Insects are a celebrated part of our natural ecosystems, but when they enter our homes, it’s rarely anything to celebrate.  Each fall as cold weather closes in, there are a few usual suspects that surface at my house to cause a hubbub.  However, these exotic houseguests are rarely a serious issue, simply existing as annoying roommates that congregate around light fixtures and windows.

Home invading insects that show up en masse are not typically native species.  With the exception of our native box elder bug (Boisea trivittata), which does invade indoor spaces, most of these intruders were introduced to US from another continent.  Many times these introductions were accidental, but in some cases they were intentionally introduced by humankind.

Each year in my home, the two most populous indoor insects that we notice in winter time are the Asian ladybeetle (Harmonia axyridi) and the brown marmorated stink bug (Halyomorpha halys).  Each of these species has a different story of their introduction to our continent, but both of these Asian invaders have rapidly occupied states from coast to coast.

The brown marmorated stink bug was first detected in Pennsylvania in 2001, although it is believed to have already been established, but just not reported prior.  This species looks very similar to many of our native stink bugs, with the characteristic shield-shaped appearance.  As cool weather sets in, adult brown marmorated stink bugs often seek out human structures for overwintering.  This propensity for human-built items has contributed to their rapid spread since introduction into the US.  

The insect winds up in many homes each winter, but also occupies vehicles, campers, boats and other large, mobile human-built objects.  As a result, many unknowing human chauffeurs have aided in its conquest toward the west coast in recent decades, with 42 states now reporting this pest. 

This insect has a wide host range, feeding on everything from vegetables and tree fruits to row crops such as corn and soybeans.  The mid-Atlantic region, which is the epicenter of its introduction, has suffered heavy economic losses from this pest in recent years since it does feed on so many important human crops.  In Illinois, it is becoming a greater problem each year and is only expected to increase in the future. 

However, in our homes, this insect is no serious problem, but rather more of a nuisance with its looming presence and stinky smell when disturbed.  Thankfully, it does not cause humans any harm and doesn’t feed, reproduce or perform any other life processed during winter time.  The only reason why we see it active is because the warmth of our home confuses this insect, delaying its normal inactivity during winter.   

The Asian lady beetle has an entirely different story associated with its introduction but also has strong ties to the US agricultural system.  Surprisingly, this pest to homeowners actually assists with control of other insect pests, such as aphids and scale, which affect both agricultural crops and the home garden.  Its introduction is shrouded in mystery as many attempts to establish this pest predator were attempted, dating back to the early 20th century.  However, it wasn’t until the 1980’s that an established population arose in southern Louisiana and the rest is history.  It now occupies nearly every state in the continental US.

Like the stinkbug, this indoor pest is looking for a warm overwintering location, and while it is quite annoying, it carries little risk to human health.  They do have the ability to pinch or bite humans, which can really get your attention, but rarely causes true harm.  When disturbed they do exude a smelly substance as a defense mechanism.  Although it’s an unforgettable smell, it’s relatively harmless for most.  Some have reported allergic reactions to these beetles, likely from the smelly fluid they release, which poses the most serious human threat.

With both of these pests, the best control method is exclusion from the home by sealing up spaces around windows, doorways, and soffits.  However, that can be a challenging task since they have the uncanny ability to squeeze through the tiniest of cracks.  If they do make it inside, I found a hand-held vacuum to be the simplest method of control.  It’s relatively easy to vacuum them up and deposit them in outdoor trash.

While these unwanted guests may occupy our homes in the colder months, take solace in the fact that warmer weather will effectively evict them and give you a chance to seal up your home before next year.

Learn more about Illinois invasive species.