice climbing one winter’s night at Governor Dodge State Park west of Madison and reaching the top of a frozen waterfall only to spot dozens of adult “aquatic” insects active on the snow.The conditions must have been just right that evening, as I also saw hundreds of tiny Cynipid wasps (from oak galls) on the snow as I descended the access trail from the climb.
Caddisfly on the snow near a Northwoods stream. Photo credit: PJ Liesch, UW Insect Diagnostic Lab
Spiders: Hexapods aren’t the only arthropods getting in on the winter fun.Species from at least a half-dozen families of spiders can occasionally be spotted on the snow on mild winter days.They might be pretty lethargic, but it’s still interesting to see creatures like that out-and-about on the snow. The video clip below shows a spider I spotted on the snow in Northern Wisconsin on New Year’s Eve a few years ago when the air temperature was right around 30˚F (-1˚C).
