Ladybugs

Ladybugs, also known as ladybirds, are insects, therefore they belong to that type of animal we call cold-blooded. During the summer they live singly, coming together only in pairs for mating. Nevertheless, they seek each other's company for the winter, under stones or logs, or under loose bark, as many as fifty or more clumping together, to lie closely packed and completely immobile. Sometimes they are found in even greater numbers, on an old post or in a porch.

It used to be thought that ladybugs, which are a type of beetle, clumped in this way to conserve the heat in their bodies. That can hardly be the reason when their aggregations are found on the surface of a post, exposed to biting winds, frost and snow. Moreover, ladybugs in hot countries will aggregate in this way during periods of extreme heat, when the air is too hot for them to move about. Then, the habit of aggregating is more a matter of taking a siesta.

There is a more likely explanation. Ladybugs are red, yellow or black, or are colored with all three. These are known as warning colors because they are usually associated with animals that sting, are poisonous or are for other reasons unpalatable. An insect-eating bird taking a ladybug in its beak will quickly drop it, and thereafter will leave ladybugs alone. It is suggested therefore that a clump of ladybugs form a large patch of warning color, and this is even more unlikely to be molested than one ladybug on its own.

These insects are attracted to the spot where they gather by the odour of those already there. Possibly this odour persists until the next winter, because ladybugs often use the same spots year after year. On certain hilltops in California there are well-known spots where ladybugs hibernate. The owners of the land collect the insects. They may gather a bushel of them with ease, and sell them to the owners of citrus groves, who liberate them in spring to feed on the scale insect pests in their fruit plantations. The following autumn a fresh generation of ladybugs finds its way to the hilltops, to be in turn collected and sent to work on the citrus trees.