While scorpions are common in southern parts of the US, they aren’t native to Wisconsin or the Upper Midwest. Occasionally, they show up in the state as hitchhikers from other locations. In the last decade, I’ve seen only a handful of cases where scorpions were spotted in the Badger state. Interestingly, I’ve now had three reports of live scorpions submitted to the UW Insect Diagnostic Lab this year—from Milwaukee, Madison, and recently from Prairie du Chien (as shown in the video clip below). In the rare cases that scorpions do make an appearance, they tend to be the striped bark scorpion (Centruroides vittatus) or a close relative.
The striped bark scorpion is one of the most commonly encountered scorpions in the United States. This arachnid can reach lengths of roughly 2½ inches. It typically has a beige or yellowish body with two dark stripes running down its back—hence the name. They also have a dark triangular pattern near the eyes at the front of the body, which can help distinguish them from other species.
The striped bark scorpion is primarily found in the south-central United States, with most sightings coming from Texas. Its range extends west to New Mexico and eastern Colorado, and as far northeast as the St. Louis area. The species is also present in Mexico. Occasional sightings have been reported outside this typical range. In their natural habitat, these scorpions prefer secluded spots such as under loose tree bark, logs, rocks, and woodpiles. They may also seek shelter near buildings and can inadvertently wander indoors.
A striped bark scorpion found in a home in Prairie du Chien. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.
Like many other scorpions, striped bark scorpions are nocturnal and are mostly active after dark. These arachnids are generalist predators, hunting insects and other small arthropods. They use their pedipalps (“pincers”) and telson (“stinger”) to subdue prey. While technically venomous, the striped bark scorpion’s venom is relatively mild and not considered medically dangerous to humans. However, stings from this species can still be quite painful.
Do the three reports of live scorpions mean that these creatures are becoming more common in our area? No, not necessarily. While it’s hard to tell how the range of scorpions may push northwards with climate change, we’re still well north of the native range of species like the striped bark scorpion. The vast majority of Wisconsinites will never see one of these creatures in the state outside of captivity. If anything, the three cases this year may simply illustrate how scorpions can be moved around by humans under the right conditions.
Each insect species has a “story” to tell—where they came from, what they do, and what their presence means for humans. Knowing this story can make a big difference when it comes to our own actions. For example, imagine finding an insect near your bed. If you recognized the insect as a harmless ground beetle that accidentally snuck in from outdoors, you might shrug your shoulders and carry it outside in a Tupperware. But, if the insect were a blood-feeding bed bug, it could mean an expensive bill to have your home professionally inspected and treated by a pest control company. Knowledge is power!
In my mind, the first step towards getting this knowledge is through proper identification. I say this with a certain amount of endearment, as I am an insect diagnostician after all. However, once you’ve properly identified an insect, it’s easy to look up its “story” (biology, behavior, etc.) in books, websites, or even the scientific literature. This process can allow you to more efficiently identify the root of a problem (if there is one) and figure out a solution.
A cluster fly (Pollenia sp.). These flies are common parasites of earthworms, but frequently enter structures in late summer and can be a nuisance. Preventing their entry into homes is the single most important management step. Photo credit: Katja Schulz, via Wikipedia.
A good example of this concept would be flies in and around homes. There are easily dozens of different types of flies that can be encountered in typical yards and homes in the Midwest and each has a slightly different story to tell. Some can breed in piles of grass clippings or seaweed (e.g., stable flies), some parasitize earthworms but like to sneak indoors (e.g., cluster flies), and others can hitchhike on plants. A common and widespread group of flies is the Family Calliphoridae—the blow flies.
Luckily, blow flies can be identified easily in many cases due to their metallic green or bluish coloration. Some members of this group are even known as “green bottle flies” or “blue bottle flies” due to their distinctive colors. Overall, the blow flies are mid-sized flies and are often slightly larger than house flies (~1/4 – 3/8” long). The larvae are your stereotypical pale and slender “maggots”, although they can be definitively distinguished from similar-looking fly larvae under the microscope.
An adult blow fly. The metallic green coloration is a helpful identifying feature. Finding these indoors often indicates a dead mouse. Photo credit: Brian Gratwicke via Wikipedia.
When blow flies are found indoors, it’s often easy to understand the situation and remedy the problem. One of the biggest factors in the “story” of blow flies is dead stuff. Out in nature, blow flies play an incredibly important role in helping break down dead animal matter. These flies are often the very first insects to show up at dead animals—sometimes within seconds. After laying eggs, the resulting larvae do a lot of work feeding on and breaking down animal tissues. Being poikilothermic (“cold-blooded”), they also develop at a predictable rate depending on the temperature, so these flies are even used to estimate lengths of time in forensic investigations.
There’s always a chance that a blow fly spotted indoors might have accidentally snuck in from outdoors, but in many cases it’s an indication of something dead. Blow flies are able to detect the faint odors of death from long distances, so a single dead mouse, bat, or other creature in a home can attract these flies. Rather than spraying an insecticide, the best remedy is to find the root of the issue and clean it up. In many cases, it’s just a matter of checking mouse traps and discarding the mouse that had recently met its demise.
Another situation that I often see indoors is a scenario that has simply proceeded further than the last one. If an adult female blow fly is able to locate a dead mouse (or other animal) and lay eggs unnoticed, the resulting larvae can consume most of the remains and complete their development. If this happens, the first thing noticeable is often a bunch of maggots wandering the nearby area (the maggots often wander away from their food source when ready to pupate). When they pupate, small brownish “pods” (puparia) may be noticed and upon reaching maturity, dozens of adult blow flies can seemingly appear out of nowhere. In such a case, it’s generally an indicator that a dead mouse or other animal had been present for some time (often a few weeks). Unless there are additional resources for them, these flies usually perish quickly indoors. This scenario frequently comes into play in second homes or cabins that are unoccupied for longer periods of time or if the dead animal is location in a tucked away or inaccessible spot (such as in a wall or ceiling void).
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.
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.
Early 2021—The UW Insect Diagnostic Lab was still mostly closed to visitors at the time. Campus services were mostly back to normal by the start of the fall semester on campus. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.
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].
Drought conditions in Wisconsin as of late December, 2021. It’s been an unusually dry year around the state. Map source: Drought Monitor, UNL.
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.
Insects like the pigeon horntail (Tremex columba) may be large (as far as insects go), but are completely harmless to humans. I saw plenty of cases where members of the public contacted me after killing such insects simply because they looked “big and scary”. When publishers such as the New York Times use sensationalized language (i.e., “murder hornet”) there are plenty of negative impacts. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.
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.
Every year is a bit different here at the UW Insect Diagnostic Lab and 2021 was no exception. I’ll be curious to see what 2022 has in store for insects in Wisconsin!
—PJ Liesch
Director of the University of Wisconsin Insect Diagnostic Lab
On average, I see 2 – 3 new, non-native insect species show up in Wisconsin every year through my work at the UW Insect Diagnostic Lab (3 so far in 2021!). I’ve mentioned this in previous blog posts, but humans make excellent accomplices in moving species from one spot to another on the globe. This last spring, I saw one of the most interesting cases of my career which highlights this point exactly.
Like any good globetrotting adventure, this story involved a rugged, adventurous mode of travel—a Jeep. This particular Jeep had been imported in late 2020 and after a period of time in the eastern US, it eventually wound up in a small town in central Wisconsin. Unbeknownst to the owner of the vehicle, this Jeep also contained unexpected insect stowaways.
These insects managed to survive for months sheltered within the Jeep and would become active when the vehicle was in use—unexpectedly wandering out of nooks and crannies, much to the displeasure of the driver. Obviously, this isn’t something a new car owner wants to see, so a pest control professional was consulted about the insects and they got in touch with me at the UW Insect Diagnostic Lab to figure out what the specimens were. In the initial conversation, the mystery insects had been described as “stink bugs” and I figured that overwintering nuisance insects like the brown marmorated stink bug might have been involved. The photos, however, hinted at something far more puzzling.
The initial photo I received of the mystery insect on a car window. Limited resolution, but definitely not a stink bug or anything else that I recognized. This certainly was a “we’re not in Kansas anymore” type moment.
By this point, I had been running the UW Insect Diagnostic Lab for six years and hadn’t seen anything quite like the insect in the photo. I requested a sample to get to the bottom of this mystery under the microscope. I handle so many cases at the diagnostic lab (~2,500 annually), that I can generally identify most specimens to family (or perhaps even genus or species-level) with a quick peek. In this case I was utterly perplexed, meaning I had to run it through a general family-level taxonomic key for the true bugs (Order Hemiptera). In Borror and DeLong’s Introduction to the Study of Insects the specimens keyed out to the Family Heterograstridae.
From the Hemiptera family key from Borror and DeLong’s Introduction to the Study of Insects. The asterisk symbol (*) is always a surprise.
An asterisk is always a surprise when you encounter it in a taxonomic key. It generally means one of two things: you either took a “wrong turn” in the decision-making process (and misidentified the specimen) or it’s something rare or highly unusual. Something seemed amiss, so I consulted a few other keys to further confirm the Family Heterogastridae. In North America there’s only a single genus (Heterogaster) from this family and three species known from the west coast of the US. The specimens in my possession looked markedly different. Because the Family Heterogastridae is mostly a footnote in the western hemisphere, it’s hard to find information on this group of insects.
This is why geographic clues can be so important in diagnostics and why I request this information with every sample at the UW Insect Diagnostic Lab. Knowing where a specimen was collected and/or originated helps tremendously in learning more about it. Through follow-up conversations, I learned that the Jeep was manufactured in and imported from Melfi, Italy—meaning there was a good chance I was looking in the completely wrong hemisphere for the information needed to identify it.
This led to many evenings of armchair sleuthing. During this process, I’d like to imagine myself as Jason Bourne tracking down members of an international conspiracy while a suspenseful soundtrack blared in the background, but in reality I was mostly just locating pdfs of scientific papers and using Google Translate. Such work could have taken months or even years a few decades ago, but was now possible in the matter of a week or two.
Thanks to Interlibrary Loan and other online resources, I tracked down manuscripts from a half-dozen European and Middle Eastern countries in multiple languages and spent hours pouring over posts on Italian and French insect forums looking for clues. I finally found my answer in a scanned pdf version of Jean Péricart’s Hémiptères Lygaeidae euro-méditerranéens, vol. 1., which identified the specimens as Platyplax inermis—a species associated with Salvia spp. plants in the Mediterranean region.
Map showing reports of Platyplax inermis from its native range. Map credit: iNaturalist.
While most cases at the UW Insect Diagnostic Lab aren’t anywhere near this exciting, even insect diagnosticians get to live vicariously every once in a while.
“Ground bee” season is officially here, but before we get any further, let’s clear up a few things about these insects.Ground-nesting bees get a lot of undeserved blame for stings that they simply aren’t responsible for.Despite their claims, many folks have probably never been stung by an actual “ground bee”.Every year I get plenty of calls about “angry stinging ground bees” in late summer, but these are almost always ground-nesting yellowjackets (Vespula spp.). Undoubtedly, if you stumble into an in-ground yellowjacket nest, you’ll be forced to make a hasty retreat from the area as the colony defends itself.But those aren’t bees…
Entrance of a ground-nesting yellowjacket nest in late summer. These might be black and yellow, but they aren’t bees… Photo credit: Jeff Hahn, U. Minnesota.
While yellowjackets and bees are related (both belong to the insect order Hymenoptera along with the ants and sawflies), they belong to completely different families.From a standpoint of taxonomic classification,mixing up yellowjackets and bees would be like confusing dogs for cats, raccoons, or walruses (all belong to separate families within the mammalian order Carnivora).We do technically have social, ground-nesting bees that can be ornery if disturbed (i.e., bumble bees), but folks generally recognize bumble bees by their large size and robust appearance.
A solitary ground nesting bee guarding the entrance to its nest in a city park in Middleton, WI. Photo credit: PJ Liesch, UW Entomology.
So what about these other “ground bees”? Most bees (about 2/3 of all bees) are actually ground-nesting species. In the Midwest, we’ve got around 500 different bee species, meaning there are hundreds of ground-nesting species around us.Our common ground-nesting bees include species of: cellophane bees, mining bees, squash bees, longhorned bees, sweat bees, and others. For the most part, these ground-nesting bees are solitary creatures that live alone, although many nests can occur in the same general area as shown in the video clip below. They often prefer sunny, open areas with thin ground cover or bare, sandy soil and can be common in parks and home lawns.
To a certain extent, solitary bees can be thought of as the insect equivalent of “preppers”. Each bee digs her own nest—a small, bunker-like tunnel in the ground, which looks like an ant hill.Not only do the females have to construct these shelters, but she has to gather all of the provisions needed for her young to survive inside—often in the matter of just a few weeks.The female bees collect pollen and nectar from flowers to create a nutritious substance called bee bread, which they place into small chambers (cells) and lay an egg. Once the eggs hatch, the young bees (larvae) have all the supplies they’ll need to grow and develop in their survival bunkers.
Most of these ground bees have a single generation per year.The adult bees are out and active for a short period of time (often a few weeks), before they’re done and gone for the year.When they are active, our solitary bees can be excellent pollinators and can be more efficient than honey bees in some regards.However, their pollination services often go unrecognized and unappreciated by the general public.While news articles regularly sound the alarm about honey bee declines, we should really be much more concerned about the potential loss of our solitary bee species, as they’re more sensitive to disturbances, pesticides, and other stressors.
Post-jog entomologist next to five solitary bee nests. These bees are extremely gentle and unlikely to sting. This portion of a local park had thousands of solitary bees flying around. Photo credit: PJ Liesch, UW Entomology.
If you spot ground bees this time of the year, is there any reason for concern? No. Solitary ground-nesting bees are great to have around. Being solitary nesters, these ground bees don’t have a large colony ofadult relatives to defend and they end up being surprisingly gentle and unlikely to sting.Overall, they pose little risk to people or pets.The best thing to do is to simply let them be and appreciate the pollination services they provide.
If you’d like to learn more about Wisconsin’s bees, check on the Wisconsin Bee Identification Guide or the US Forest Service’s Bee Basics: An Introduction to Our Native Bees. If you have solitary ground-nesting bees in your yard and would like to teach others about these amazing pollinators, click the image below to get a sign to laminate and post:
When the COVID situation reared its head back in March of 2020, I wasn’t sure how it would impact activities at the UW Insect Diagnostic Lab.While there was a shift to handling diagnostics mostly remotely, in the end, 2020’s caseload of 2,533 ID requests was just shy of 2019’s all-time record of 2,542 cases.
With Governor Evers’ Stay-at-Home Order last spring, our attentions were occupied by the unraveling pandemic and caseload at the UW Insect Diagnostic Lab was lighter than usual around that time.However, as Wisconsinites shifted to working from home, it meant spending more time in yards and many Wisconsinites pulled out their green thumbs and established COVID “Victory Gardens”.As a result, the diagnostic lab saw a record number of cases in July of 2020, with close to 600 ID requests that month alone.
Monthly caseload at the UW Insect Diagnostic Lab in 2020. Credit: PJ Liesch, UW-Entomology.
Outreach activities of the lab saw a dramatic shift as well.With in-person presentations and workshops off the table, virtual events afforded new opportunities—like a Japanese beetle seminar in July which drew nearly 900 participants. Regular events, like my appearances on WPR’s The Larry Meiller Show also continued through 2020, although I fielded calls from my home’s “reading nook” rather than the WPR studio.
One of the biggest insect stories of 2020 was the Asian giant hornet.Last May we learned that Asian giant hornets had survived the winter in the Pacific Northwest.This of course led to a distinct increase of so-called “sightings” of that insect in Wisconsin, although every “sighting” ended up being common insects from our area. Last year, I saw dozens of ID requests for insects which ended up being look-alikes such as cicada killer wasps, pigeon horntails, and great golden digger wasps.To date, the nearest sighting of the Asian giant hornet is well over 1,000 miles from us here in Wisconsin and poses no immediate threat to the upper Midwest. Further reading:6 Things to Know about the Asian Giant Hornet.
Some invasive pests had big years as well. The viburnum leaf beetle, lily leaf beetle, purple carrot seed moth, and brown marmorated stink bug all increased their footholds in the state. Japanese beetle numbers varied a lot depending on where you were located in Wisconsin. Some areas saw little pressure during droughty periods, while other parts of Wisconsin saw high Japanese beetle activity. Gypsy moths had been quiet in Wisconsin for several years, but increased their numbers last year.I saw a distinct increase of gypsy moth cases in 2020, and I’ll be keeping a close eye on that species in 2021.
Come fall, we saw some stretches of unseasonably pleasant temperatures in October, November, and December.During those periods, multicolored Asian lady beetles—which had been lurking in the background for several years—returned to the spotlight. The multicolored Asian lady beetle activity around Wisconsin was some of the highest of the last decade.Not to be left out of the fun, minute pirate bugs were abundant in some parts of the state and made warm, sunny fall days a little less pleasant due to their biting habits. Speaking of biting insects, black flies were abundant in 2020 and made outdoor activities more challenging in June and July. Mosquito activity varied around the state, although we did see a few cases of the Eastern Equine Encephalitis in 2020.
A female Dryinid wasp. The forelegs are highly modified into scythe-like claws used to grasp other insects. Photo credit: Ty Londo.
No two years are the same at the UW Insect Diagnostic Lab and that includes some of the “X-Files” type cases as well.Some of my favorite cases from 2020 include identifying phorid flies from dead radioactive cats (it’s a long story…), a grim-reaper-esque dryinid wasp, several massive black-witch moths from Central America, and a case involving a black widow spider found in a head of broccoli from the grocery store.Never a dull moment at the UW Insect Diagnostic Lab!
With winter’s arrival, the caseload at the UW Insect Diagnostic Lab is low, although ID requests continue to trickle in. Recently, dark-winged fungus gnats (Family Sciaridae) are one of the commonest insects I’ve seen at the lab. These tiny (1/16 – 1/8 inch long), dark-colored flies are almost always associated with houseplants.
Adult fungus gnat showing the distinctive, curved “Y” fork in the wings. Photo Credit: B. Schoenmakers, via Wikipedia.
Despite their small size, adult fungus gnats can readily be identified by their wing venation. Using a bit of magnification, the translucent wings of these insects possess an oblong, rounded “Y” towards the tips of the wings. While the delicate adults gnats may catch our attention, the larvae are at the root of the problem. The slender, worm-like larvae possess a dark head capsule and live in moist environments.
The connection with houseplants has to do with the feeding habits of the larvae. Fungus gnat larvae generally aren’t plant pests, but scavenge on fungal spores. If the soil of a houseplant is kept too moist, it can create ideal conditions for them. An abundance of fallen decaying plant materials (leaves, etc.) on the soil surface can also contribute. Some of the commonest sources of fungus gnats (and other houseplant pests) are “outdoor” plants which were brought indoors in the fall.
Adult fungus gnats may be a nuisance, but are harmless and short-lived. They will often be observed near potted houseplants (where females can lay eggs) or at nearby windows. When it comes to fungus gnat problems, the following approaches can be helpful:
Sticky card traps can be a useful non-chemical approach for monitoring fungus gnat populations over time and capturing adults. Photo credit: PJ Liesch, UW Entomology.
1) Dry out the Soil: Fungus gnat larvae thrive in damp soil or potting mix. Cutting back on waterings is often the single most important step in dealing with fungus gnats and the mere presence of these gnats is often an indicator of overwatering. Allowing the soil to dry out between waterings decreases survival of the larvae. For succulents and other popular plants that are tolerant of dry conditions, cutting back on waterings can often correct a fungus gnat issue over time without any additional steps.
2) Sticky Card Traps: These traps look like bright yellow index cards, but are covered with a sticky adhesive. When purchased at local hardware stores, garden centers, or online, they usually include small stakes to help place these cards into pots. The adult fungus gnats are attracted to the color of the traps and can become stuck in the adhesive. Used alone, these traps will not eliminate fungus gnats. However, these traps are a non-chemical way to capture adults and can help when used in combination with other approaches. If you have significant fungus gnat numbers, swapping out sticky cards on a regular basis can help monitor for trends over time.
3) Soil Monitoring: If you have lots of houseplants, determining which plant(s) is/are harboring the larvae can be a challenge. One helpful approach is to place slices of potato on the soil surface of potted plants. If larvae are present in a given pot, some may come to the surface to feed on the readily-available starches of the potato. Checking the potato slices for the presence of the dark-headed larvae can help determine where to focus your attention.
4) Cultural Practices: If fungus gnats are really bad, it can sometimes make sense to discard a problematic plant to prevent it from serving as a continual source of fungus gnats. Alternatively, a favorite plant could be washed to bare roots and re-potted in fresh potting mix. When obtaining new plants, it can be helpful to isolate and monitor new plants for fungus gnat or other insect activity before placement amongst other houseplants.
5) Soil Treatments: With severe or persistent infestations of fungus gnats or in cases where watering can’t be reduced, treating the soil is an option to directly target the larvae. The commonest option is to use a product labelled for use on houseplants containing Bacillus thuringiensis israelensis (Bti). These products are based on a naturally-occurring bacteria that is toxic to fly larvae. Such products can be applied as a liquid drench (e.g., Gnatrol) or as granules (e.g., Mosquito Bits) to the soil surface and watered in. Such products won’t eliminate fungus gnats overnight, but can be effective over the course of several weeks.
6) Sprays for Adult Fungus Gnats: Spraying for adult fungus gnats with is not generally effective or recommended. Targeting the adults will only provide temporary relief and it is much more effective in the long-run to target the larvae at the heart of the problem.
With the media craze about “murder hornets” this past spring, I’ve seen a definite increase in reports of Asian giant hornet look-alikes at the UW Insect Diagnostic Lab this summer. Many folks recognize the commonest look-alike in the Midwest, the eastern cicada killer (Sphecius speciosus), which becomes active in July around the time that their prey (cicadas) start emerging. Another look-alike is one that you might not have bumped into before—the great golden digger wasp (Sphex ichneumoneus). Similar to Asian giant hornets, great golden digger wasps are large and nest in the ground, which are reasons why they may be mistaken for the former.
If you haven’t spotted one before, great golden digger wasps can be a bit intimidating in appearance as they can easily be over an inch long. However, their anatomy and appearance are quite different compared to Asian giant hornets. Great golden digger wasps are mostly black with a rusty-reddish color at the base of the gaster (“abdomen”). Their legs are the same reddish color and the black thorax and head possess fine golden setae or “hairs” (hence “golden” in their name). In contrast, Asian giant hornets have distinctive black and yellow stripes on their gaster and a vibrant yellowish-orange head. Great golden digger wasps belong to the “thread-waisted” wasp family (Family Sphecidae) and have a long, slender petiole (“waist”). This isn’t as thin and narrow as the “waist” of the related black and yellow mud dauber (Sceliphron caementarium), but still is quite noticeable when viewed from the side.
Great golden digger wasp (Sphex ichneumoneus); note the slender petiole or “waist”. Photo credit: Judy Gallagher, via Wikipedia.
In terms of their biology, both Asian giant hornets and great golden digger wasps do nest in the ground, but the similarities end there. The Asian giant hornet is really quite similar to our ground-nesting yellowjackets in terms of their nesting behavior. These are social creatures which start nests from scratch in spring and build up in size over the course of the warmer months. Colonies ultimately die out in fall except for the “new” queens which overwinter. With a large colony of relatives to defend, social wasps can be defensive, especially when colonies are at peak size.
In contrast, great golden digger wasps are solitary ground nesters. Without a large colony of relatives to defend, they’re usually non-aggressive and very unlikely to sting. Stings are only likely if one were to pick one up bare-handed—in which case you might be asking for it! Similar to cicada killer wasps, each female great golden digger wasps excavates small tunnels in sandy soil and provisions them with prey for their young to feed on. In the case of the great golden digger wasp, prey consists of katydids, crickets, and relatives from the “grasshopper” group (Order Orthoptera). Rather than kill outright, the females inject their prey with a paralytic “cocktail” to keep them alive and fresh for their young to feed on—what a way to go! In addition to hunting katydids, adult great golden digger wasps visit flowers and can be beneficial pollinators.
Great golden digger wasp (Sphex ichneumoneus) drinking nectar from a flower. Photo credit: Roy Niswanger, via Flickr.
Because they’re unlikely to sting humans, controlling great golden digger wasps is rarely justified and these magnificent creatures can simply be admired. Ultimately, these wasps are strongly associated with sandy soil, so if you see them in your yard every year and would prefer to not have them around, modifying the landscaping may be a long-term option to dissuade them from an area.
Author’s note: As of August 2020, Asian giant hornets have not been found in Wisconsin or anywhere in the Midwest. In North America, these insects are only known from far northwestern Washington state and nearby parts of British Columbia.
See this earlier post for additional details on the Asian giant hornet.
It’s a dark, overcast night as the horde emerges from the nearby woods. There’s no real coordination, but thousands of them—perhaps tens or even hundreds of thousands—seem to wander aimlessly through the yard. Some approach the darkened farmhouse and a few even manage to make it inside…
If this were and episode of The Walking Dead, the protagonists would be in a tough spot, but we’re not talking about zombies in this case. Instead, the topic is millipedes, which have been surprisingly abundant this summer in parts of the Upper Midwest.
Greenhouse Millipede (Oxidus gracilis). Photo Credit: Joseph Berger, Bugwood.org
Most everyone is familiar with millipedes. They technically aren’t insects, but they are related as demonstrated by their segmented legs and “crunchy” exoskeleton (both are types of arthropods). These multi-segmented, worm-like creatures can be common in damp areas and are perhaps most recognizable by their slow walk and their habit of curling into a spiral when disturbed.
Unlike the zombies portrayed in on TV, millipedes are really quite harmless. Some millipede species have been documented as minor crop pests, but in the grand scheme of things, I mostly think of millipedes as being beneficial detritivores. Millipedes feed on decaying plant materials and they return nutrients to the soil. Their feeding also breaks down plant materials into smaller pieces, allowing microbes to more easily assist in the decomposition process. Millipedes can be especially common in damp locations with abundant plant materials: compost piles, rich soil with high organic content, mulch beds, wooded or prairie areas, CRP land, lawns with a heavy thatch layer, and similar.
A millipede curled up in a classic defensive posture to protect its legs. Photo credit: Joseph O’Brien, USDA Forest Service, Bugwood.org
While mostly beneficial, millipedes can occur in very high numbers under the right conditions and can be a nuisance when they seem to suddenly appear in yards and homes. Hopkin and Read’s The Biology of Millipedes (1992) describes situations where massive millipede hordes have covered acre after acre of farmland or stopped trains, quite literally, in their tracks. The Midwest does see large masses of millipedes on occasion and it was a particularly busy year at the UW Insect Diagnostic Lab for calls about these creatures.
The reasons behind millipede mass migrations aren’t fully understood, but moisture is often noted as a common factor. Other potential reasons range from general weather patterns to habitat disruption, competition, and reproduction. When millipedes do move about, many species shun the sun and prefer to move at night or during very overcast days. When they encounter a building, millipedes can sneak inside, although this is really accidental—it’s too dry for them to survive indoors and they typically die within a day or two.
Thousands of millipedes along a resident’s home. From a case submitted to the UW Insect Diagnostic Lab this summer.
Millipedes can be frustrating when mass migrations occur as there’s not much that can be done to completely stop them. It’s not uncommon to have cases where hundreds or thousands of of millipedes crawl onto the foundation or siding of a home every night. If they mostly stay outside, that’s one thing, but this summer I’ve had multiple cases where large numbers of millipedes (hundreds) had snuck under a building’s siding and then rained down through ceiling light fixtures. This sounds like something out of a sci-fi film, but if you were trying to sell your home it could be a real-life nightmare scenario. In such cases, there simply isn’t any way to make the millipedes magically disappear. Insecticides may be tempting but only help to a certain extent because more millipedes can simply show up the next day.
If you’re staring down a millipede horde, one of the most important approaches is physical exclusion. Inspecting the exterior of a home and physically sealing up cracks, crevices, and other potential entrance points with caulk, expanding foam, or new weather stripping can be a chemical free, long-term solution to at least keep millipedes outdoors. Because millipedes prefer damp areas with decaying plant material, keeping landscape pants, fallen leaves, and thick layers of mulch away from the foundation of a home could also help reduce hiding areas for millipedes.
Luckily, millipede mass migrations eventually run their course and quiet down on their own. This year, I saw a spike in millipede reports starting in mid-June and running into early August before subsiding.
