Multicolored asian lady beetles

2008 December 20

These are probably the single most common species of lady beetle in our area – the Multicolored Asian Lady Beetles, Harmonia axyridis[1]. The reason for the “multicolored” name is that their coloration is all over the place, ranging from lots of spots:

to hardly any spots:

In fact, they might be Orange with ten spots, or Orange with zero spots, or even black with big orange spots. Or, as far as that goes, practically any combination of these. They are all the same species, though, as they freely interbreed with each other regardless of color.

Right about now, you are probably asking, “how on earth do you tell them from any other sort of lady beetle, then?” Well, two things: first off, the pronotum (the shield-like structure that covers the head) is generally white, with four black spots that may be distinct, or may blend together to make kind of a “W”. Second, is the question of where you find them. If they are turning up in massive quantities inside your house in the fall and winter, then it is probably them, because that’s what they do. They overwinter as adults, and tend to congregate inside structures where they are protected from the worst of the winter weather. And this is what makes them kind of a big deal: they get inside, they smell bad if crushed, tend to stain fabrics with their defensive fluids, and in some cases they might even give you a bit of a nip[2].

These are pretty well-armored even for beetles, with the head sunk in well under the pronotum, giving them kind of a helmeted appearance from the front:

And, the wing covers extend down on the underside quite a bit, so if the beetle hangs on to a surface, it can pull down the wing covers to seal tightly all around, making them pretty hard to pick up:

As a final defense, they give off a foul-smelling (and presumably bad-tasting) fluid from their leg joints if harassed sufficiently. They also fly readily, they can pop open the wings and fly off in just a second or two, unlike some beetles that have to spend some time unfurling and warming up.

One might guess from the name that they are originally from Asia, and one would be perfectly correct. These didn’t get here by accident. They were intentionally imported starting in about 1916, because they eat aphids, thrips, and similar pests, and are therefore considered to be beneficial. They evidently didn’t actually get established and start spreading in North America until a population introduced to Louisiana really took off in 1988. After that, they spread like wildfire, and are now found all over North America.

Once they got established, people started realizing that there are two sides to everything. On the one hand, it is nice that they eat aphids and all that. On the other hand, they are more annoying than other lady beetles, what with the getting into people’s houses in winter. We had to go as far as vacuuming them off of the windows some winters, because otherwise there were little drifts of dead, malodorous beetles piling up on the windowsills. They also are attracted to lights, and in the evenings they would fly around orbiting all the lights in the house for the whole winter.

There’s really only one solution to keep them out of the house: make sure the house is tight, plug all holes, and try not to sweat it when they get in anyway.

[1] This is another one that I posted already, but it was one of the first few I did. The single low-res picture and the sketchy description really aren’t adequate for such a common beetle, so I thought it would be good to re-do it.

[2] This is one of the few cases on these pages where something that could bite us, actually did bite us. Specifically, one of these bit S_ on the arm, for no real obvious reason. It was more of a startlement than anything else, but still.

7 Responses
  1. BobW permalink
    December 21, 2008

    Their populations must be either cyclical or they migrate through an area in waves. We had a plague of them about 5-7 years ago–on all the windows, inside all of the lights–but for the past 3+ years they have been virtually non-existent around our house.

    I wonder if they just had a good year following 1988 in LA and were able to spread. If they have been in the US since 1916 this cycle may have happened a number of times.

    Or I may have accidentally sealed up the holes in our house.

  2. December 21, 2008

    I gather that it is pretty typical for an invading species to have a massive population explosion when they first get into an area, followed by a crash and eventual stabilization at a more sane level. What happens is, they initially have few predators or diseases in a new territory, so they breed and breed and breed for a while. Eventually, though, either something figures out that they can be eaten, or one of their diseases from the old country comes into the area. If it’s a new predator, then they eat well, breed fast, and eventually bring the invading species under control. If it’s a disease, it sweeps through the population and wipes out most of them. I expect that this is what happened to your lady beetles.

  3. December 22, 2008

    Thanks for another great post.

  4. December 23, 2008

    Great shots and great post. And thanks for the links!

  5. JohnR permalink
    December 24, 2008

    We have a modular house, so one wall in our house is the “marriage wall” – where the two halves are joined. There’s about an inch gap inside, stuffed with insulation. I once pulled some insulation out of the bottom in the winter to try to run a speaker wire, and I discovered that we seem to be the hibernation palace for I’d guess about 60 billion of these things. On peak hibernation-spot-finding days on sunny fall days, you have to be careful to keep your mouth shut when walking around in our back yard or you’ll wind up with one in your mouth.

  6. December 25, 2008

    Off topic: Merry Christmas to you and all the family! Here’s hoping you get some really unusual infestations for Christmas.


  7. May 19, 2010

    Great shots and great post. And thanks for the links!

Comments are closed.