Tuesday, July 12, 2011

Ladybugs, good and not so good

Polished ladybug, a native one

We all love ladybugs. Some children’s books tell charming little stories about them. Even schoolchildren know that ladybugs eat bad insects. Five states, Delaware, Massachusetts, New Hampshire, Ohio and Tennessee, have chosen these handsome little beetles as their official state insects. Most ladybugs or ladybeetles deserve our esteem. They eat countless numbers of insects that damage our plants, so we are grateful.

Beetles, just like butterflies, go through a complicated life cycle. When they are growing up they look completely different from the cute little round buttons we are most familiar with. They start as larvae or, if you prefer, as grubs. Ladybug larvae are so ugly that you would want to squash them in disgust if you found them on your plants. Please, don’t! Remember that they clean up your garden from pests.

How can I describe them? They look like tiny alligators, longish, usually dark and with six stumpy little legs. They grow bigger and eventually, they curl up, become rounder, go to sleep and emerge from this stage as shiny new ladybugs. Both adults and larvae devour aphids or other little bugs with gusto.

What could be bad about ladybugs, or about some of them? It turns out that not all are worthy of our unconditional applause. Some have been brought to this country or to Europe, with the best of intentions, to fight unwanted pests. While they are quite good at this job, sometimes they wear out their welcome.

The first ladybug introduced in North America was the “vedalia” beetle. It was brought from Australia to combat the cottony cushion scale, a nasty insect that was decimating orange groves in California by sucking the plants vital juices. It was a stunning success; the beetle brought the pest under control to the great relief of citrus growers. This species of ladybeetle specializes on cottony cushion scale, which in turn specializes only on plants of the citrus family. So it never became a problem by not going beyond its boundaries. This is not the case with many other introduced insects.

Asian ladybeetle
After such success several other imported ladybugs joined the ranks of pest fighters. The most common and better know is the Asian ladybeetle or multicolored ladybug. It has spread so widely throughout North America that it is the ladybug you are most likely to see nowadays. It is not a picky eater, so its diet includes many kinds of aphids as well as other small soft bodied insects.

Infestation of Asian ladybugs in winter

And this is part of the problem; it is quite capable of eating other ladybugs or to out-compete them by its proficiency. As a result it may be driving some native ladybugs toward extinction. It also can become a nuisance to us because of its inclination to search for warm, comfortable places to spend the winter.

Convergent ladybeetle, a native one

It often finds shelter in garages, outbuildings or even our homes. Entire hordes of shelter seeking multicolored ladybeetles may invade our residences much to our annoyance. It seems that the crowds keep getting bigger each year.

Spotted ladybug, a native one

We still can’t appreciate the impact of this ladybug on some of the native species and on the ecosystems. But it doesn’t sound good. We continue to observe the development of events rather helplessly. In Europe the multicolored Asian ladybug has been declared a pest. It is too late for that here.

See:
Ladybugs
Asian ladybeetle
Good bugs gone bad
Beginners Guide to Pollinators and Other Flower Visitors

List of articles

2 comments:

David said...

I haven't seen the two-spotted ladybug that I remember from my youth...but I sure do see a lot of the Asian ones. :(

Cheri Renee said...

There are so many at my Parent's house. They are the yellow looking ones, not red. So many that they make it impossible to sit on the porch, etc. What do you think? They don't have a garden or such. There are some cows and dogs there. I would appreciate any input.