Baby it’s cold outside


Asian ladybeetles are one of the critters that will most likely make their way into your home this winter in preparation for winter. (Frank/Creative Commons)

Asian ladybeetles are one of the critters that will most likely make their way into your home this winter in preparation for winter. (Frank/Creative Commons)

Fall is here, and all outside life is making preparations for winter to set in. Soon you’ll take the grill inside for the season and maybe even fix those drafty windows.

You’re not alone as you make your preparations for winter; in fact, the rest of the northern hemisphere is getting ready, and some of these critters will make their way into your home, so why not get familiar with your new roommates?

Each autumn, I am reminded of the coming winter first by the Asian ladybeetles (Harmonia axyridis) that congregate in the corners of my bedroom, looking for a slightly warmer and less windy place than outside. They pile near the corners of the ceiling and enter into a hibernation-like state, slowing their metabolism down so they don’t burn up their energy before spring comes.

This year I’ve become particularly familiar with cluster flies. These are flies in the genus Pollenia that, for lack of a better word, cluster indoors and other protected areas to ride out the winter but can be seen swarming about outside on warm winter days. They look more or less like a common house fly (Musca domestica) although they are not closely related.

Both the cluster flies and Asian ladybeetles are harmless to humans, though the cluster fly walking across my hand as I type this is rather annoying. I usually just let the spiders that share our home take care of these seasonal refugees, but the hundreds of cluster flies have driven me to marauding around the house with vacuum cleaner in hand.

While you may find it somewhat improbable that so many beetles and flies could make their way into your home, it’s even more improbable considering both of these species don’t originate from this continent.

It’s unclear where exactly cluster flies came from when they landed in North America, but it’s thought that they came over in soil on a ship hundreds of years ago. It’s believed that they are parasites of common earthworms (Lumbricus terrestris), which are also not from here!

A female fly will lay eggs directly in soil. The egg hatches into a larva (fly larvae are also called maggots) and proceeds to enter and devour the worm from the inside. Eventually the larva pierces through the worm’s skin, crawls out and goes off somewhere safe to undergo metamorphosis. Happy Halloween!

But that won’t happen to you (unless you’re an earthworm, in which case you should invest in a vacuum).

Compared to cluster flies, we know a lot more about how Asian ladybeetles came to the United States from East Asia, because it was none other than the United States Department of Agriculture that released them here. As larvae, Asian ladybeetles are voracious predators of aphids and other little invertebrate pests of crops, so the USDA imported them to use them as a biological control for plant pests.

Unfortunately they are a little too voracious and eat more than just crop pests. They will eat most any invertebrate close to them in size, including other ladybeetle species. Many of our native ladybeetles (and other insects) have become less abundant with the introduction of the Asian ladybeetle.

Enjoy your winter with your new houseguests, but don’t feel bad if you have to show them the door.

Kevin Keegan is a campus correspondent for The Daily Campus. He is a Ph.D. student in the Department of Ecology and Evolutionary Biology at UConn. He studies the systematics and biogeography of moths in the deserts of North America. He can be reached via email at

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