Life Trockenrasen: Oil beetle

More than 30 species of the Meloidae family are found in Central Europe. The Oil Beetle is the most common species in Germany. The beetles prefer sandy soils as their habitat. For this reason, they are found in dry grasslands, heaths, forest edges, or even in gardens.

Characteristics and Behaviour

With its shiny blackish-blue colouring, the Oil Beetle could easily be mistaken for a drop of tar. It grows up to five centimetres long and has a stocky body with a large abdomen. Although it has wings, it cannot fly. Females are often larger than males. Especially in spring, the abdomen of female beetles appears ready to burst as they carry thousands of eggs. Oil beetles produce such a large number of eggs as part of a special reproductive strategy, with only one in a thousand larvae developing into a beetle. The female beetle buries her eggs in the ground, where they rest for about a year before hatching. The larvae then search for plants to climb and wait in the flowers for specific pollinators, such as Andrena or Colletes. When a bee arrives, the larvae cling to it and are transported to its nest. Once there, the larvae feed on the bee's eggs and food reserves of nectar and pollen. Fully nourished, the larvae pupate several times and spend another winter in the soil before emerging as beetles from March to May. The adult beetles live only about a month.

Caution! Toxic!

The oil beetle gets its name from its ability to secrete a yellow, toxic liquid from its leg joints. This oil-like poison is an important part of its defence mechanism against predators. The substance contains the active ingredient cantharidin. In the past, the poison was used to treat various diseases, as an aphrodisiac, and even for executions and assassinations. Just one beetle contains a lethal dose of poison for humans.

Threats

In Germany, the Oil Beetle is classified as vulnerable according to the Red List. With the disappearance of open landscapes such as dry grasslands, the number of beetles is also declining. Due to the length of their development period, even small disturbances have a significant impact on their survival.