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.
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.