By Chris Williams on September 28, 2017.

I keep reading about “invasive insects.” What does that mean exactly? In my mind they’re all invasive if they’re getting into your house. L. P., Boston, MA

You have a point but science has a different explanation. An invasive insect is one that is not native to this country but has instead been recently introduced into our country in one of several ways.

The primary method of accidental introduction is in ships’ cargo that can include stowaways hidden in imported plants, woods, foods, native crafts, or other exported goods. Invasive species can be accidentally transported on planes and they can simply migrate on their own. Sometimes insects are purposely introduced for what seems like a good reason at the time. The multicolored Asian lady beetle is an example. It was supposed to control plant-feeding insects on U.S. crops, but it quickly became a pest in its own right.


The reason you hear about invasive insects is that they almost always become problem pests, if only temporarily. The reason is that invasive insects are not usually introduced along with the predators, parasites, and diseases that keep their numbers in check in their native country. With nothing limiting them, their populations explode and they often outcompete the more desirable native insects, taking over habitats and resources and affecting other plants, animals, and sometimes the economy as a result.

The eastern U.S. hosts the largest number of pest introductions largely because of port cities. We have invasive insect problems here in the Northeast, for example, the Western conifer seed bug and the brown marmorated stink bug. While growers have to deal with damage from these plant pests, the bugs also become household pests as they move into homes to spend the winter. Forests around us have no built-in defenses against other invasive pests that attack trees such as the emerald ash borer, the hemlock woolly adelgid, and the Asian long-horned beetle.


You can often tell the insects that are invasive species by the country of origin in their name. The European paper wasp is a yellowjacket mimic that is outcompeting our native paper wasp species. The Asian tiger mosquito is becoming famous as Zika virus threatens. The aggressive Africanized honey bee got a lot of attention years ago as it moved north into the U.S. from Mexico. The Formosan termite has huge colonies and is devouring New Orleans.

While invasive species are not desirable, Mother Nature takes care of most problems in the end. Sometimes scientists visit the countries of origin to seek out predators or parasites of the invasive species and bring them back to the U.S. More often, things evolve and the invasive species eventually have predators or other population checks in this country. Sometimes, as in the case of the Africanized honey bee, the invasive species interbreeds with native species and its negative traits are diluted.

Unfortunately, as international travel and trade increase we can only expect more introductions. Our warming climate also encourages invasive species from tropical countries that are feeling right at home in the U.S.A.

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