When Ladybugs Invade

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20171023A Gilles San Martin, Flickr

The Asian ladybug comes in a variety of colors, with zero to many spots. Source: Gilles San Martin, Flickr

Asian ladybugs (Harmonia axyridis), native to China, and also called Asian lady beetles or Asian ladybirds, even Halloween ladybugs (as they’re often seen in great numbers in October), have been imported into many countries as beneficial insects, the idea being to release them in huge quantities where there are aphids, their preferred prey, thus controlling the latter.

For sellers of beneficial insects, Asian ladybugs are much more interesting than native ladybugs because they naturally gather into huge groups of thousands of individuals in the fall whereas native ladybirds hibernate individually. Asian ladybugs are therefore easy to market: just harvest a few huge clumps of dormant ladybugs in the fall, store them in the refrigerator all winter, and ship the quantities requested by mail in the spring.

This worked so well that Asian ladybugs have become well established in the wild in many areas. In fact, in North America, they are now by far the most common ladybug species. They are also expanding rapidly in Europe, South America and Africa. They are no longer considered beneficial insects, but are instead being called “invasive” and “undesirable” in most countries, notably because they have all but eliminated native ladybugs, many of which are now endangered, their food source having been usurped by the invader. Also, they are often infected with a parasitic fungus that doesn’t harm them, but can kill native ladybugs. More and more countries are banning the sale of Asian ladybugs … but, in most cases, the horse is already out of the barn: they are so thoroughly established that banning their sale will have on little effect on their spread.

Fall Agglomerations

Asian ladybugs form enormous agglomerations in the fall, pressing one against the other to keep warm. Source: Steve Jurvetson, Flickr

Oddly enough, the feature that made Asian ladybugs seem so attractive originally—that of clumping together in huge masses in the autumn—has begun to be seen as a disadvantage. True enough, Asiatic ladybugs are prodigious consumers of insect pests, but when fall comes, they look for a nice, warm, protected spot in which to overwinter … and usually find it in our homes. They come indoors by the dozens, the hundreds, even the thousands, usually settling down near a bright window, attracted by the warmth they find there on a sunny day. These invasive ladybugs are even starting to destroy the wholesome image of ladybugs in general as harmless, colorful, beneficial insects that help control insect pests. Please, don’t order any more by mail, even where this practice is still allowed: there are already enough in just about any neighborhood!

If they group together so readily in the fall, it’s because they give off a pheromone that attracts their companions. And this pheromone can remain active for years, so once ladybugs have found your home to their liking, they generally come back year after year.

In addition to invading our homes, Asian ladybugs will bite if you disturb them (nothing serious, but still!), something almost no native ladybugs will do. Also, they can give off a malodorous liquid when disturbed, one that stains walls and clothing. Plus, many people have become allergic to these former friends.

Telling Ladybugs Apart

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The black W-shaped mark near the head helps identify the Asian ladybug. Source: ars.usda.gov

How to tell Asian ladybugs from native ones? That’s best done in fall, when their habit of congregating together gives them away. Otherwise, they are hard to tell from native species, especially since they can be of different colors (red, orange, yellow or black) and even the number of dots on their backs varies, from 0 to 19. One way to recognize them is that they have a W-shaped black mark near their head.

Getting Rid of Them

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You can’t beat a vacuum cleaner for quickly picking up these home invaders! Source: laidbackgardener.blog

If your home is invaded by these colorful critters, caulk all possible cracks and crevices they could get in through. If still more come indoors, find out where they are entering from and do some more caulking. As for those that are already in your home … well, it’s hard to beat a vacuum cleaner for picking them up quickly!20171023A Gilles San Martin, Flickr

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