Extensioneers have been receiving reports of fall home invaders trickling into Ohio homes. However, the predicted weather conditions for this coming weekend and early next week could turn the trickle of insects into a flood, particularly in the southwest part of the state.
Boxelder Bugs (Boisea trivittata, family Rhopalidae) have long been the “poster child” for insects that invade homes and other structures in the fall. Thanks to a tip from a BYGL reader, for the past three days, I’ve been taking pictures of a sizable aggregation of boxelder bugs on the trunk of a boxelder (Acer negundo, family Sapindaceae) in southwest Ohio. It’s the first sign that the bugs are planning a little breaking and entering.
Boxelder bugs range in size from 1/2" - 3/4" long. They are narrow-shaped, flat-backed, and dark gray or dark brownish-black. The bugs have three highly visible orangish-red stripes running lengthwise on the pronotum, the area behind the head; "trivittata" is Latin for "three-striped".
The bugs are seed-feeders and are so-named because of a strong association with their namesake host, but only female trees. Boxelder is dioecious (= “two houses”) which means individual trees either produce male or female flowers, but not both. Research has shown that boxelder bugs will only gather in large numbers on female boxelder trees, but not male trees.
However, adults and nymphs will commonly use their piercing-sucking mouthparts to draw juices from the seeds of other trees in the Acer genus as well as ash (Fraxinus spp.). They have also been observed feeding on alder, apple, buckeye, cactus, geranium, grape, honeysuckle, lilac, linden, oak, peach, plum, spirea, strawberry, and tulip. I'm aware of boxelder trees being cut down in an attempt to eliminate the bugs; however, their wide-ranging feeding activity illustrates why this management effort may fail.
Boxelder bugs have one generation in colder climates, and two generations in warmer climates. Regardless, they end the season as a mix of adults and immatures (= nymphs). However, only the adults can make it through the winter which presents a challenge to the nymphs.
At this time of the year, only late instar nymphs have a chance to make it to adulthood and thus survive the winter. To hasten their development by acquiring a quick energy boost, late-instar nymphs commonly attack and suck the life out of earlier instar nymphs. It’s a true Halloween horror story!
Boxelder bug aggregations on tree trunks occur during cold snaps in early fall. They collect on the west side of the trunks to maximize exposure to warming by solar radiation.
However, if a cold snap is followed by a warm spell, the adult bugs use their wings to disperse in search of suitable overwintering sites which may include homes or other structures. Of course, the wingless nymphs are left behind to suffer their freezing fate.
Boxelder bugs may also be joined by other fall home invaders including Western Conifer Seed Bugs (Leptoglossus occidentalis, family Coreidae) and Magnolia Seed Bugs (L. fulvicornis). These are called “leaffooted” bugs owing to the leaf-like structure on the tibia of their hind legs.
More notorious fall home invaders include Multicolored Asian Lady Beetles (Harmonia axyridis, family Coccinellidae) and Brown Marmorated Stink Bugs (Halyomorpha halys, family Pentatomidae). Both of these non-natives have a deserved reputation for invading homes in huge numbers. Although they’ve been somewhat quiet in recent years, there’s no predicting when or where we will see outbreaks which are usually highly localized.
On a side note, the predatory behavior of multicolored Asian lady beetles has helped them to redeem their reputation to some degree. Adults as well as the alligator-like larvae are commonly observed consuming aphids and other plant-sucking insects.
The stink bugs, on the other hand, remain villainous. Outdoors, they damage fruit and vegetables. Indoors, they buzz around to scare the bejeebers out of homeowners, children, pets, etc.
Why Do They Break Into Homes?
Insects that invade homes and other structures in the fall do not intend to make their way into heated interior spaces. In fact, they are doomed if this happens.
Insects are “cold-blooded” (exothermic) meaning the speed of their metabolism is mostly governed by ambient temperature. The higher the temperature, the faster their metabolism, and the faster they "burn" fat. Yes, insects have fat, but it's confined within their hard exoskeletons, so they don't suffer embarrassing expanding waistlines.
We are endotherms (warm-blooded) meaning we can generate internal heat to maintain a constant internal temperature. Of course, an exothermic physiology has some benefits. Imagine losing weight just by laying out on a sunny beach.
The home invaders feed voraciously in late summer to accumulate fat. They then seek sheltered locations in the fall where cool temperatures slow their metabolism during the winter so they will not exhaust their stored fat reserves. This survival strategy keeps them alive since there is nothing for them to eat throughout the winter.
Home-invading insects are attracted to the solar heat radiating from southern or western-facing roofs and outside walls and the warmth radiating from within. This can lead them into attics, exterior wall voids, and spaces around door jams and window frames. These all make perfect overwintering sites, and the insects stand a good chance of surviving the winter as long as they remain in these cool, protected locations.
However, home-invading insects may take their invasion a step too far. They occasionally continue to follow the heat gradient all the way into the heated spaces. This is disastrous for the insects and no bargain for the homeowner.
The high indoor temperatures cause the insects to burn through their fat reserves and eventually starve to death. The homeowners may burn through fat chasing the insects, but they can hit the refrigerator. The starving boxelder bugs, stink bugs, lady beetles, and other accidental home invaders do not go gentle into that good night. They commonly take flight to buzz-bomb astonished home occupants.
The Best Defense is a Good Offense
Homeowners can purchase or construct effective brown marmorated stink bug traps; however, this should be viewed as “Plan B.” There are no traps for boxelder bugs, lady beetles, or the leaffooted bugs. "Plan A" should be sealing openings that allow the invaders to invade in the first place.
An ounce of calking is worth a pound of bugs. Large openings created by the loss of old caulking around window frames or door jams provide easy access into homes. Such openings should be sealed using a good quality flexible caulk or insulating foam sealant for large openings.
Poorly attached home siding and rips in window screens also provide an open invitation to the bugs. The same is true of worn-out exterior door sweeps including doors leading into attached garages; they may as well have an "enter here" sign hanging on them.
Homeowners should also inspect their attic to look for unprotected vents, such as bathroom and kitchen vents, or unscreened attic vents. While in the attic, look for openings around soffits. Both lady beetles and stink bugs commonly crawl upwards when they land on outside walls; gaps created by loose-fitting soffits are gateways into home attics.
Of course, many of these preventative measures to keep home invaders out will also keep heated and air-conditioned air in. The costs in time and materials can be recovered through reduced home energy bills.
Handle with Care
Insects that find their way into a home should be dealt with carefully. Swatting or otherwise smashing these insects can cause more damage than leaving them alone since fluids inside their bodies can leave permanent stains on furniture, carpets, and walls.
Also, smashing the home invaders can release a lingering eau de bug. Stink bugs are called stink bugs for a reason. Lady beetles also have stinky blood, and boxelder bugs as well as leaffooted bugs are armed with cloying, foul-smelling defense chemicals.
There are some effective indoor stink bug traps that exploit the bug's attraction to lights. There are even instructions online showing how to construct do-it-yourself light traps. The traps can provide some relief from home invasions until entry points are found and closed.
Small numbers of home invaders can be scooped up and discarded by constructing a simple but effective "bug collector" using a plastic pint water bottle as pictured below. Large numbers of insects can be quickly dispatched by placing a small amount of soapy water in the bottom of the bug collector.
Vacuum cleaners present their own sets of risks. A "direct-fan" type of vacuum cleaner should never be used unless modified. Passing the refuse through an impeller will create a horrifying bug-blender! Fragrant misadventures can be minimized with a slight modification involving the use of a nylon ankle sock as shown in the graphic below.
Even a "fan-bypass" type (e.g., shop vacuums) with the refuse bypassing the impeller can develop a distinctive scent if used on stink bugs and lady beetles because the insects will release their defense odor in response to swirling around inside the vacuum tank. Likewise, these vacuum cleaners can be modified as shown below.