Once abundant throughout Europe and a major pest in the periodical years of "mass flight", it had been nearly iradicated in the middle of the 20th century through extensive use of pesticides and has even been locally exterminated in many regions. However, since a change in pest control beginning in the 1980s, its numbers have started to grow again. As they don't tolerate pollution well, their presence is usually a marker of low pollution levels.
The species M. pectoralis looks similar, but its pygidium is rounded. The cockchafer should not be confused with the similar European chafer (Rhizotrogus majalis), which has a completely different life cycle, nor with the June beetles (Phyllophaga spp.), which are native to North America, nor with the summer chafer (or "European June bug", Amphimallon solstitiale), which emerges in June and has a two-year life cycle. (All of these are Scarabaeidae, have white grubs, and are turf pests.)
Adults appear at the end of April or in May and live only for about five to seven weeks. After about two weeks, the female begins laying eggs, which she buries about 10 to 20 cm deep in the earth. She may do this several times until she has laid between 60 and 80 eggs. The common cockchafer lays its eggs in fields, whereas the Forest Cockchafer stays in the vicinity of the trees. The preferred food for adults is oak leaves, but they will also feed on conifer needles.
The larvae, known as "white grubs" or "chafer grubs", hatch after some four to six weeks. They feed on plant roots, for instance potato roots. The grubs develop in the earth for some three to four years, in colder climates even five years, and grow continually to a size of about 4–5 cm, before they pupate in early autumn and develop into a cockchafer in some six weeks.
The cockchafer overwinters in the earth at depths between 20 and 100 cm. They work their way to the surface only in spring.
Because of their long development time as larvae, cockchafers appear in a cycle of every three or four years; the years vary from region to region. There is a larger cycle of some 30 years superimposed, in which they occur (or rather, used to occur) in unusually high numbers.
Both the grubs and the imagines have a voracious appetite and thus have been and sometimes continue to be a major problem in agriculture and forestry. In the pre-industrialized era, the main mechanism to control their numbers was to collect and kill the adult beetles, thereby interrupting the cycle. They were once very abundant: in 1911, more than 20 million individuals were collected in 18 km² of forest.
Collecting adults was an only moderately successful method. In the Middle Ages, pest control was rare, and people had no effective means to protect their harvest. This gave rise to events that seem bizarre from a modern perspective. In 1320, for instance, cockchafers were brought to court in Avignon and sentenced to withdraw within three days onto a specially designated area, otherwise they would be outlawed. Subsequently since they failed to comply, they were collected and killed. (Similar animal trials also occurred for many other animals in the Middle Ages.)
In some areas and times, cockchafers even served as food. A 19th century recipe from France for cockchafer soup reads: "roast 1 lb (454 g) of cockchafers without wings and legs in sizzling butter, then cook them in a chicken soup, add some veal liver and serve with chives on a toast". And a German newspaper from Fulda from the 1920s tells of students eating sugar-coated cockchafers. A cockchafer stew is referred to in W.G. Sebald's novel The Emigrants.
Only with the modernization of agriculture in the 20th century and the invention of chemical pesticides did it become possible to effectively combat the cockchafer. Combined with the transformation of many pastures into agricultural land, this has resulted in a decrease of the cockchafer to near-extinction in some areas in Europe in the 1970s. Since then, agriculture has generally reduced its use of pesticides. Because of environmental and public health concerns (pesticides may enter the food chain and thus also the human body) many chemical pesticides have been phased out in the European Union and worldwide. In recent years, the cockchafer's numbers have been increasing again, causing damage to over 1,000 km² of land all over Europe. While this may be due to the reduced use of chemicals, some scientists also argue that, since the cockchafer thrives in warm and dry soils, the current increase in abundance may be related to climate change. At present, no chemical pesticides are approved for use against cockchafers, and only biological measures are utilised for control: for instance, pathogenic fungi or nematodes that kill the grubs are applied to the soil.
The verse dates back to the times of the Thirty Years' War, in which Pomerania was pillaged and suffered heavily. Since World War II, it is associated in Germany also with the closing months of that war, when Russian troops advanced into Eastern Germany.