Red-striped Oil Beetle

• GeneralIt secretes cantharidin, a toxic fluid that raises blisters on contact.
• Its development is a hypermetamorphosis: the newly hatched larva, called a triungulin, climbs onto a flower and hooks itself into the hair of a solitary bee, which unwittingly carries it back to its nest, where it devours the provisions and the eggs.
• It secretes cantharidin through the joints of its legs as droplets of haemolymph, in what is known as reflex bleeding.
• Its size and slowness make it very vulnerable to being run over and trodden on along tracks and paths.
• It secretes cantharidin from its leg joints, an oily fluid — hence the name oil beetle — that raises blisters and burns on the skin. It should not be handled, although it is otherwise harmless.
• Its black colouring with red or orange bands is aposematic: a warning that it is toxic.
• It undergoes hypermetamorphosis: it passes through larval stages of entirely different appearance. The eggs hatch into triungulins, mobile larvae with three claws per leg that actively search out the nests of solitary bees and wasps.
• Inside the nest they devour the bee's eggs and larvae and then the stored pollen and honey; afterwards they change into a very different-looking larva and finally pupate.
• Its wing cases are stunted and it has no wings, so it cannot fly. Disturbed, it plays dead.

Skeleton type

Invertebrate - chitin exoskeleton (insect)

Habitat and environment

Steppe, dry grassland and tracks

Sexual maturity

The adult has vestigial wings and cannot fly: it moves about on foot and feeds on the leaves and flowers of various plants

Gestation / incubation

It shows hypermetamorphosis: triungulin larvae emerge from the buried eggs and, unlike other phoretic blister beetles, have to search actively for the ground nests of wild bees and wasps, where they feed on their eggs and larvae while passing through larval instars of very different shapes

Litter / clutch size

Thousands of eggs per female, in a hollow in the ground

Sources consulted: https://es.wikipedia.org/wiki/Berberomeloe_majalis; El Boletin de ARBA (Lopez Colon, Bahillo de la Puebla y Lopez Septiem), seguimiento de doce primaveras en la Comunidad de Madrid; Fichas naturalistas ibericas de Berberomeloe majalis; Guadarramistas; fichas naturalistas ibericas

Best time: One of the first insects to appear in early spring; it is seen walking along paths, field margins and thyme scrub, from sea level to above 3,000 m in the Sierra Nevada