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.
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.
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.
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.
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.
If you’ve noticed all the lawn signs for mosquito treatments, you may be wondering if mosquito yard sprays harm other insects. If so, you’re not alone.As an Extension entomologist, this is a common question that I get from the public every year.To get to the bottom of this question, it helps to understand the different types of mosquito spraying that’s done.
One approach (Ultra Low Volume or ULV) is sometimes used by municipalities or abatement districts to control mosquitoes. These ULV applications generally involve using specialized equipment mounted on trucks or aircraft to apply extremely tiny droplets which kill adult mosquitoes by direct contact as the droplets float in the air. Such applications use very small volumes of insecticides either undiluted or with minimal dilution and are often applied after dark when mosquitoes are most active. The microscopic droplets from ULV treatments disperse relatively quickly and have little residual activity—think of them like a “one time strike” to knock down mosquito numbers.
The vast majority of research on mosquito sprays and non-target organisms has looked at these ULV-type treatments. Some good news is that these studies suggest that impacts to non-target insects are relatively small and short-lived.It turns out that the ULV treatments are most effective on insects with very small body mass, so insects larger than mosquitoes tend to be spared.A good summary of the impacts of ULV treatments on non-target organisms can be found in a 2012 review paper by J.A.S. Bonds in Medical and Veterinary Entomology.
Case closed, right?—Not quite. Here in Wisconsin, we don’t really use ULV treatments a whole lot for mosquitoes.The common yard treatments are what we’d call “perimeter”, “barrier”, or “residual” treatments.Such treatments are applied via a backpack sprayer to create a coating or “barrier” on treated surfaces which affects mosquitoes that land on it.These treatments involve applying a residual insecticide (usually from the pyrethroid group) to vegetation in yards and around structures.The pyrethroid products are broad-spectrum and often last for a few weeks or longer depending on the formulation.These same ingredients (and sometimes the exact same products) can also be used to control a wide range of yard, garden, and structural pests (e.g., Japanese beetles, garden pests, household ants, etc.).
While the pyrethroids are very common and widely used for a range of purposes, there’s a knowledge gap when it comes to the impacts of mosquito “barrier” treatments on other insects.While this knowledge gap exists, a few studies raise concerns.One study by Dr. Karen Oberhauser and colleagues found that monarch caterpillars could be harmed or killed even 3 weeks after spraying.A more recent (2022) study by Qualls et al. found that honey bees were harmed 28 days after “barrier” treatments were applied.Thus, if a yard is being sprayed for mosquitoes monthly during the warm season, there are reasons for concern.More research is needed to help understand the effects of these “barrier” yard treatments on insects that often land on vegetation in yards, such as moths, butterflies, fireflies and other beetles, true flies, bees, wasps and other pollinators.
Bonds, J.A.S. 2012. Ultra-low-volume space sprays in mosquito control: a critical review. Medical and Veterinary Entomology. 26: 121-130.
Oberhauser, K.S., Brinda, S.J., Weaver, S., Moon, R.D., Manweiler, S.A., and N. Read. 2006. Growth and Survival of Monarch Butterflies (Lepidoptera: Danaidae) After Exposure to Permethrin Barrier Treatments. Environ. Entomol. 35(6): 1626-1634.
Qualls, W.A., Moser, B.A., Periera, R.M., Xue, R-D, and P.G. Koehler. 2022. Impacts Of Barrier Insecticide Mixtures On Mosquito, Aedes Aegypti And Non-Target Honey Bee, Apis Mellifera. Journal of the Florida Mosquito Control Association 69: 34-42.
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.
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.
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.
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.
If you’re seeing insect damage on your roses this spring, you aren’t alone and there are a number of early-season insect that can catch our attention. For example, a number of caterpillars can occasionally be spotted on roses in spring, such as the rose plume moth (Cnaemidophorusrhododactyla).There’s also the non-native rose leafhopper (Edwardsianarosae) which can cause faint speckling on leaves. Later in the growing season, rose chafers (Macrodactylus subspinosus) and the notorious Japanese beetle (Popilliajaponica) can be a concern.
Perhaps the most noticeable damage to roses in spring is caused by the larvae of sawflies.These insects cause two types of damage: “windowpane” damage when they only feed partway through foliage and leave the upper leaf surface intact or small holes or notches when larger larvae chew entirely through the leaves.In the Midwest, there are three different species of sawflies that can commonly be encountered on roses in spring: the roseslug sawfly (Endelomyiaaethiops), the curled rose sawfly (Allantus cinctus), and the bristly roseslug sawfly (Claudius diffiformis).To the naked eye, the larvae (up to ~ ½ inch long, pale greenish, and caterpillar-like) and the adults (~ ⅓ inch long, dark-colored, and wasp-like) all look similar.However, determining the exact species under magnification can be helpful to understand the potential impacts on your roses.
The roseslug sawfly (Endelomyiaaethiops) is the commonest of the three sawflies that I see samples of at the UW Insect Diagnostic Lab.The larvae of this species have a smooth texture and brownish head capsule; their bodies are translucent and they usually have a pale greenish color due to ingested green leaf material. Some good news about the roseslug sawfly is that this species only has a single generation in spring.Their damage tends to be mostly just a minor cosmetic issue.As the plants really take off in late spring, they tend to “shrug off” this damage and it’s quickly covered up by new growth.
The curled rose sawfly (Allantus cinctus) goes through two generations early in the growing season.Similar to the roseslug sawfly, their feeding damage tends to be minor and plants are usually able to chug along just fine.The larvae of the curled rose sawfly also are pale green with a brownish-orange head capsule.They do have tiny spots on their bodies, but these are only visible under high magnification. This species tends to feed while curled up and they also chew notches on the edges of leaves which can help distinguish this species from the other two sawflies.
The third sawfly commonly seen on roses also tends to be the most problematic—the bristly roseslug sawfly (Claudius diffiformis).Unlike the first two sawflies, this one can continue to reproduce throughout the growing season.Because they go through many generations per year, their damage can accumulate over time and tends to be more notable. Like the other two sawflies, the larvae of this species are also pale green with a brownish head capsule, but they are covered with fine, hair-like bristles when viewed under magnification. Very few sawflies have a hairy or bristly appearance like this, which helps distinguish this species on roses.
If you do bump into these sawflies on your roses in spring, they’re pretty easy to deal with.Options for managing them include:
Do nothing. Since damage from the roseslug and curled rose sawflies tend to be minor, established plants often tolerate these insects with little/no intervention.
Squishing, hand-picking or knocking them into a container of soapy water (be mindful of thorns…)
Insecticidal soap or horticultural oils such as neem oil. Make sure to achieve good spray coverage.
Pyrethrins or spinosad—both are organic spray options. Note that Bacillus thuringiensis kurstaki (which works well against caterpillars) does not work against these sawflies.
Conventional sprays from the hardware store/garden center labelled for use on ornamental shrubs and landscape plants. Use caution since these products tend to have broader-spectrum of activity and can pose greater risks to bees and other pollinators such as butterflies, moths, beetles, and many flies.
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:
The spongy moth, Lymantria dispar has recently been in the news because of its new name. If you haven’t heard of the “spongy moth” before, it’s probably because you learned of this insect as the “gypsy moth”. It’s the same exact creature, just with a new common name.
Why the change?The word “gypsy” in this insect’s name was originally a reference to persons of Romani descent—“the popular name of the gypsy was no doubt suggested by the brown, tanned kind of color of the male” [Forbush & Fernald, 1896]. In 2021, the Entomological Society of America’s Better Common Names Project started to review the common names used to communicate about insects. Common names that include derogatory or inappropriate terms are being assessed. After a lengthy review process, the term “spongy moth” was ultimately decided upon to describe Lymantria dispar—and fittingly so. The beige egg masses of this insect have a soft, spongy consistency. In French-speaking parts of its range, this species has long been known as La Spongieuse for this very reason. Thus, you’ll be hearing more about the “spongy moth” over time as the term “gypsy moth” is phased out from educational/government websites and other resources.
In addition to the name change, the spongy moth should be on our radar for other reasons. Despite being in Wisconsin for decades, this pest can still be a serious defoliator of hardwood trees, both in yards and forested areas. From the period of 2014 – 2020, spongy moths haven’t been much of an issue. An important reason for this is a beneficial fungus known as Entomophaga maimaiga. This fungus was introduced from Japan and it is strongly associated with the spongy moth. Although it took some time to make an impact in the US, this fungus is now viewed as an important “check” on spongy moth populations. Spring rains encourage this fungus, which can cause high mortality amongst spongy moth caterpillars. However, in many parts of Wisconsin we saw an unusually dry year in 2021 which likely curbed the impacts of this fungus. As a result, I saw an increase in cases and reports of spongy moth caterpillars and their damage, adults, and egg masses at the UW Insect Diagnostic Lab last year and Wisconsin also saw a subtle uptick in defoliation of forested areas.
As illustrated in the chart above, spongy moth populations can be very dynamic and can explode under the right conditions—leading to extensive defoliation. The egg-laying strategy of this species plays an important role in this dynamic. Adult female spongy moths deposit egg masses that can easily contain upwards of 1,000 eggs. In late summer and fall of 2021, I saw plenty of reports where trees contained dozens of egg masses, which could turn into tens of thousands of hungry caterpillars this spring.
Luckily, there’s still a bit of time to take advantage of this knowledge as the young caterpillars typically don’t become active until late April or early May. In the meantime, removal or destruction of the egg masses could help reduce local populations. While often found on trees, the egg masses can also be located on just about any surface in a yard—stacked boards, sides of structures, piles of firewood, and even on vehicles. Don’t delay if you noticed spongy moth activity in your area last year, since it won’t be long before the caterpillars are out and active this spring.
Reference: Forbush, E. H. and C.H. Fernald. 1896. The gypsy moth. Porthetria dispar A report of the work of destroying the insect in the commonwealth of Massachusetts, together with an account of its history and habits both in Massachusetts and Europe. Boston, Wright & Potter. 495pp.
Unbeknownst to most students, employees, and visitors at UW-Madison, there’s a room of flesh-eating beetles on campus.An unmarked door on Bascom Hill leads to the chamber more formerly known a the Dermestarium, which serves a rather peculiar yet specific purpose. No need to worry though—this isn’t 1999’s The Mummy. Rather, these insects are actually quite helpful in the way that they’re used.
Most insects are actually helpful in one way or another and provide ecosystem services as pollinators, predators, parasitoids, decomposers, or in other roles.Humans have also figured out some pretty unique ways in which insects can help us out.For example, mealworms can eat and break down certain types of plastics and are being looked at as a way to help reduce man-made waste materials.In the legal realm, knowledge about insects is used to help solve crimes—a field known as forensic entomology, which dates back nearly 1,000 years.In the case of UW-Madison and many other universities and museums, a specific type of beetle is used to help clean skeletal remains for research, teaching, and display in zoological museums.
The beetles in the UW Dermestarium are known as hide beetles (Dermestes maculatus) and they’re especially fond of dried-out, protein-rich materials such as remnants of muscles, sinew, fur, feathers, and similar materials.Out in nature, such insects do play a role in the natural break down of animals remains—but not right away.Rather, much of that initial work is left to the larvae (maggots) of blow flies (Family Calliphoridae) and flesh flies (Family Sarcophagidae).Hide beetles and close relatives from the “carpet beetle” group (Family Dermestidae) show up days, weeks, or even months later once the remains are drier.
In a museum setting, hide beetles can be helpful in the preparation of skeletal remains.With their small size (roughly 1/4-inch long) , these insects use their mandibles to efficiently remove leftover bits of tissue from tiny nooks and crannies.For a human trying to prepare remains, such a task would be tedious and may not be feasible for some structures (such as the inside of a skull).However, a tank of these beetles can easily clean skeletal remains in a matter of days with relatively little effort required, other than maintaining correct ambient conditions for them.
Interestingly, hide beetles and close relatives like the larder beetle (Dermestes lardarius) can be found in our own homes as well.Their presence poses little risk to humans, but could indicate the presence of a dead rodent or bird in a structure.Such insects can also develop on a range of protein-rich materials ranging from dead insects in a window sill to human and pet foods and they can occasionally be a pest in home pantries. Historically, such insects were notable pests of dried meats and cheeses in storage. If you’re curious to know more about these and other insects associated with our homes and everyday lives, Richard Jones has an excellent book on the topic: House Guests, House Pests: A Natural Hisotry of Animals of the Home.
A more detailed history of UW-Madison’s Dermestarium can be found here.
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.
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.
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.
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.
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.
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).
What a year it’s been. Things seemed like they were getting back to normal this past summer, only for the Omicron variant to pop up and say—not so fast. Despite all the ups-and-downs, services have carried on at the UW Insect Diagnostic Lab in one way or another through the second year of the COVID pandemic. Things have changed a bit and these days I’m on campus much more than a year ago. Throughout the pandemic, demand for services at the IDL has remained high with over 2,400 ID requests in 2021.
Since COVID first popped up, there have been some subtle shifts in lab statistics—an increase in the percentage of samples solely involving digital images (vs physical specimens) and an overall increase in the proportion of cases coming from the public. Considering the pandemic, this makes sense. Over the last two years, campus buildings and the IDL have been closed to visitors at various points, meaning that clients couldn’t drop off samples. In other cases, it might have been tough to make it to a post office or the UPS store to ship a sample in. Likewise, with many folks working from home, it likely led to more time out in yards and gardens, or visiting local parks or hiking trails—and more time to notice insects.
Looking back at the cases from this last year, 2021 was a unique year due to our unusually hot and dry weather conditions in Wisconsin. Based on data from the Wisconsin State Climatology Office, Madison was quite warm and saw an extra ~500 growing degree days in 2021, but was down about 15 inches of precipitation for the year. Some parts of the state were even hotter and/or drier than Madison and most of the state was categorized as either unusually dry or in some stage of drought during the year [US Drought Monitor].
The weather conditions this year led to some shifts in the insects and related arthropods seen at the UW Insect Diagnostic Lab. A pest that had been relatively quiet the last decade, Lymantria dispar (formerly known as the “gypsy moth”), thrived with the dry conditions this past spring. In “rainy” years, a beneficial fungus (Entomophaga maimaiga) can “kick in” to help keep their numbers in check. If 2022 is another dry year, we could be in store for even more problems from this invasive species. Certain mites also thrived this year and I saw a large number of cases of eriophyid mites causing damage to plants ranging from coneflowers to garlic. Springtails weren’t necessarily more abundant (they feed on decaying plant matter and thrive under damp conditions), but I suspect the hot & dry conditions sent them looking for any place darker, damper, and cooler. This led to lots of reports as they were trying to invade structures.
We’ll likely continue to see the impacts of the 2021 drought for some time. Plants, including established trees and shrubs, also suffered from the drought and this will likely lead to an increase in reports of “secondary” insect pests in the next few years. Certain insects can be generally “well behaved” and leave healthy plants alone, only to attack stressed and weakened plants. As an example, cases of the two-lined chestnut borer (a notable pest of oaks) often increase 1-3 years after a drought, and I’m expecting to see more cases in the coming years.
In the realm of medical entomology, it was a good year for ticks both in Wisconsin and other parts of the US. Black flies (Family Simuliidae) had another strong year in many parts of the state, although calls about these were shifted a bit earlier than in previous years (likely due to an “early” spring). If there’s a silver lining to the drought, it’s that mosquito pressure was down in Wisconsin for much of the summer. As we received a bit more rain in the latter half of summer we saw some late season activity, but disease pressure remained low (only three West Nile Virus cases in Wisconsin, compared to 50+ in a “bad” year). As recreational and work-related travel increased a bit more in 2021 compared to 2020, I did see an uptick in reports of bed bugs.
With the Asian giant hornet garnering attention in the news for the second year in a row, I continued to see lots of reports of cicada killer wasps, pigeon horntails, great golden digger wasps, and other large insects. Unfortunately, with the sensationalized hype about “murder hornets” (ahem—New York Times…) I had plenty of reports of other large harmless insects that were killed simply because they “looked big and scary” (one particular photo of a tomentose burying beetle comes to mind…). Overall, the Asian giant hornet story was really pretty quiet this year, with a limited amount of activity in a small part of the Pacific Northwest. As of December 2021, the Asian giant hornet has not been found in Wisconsin or anywhere close to us.
I had plenty of reports of social wasps (yellowjackets, bald-faced hornets, and paper wasps) as well as bumble bees this year—including three reports of the endangered rusty-patched bumble bee in the same week in early August! We missed the Brood X “cicada craze” here in Wisconsin, but I still had plenty of questions about them from reporters. We will, however, see some periodical cicadas (Brood XIII) in 2024 in southern Wisconsin.