The stages of the oak processionary caterpillar

The butterfly: A reproductive being

The butterfly is the adult phase of the caterpillar. The butterflies are nocturnal and fly during the summer, from late June to mid-September depending on the region. The butterfly is gray with black patterns and whitish spots. These butterflies have a very short lifespan of the order of one or two days during which the male and female butterflies will reproduce. The female will then lay eggs.

Well hidden eggs

The butterfly lays its eggs between mid-July and August. From September to February or March, the insect overwinters in the form of localized eggs in the upper part of the crown on the fine branches of well-opened trees. The bridges face south. The number of eggs per clutch can vary from 30 to 300 eggs. The egg-laying plates are a few centimeters long and are called egg-laying plates. The eggs hatch around April. The caterpillars appear before the bud break of the oaks.

A recognizable caterpillar

The caterpillar has a fairly recognizable body. The head is brownish-black. The body has bluish gray sides. The caterpillar has long tufts of silvery hairs carried by orange warts. Each segment of the body has on its dorsal surface a brownish plate where the stinging hairs are found. At the end of development, the caterpillar can reach a size of 5 cm. The caterpillar goes through 6 larval stages. It is from the third that she wears stinging hairs. From the fifth, the caterpillar makes a cocoon woven with silk on the trunk or under the carpenter branches. These are so-called gregarious caterpillars, they live in colonies and move in procession to feed on oak leaves. And are especially observable in the spring. It is at this caterpillar stage that it is responsible for leaf damage and urtications.

The chrysalis: a forgotten stage between the caterpillar and the butterfly

All caterpillars turn into butterflies. The intermediate stage between the two stages is called the chrysalis. The pupae appear at the end of spring-beginning of summer and are in the form of an individual yellowish/reddish cocoon about ten cm long. The transformation (pupation) takes place directly in the silken cocoon made by the caterpillars.

A nest of stinging silk for a long time

The caterpillars feed at dusk and at night. During the day, they gather on the leaves and twigs and make a silky, very light weaving, in which they shelter and moult (go through the different larval stages). In summer, at the end of the fifth instar, the caterpillars weave a nest made of very resistant silky threads. This nest is usually located on the trunk and main branches. It serves as protection so that the caterpillars realize their transformation into a chrysalis. 30 to 40 days later, the butterflies appear. But it is more particularly in their caterpillar form that they pose a problem for us.