Forestry officials from the Dojlidy Forest District wrote about the blister beetle on their website.

Why is this insect so dangerous?

Iwona Jóźwicka:

  1. The blister beetle is a species of beetle from the Meloidae family, with a dark navy-blue, blue-black or black body bearing a metallic sheen.
  2. It occurs throughout the country, but is encountered relatively rarely. It prefers grass communities in sunny areas, clearings and meadows.
  3. It is large—its body can measure up to 35 mm in length. Adult insects have shortened wing covers and a large, swollen abdomen. Females are considerably larger than males. The male’s antennae are “bent,” making it easy to distinguish the sexes.
  4. Adult insects can be found from April to June.
  5. The beetle’s name derives from the fact that, in stressful situations, the insect releases an oily yellow liquid containing a highly poisonous chemical compound—cantharidin (classified among the terpenes), one of the most powerful toxins found in nature.
  6. In the past, cantharidin was used in medicine (it stimulates the nerve endings and mucous membranes of the genitourinary system), as an aphrodisiac and to produce poison.
  7. The lethal dose for humans is approximately 0.03 g of this substance. Although a single insect cannot produce that much cantharidin, its “portion” can severely irritate human skin, especially if the substance gets into the nose or eyes.
  8. There are insects, such as the comb-horned blister beetle, that obtain the poison from dead blister beetles in order to become toxic themselves.
  9. The female blister beetle lays several thousand eggs—up to 10,000. Blister beetle larvae parasitize bees from the genera Andrena and Anthophora.
  10. The hatching larvae gather on flowers and attach themselves to bees visiting those flowers. They often attach themselves to the “wrong” insect, meaning they do not find suitable conditions for development and die.

And she adds:

Larvae attached to the bees’ legs enter their nests. There, they eat bee eggs, then molt and transform into grub-like second-stage larvae. These larvae, in turn, feed on the pollen and nectar that bees store in their nests. After molting again, a pseudopupa forms, from which the true pupa develops, followed by the adult beetle (imago). This complex developmental cycle is called hypermetamorphosis.