Written by Joe Ballenger

Dear Entomologist,

Could you please help with a bug question. I found many small bugs on my cilantro flowers which look like carpet beetles.

Should I be worried about them in my vegetable garden and or getting in the house?

Many thanks!!

Marina

As a scientist, one of my favorite things about writing this blog is getting the opportunity to watch people make their own observations about the world around them. I think the observation Marina made here was a very cool one.

The beetles in the picture are in the genus Anthrenus, although I’m not sure which species. This group of beetles is known as the carpet beetles, due to their tendency to be found in carpets feeding on shed skin cells.

If you know a little about carpet beetles, this picture might not make sense. After all, these are insects which feed mainly on animal matter. They’re pests of insect collections, live on stuff in carpets, in old wasp nests, in bird nests eating feathers, and the occasional mummified corpse. You know…animal stuff.

So what are they doing on flowers?

Carpet Beetles Outside of Carpets

Carpet beetle ecology is pretty interesting. They’re not like other corpse feeders, like flies, because they live on the stuff which sticks around for awhile. They find stuff after it’s dried out, and done decaying. Dried animal matter is pretty common, but it’s distributed pretty far apart in space. For a little beetle like this guy, it can take a long time to find something for its larvae to live on. So they need to travel.

For these guys, moving around while looking for animal debris isn’t hard. They can fly, and are pretty good at it, but this mode of transportation requires a lot of energy. The beetles are also adapted to a high-protein diet, and the females need protein for egg production.

It’s likely they feed when they find a good source of food, but it also pays to be able to eat stuff that’s common in the environment. Pollen happens to be very common, and has a high protein content. It’s the closest thing they can get to animal matter in terms of protein content, although it’s very different in terms of nutrient composition.

This is a pattern that’s pretty common among insects which live on animals. Houseflies are very important pollinators, and Ladybird beetles will live on pollen when they can’t find food.  Spiders which live on flowers will eat pollen between meals, and web-building spiders even take the opportunity to snack on pollen which makes its way into their webs.

It’s unlikely that they’ll hurt the plants by feeding on pollen, and may even act as minor pollinators because some of that pollen is going to stick to them while they’re feeding. Since the leaves have a very different nutritional content (not to mention defensive chemicals), it’s unlikely they’ll start snacking on cilantro leaves.

Whether they’ll get into the house is harder to say. Carpet beetles come into houses from outside, and beetles found in museums often have pollen in their stomachs. While it’s likely that beetles from gardens will occasionally find their way inside, it’s also likely that the beetles from the environment will find their way inside eventually as well. An old wasp nest, or insects which accumulate inside outdoor light fixtures, will also draw them in.

That being said, it might not be a bad idea to take a closer look at cut flowers you bring into your house.