The Violet Oil Beetle is a very conspicuous, slow-moving, and stout blister beetle (sometimes called oil beetle) which is metallic blue. It lacks the ability to fly but otherwise exhibits very interesting behaviour. It is the most poisonous animal in the wetlands!
Description
This beetle can exceed 35mm in size. The male is smaller than the female and has bent antennae which it uses to grasp the female during mating. The Violet Oil Beetle is fat with a markedly short elytron which shimmers metallic blue. Lacking a second pair of wings, it is unable to fly. Females are swollen due to the 2,000 to 10,000 eggs they carry in their body.
Distribution
This species inhabits Central and Southern Europe. In the National Park they may be found nearly everywhere except for the xeric, or extremely dry, habitats or near the flood protection dams.
Endangerment and Conservation Status
The species is listed as "least concern", e.g. not endangered in Austria. Extremely common in the Donau-Auen National Park.
Behaviour
The development of the Violet Oil Beetle is complicated and full of risks. The female lays her many eggs in a small hollow in sandy ground which she has carved out herself. Larvae are hatched from the eggs. These have three hooked claws (they are so-called triungulin larvae) which enable them to climb up plants and into blossoms to wait for passing bees. Because they also cling to the legs of any hairy insect or spider, many beetle larvae do not make it: only those who manage to attach themselves to a living bee (solitary bee) have a chance to survive. Once attached to a bee, they allow themselves to be transported to the bee's nest. There they turn into immobile, maggot-like larvae which first eat the pollen stockpiles which the bees have gathered for their own larvae, then the bee larvae themselves. Then they enter a "fake" pupal stage, only after which the genuine pupal stage follows. The grown beetles are herbivorous, as evidenced by their green droppings.
Special Characteristics
Notorious for their toxicity. Their blood contains the toxin Cantharidin. Even minute amounts injected into the bloodstream of humans are enough to cause death. Thus it is not surprising that this beetle can afford to be so conspicuous! One relative of the Violet Oil Beetle, the so-called Spanish Fly (which is really a beetle), contains a potency-enhancing substance (aphrodisiac) which has been used to ill effect on humans – resulting even in death. The infamous murders committed by the Italian Borgia family during the Renaissance were supposedly carried out using the poison of the Spanish Fly. However, it is not dangerous to pick up a beetle using your hands, but the yellowish liquid which the beetle secretes when alarmed should be washed off carefully. Violet Oil Beetles crawl quickly on hands and limbs but also fall easily to the ground. This may be harmful to the beetles, especially females carrying many eggs, so please handle these insects with care!