Cockchafer

You probably know the story of Max and Moritz, written by Wilhelm Busch. They hid some cockchafers in Uncle Fritz’s bed. Uncle Fritz wasn’t at all pleased. He jumped up and “beats and stomps them all to death.”

Actually, cockchafers are completely harmless. They don't bite, sting or have venom. You can handle them without worry and let them crawl all over you.

They have hard wings, three legs on each side, and antennae on their heads. Their legs are covered with tiny hooks, which help them hold on to almost anything. A cockchafer’s underside is slightly hairy. Its sides are marked in black and white. We can see an ovipositor at the end of its abdomen. We call them cockchafers because they mainly fly around in May. They grow to about 2 to 3 cm long, making them some of the largest beetles in Europe. In our area, we find the common cockchafer and the slightly smaller forest cockchafer. They have many relatives: there are about 350,000 different species of beetles on Earth, divided into 200 families. Cockchafers belong to the scarab beetle family.

Female and male cockchafers look very similar and are difficult to tell apart. However, there is one important difference between them. You have to look at their antennae. They are made up of lamellae. Female beetles have six lamellae and males have seven. Cockchafers feed almost exclusively on leaves. In May, the leaves of deciduous trees are very young and especially juicy. Cockchafers can’t get enough of them. They eat the leaves of beech, birch, fruit and oak trees. Hardly any deciduous tree is safe from them. They need a lot of energy at this time because they are about to reproduce.

Cockchafers mate in early May. During mating, the eggs inside the female cockchafer are fertilised. About two weeks later, the female burrows around 20 cm into the ground and lays 20 to 30 eggs. These eggs are yellowish and only about 3 millimetres long. After laying her eggs, the adult cockchafer dies. About six weeks later, the young hatch from the eggs. These are cockchafer larvae, known as grubs. They immediately set off in search of something to eat. They prefer to gnaw on the roots of plants they find in the soil. In winter, they burrow deeper into the ground to protect themselves from frost. They can then be found at a depth of about one metre. The following spring, the grubs continue their big feast. In doing so, they can damage plant roots. Grubs have a hard head, which lets them bore through even firm soil. They have two strong pincers for biting. Their legs are short, and their abdomen is quite thick. It is covered by thin, whitish-yellow skin. Grubs can grow up to 5 cm long, making them longer than adult beetles.

The grubs usually spend three years underground. Sometimes they complete their development after just two years, but it can also take four years. At some point, the grubs suddenly stop eating. They burrow a little deeper into the soil and form a chamber. In this “pupal cradle,” the grub becomes a pupa. It is enclosed in a skin, does not move and does not eat. Wings and organs develop beneath the pupal skin. After another five weeks, the adult cockchafer emerges. But by then, the next winter is just around the corner. So the beetle spends several more months underground.

In May of the following year, the fully grown beetle leaves its sheltered home in the ground. The adult cockchafers don’t have much time left. Their only task now is to produce offspring. So they look for leafy trees and eat, eat, eat. A female cockchafer also has to find a mate, reproduce and lay eggs. Cockchafers can easily crawl from leaf to leaf. But if they want to get from one tree to another, they fly. They have special equipment for this. Hidden beneath their brown wing cases is another pair of wings. When cockchafers are ready to fly, they first fill their body cavities with air. They then open their wing cases, which act as wings in flight. Their soft hindwings start beating rapidly, providing the necessary thrust.

All of this happens during the last 6 weeks of their short lives. The male beetles die shortly after mating, and the females die after laying their eggs.