Spanish Fly

• It is the source of so-called Spanish fly, a preparation with a reputation as an aphrodisiac that is in fact a poison: cantharidin irritates the urinary tract and has caused numerous deaths from minute doses.
• Cantharidin has been used in dermatology to remove warts, applied under controlled conditions.
• Its larvae are parasitic: they seek out the nests of solitary bees and devour the provisions and the brood.
• This beetle was the source of cantharides, one of the most famous and dangerous pharmacological preparations in history, used for centuries as a blistering agent and as a supposed aphrodisiac.
• The active compound is cantharidin, which raises blisters on contact and, if swallowed, severely damages the kidneys and the digestive tract. The lethal dose for a person is barely a few tens of milligrams.
• Its reputation as an aphrodisiac comes from a real and dangerous side effect: it irritates the urinary tract and can cause priapism, a use that has led to documented fatal poisonings.
• It undergoes hypermetamorphosis, like the oil beetle: from the eggs emerge mobile triungulins that seek out the nests of solitary bees, where they devour the eggs and provisions before turning into sedentary larvae.
• Males gift cantharidin to females during mating, and the females incorporate it into their eggs to protect them.
• Its smell is strong and unpleasant, and its aggregations can be detected from a distance.

Skeleton type

Invertebrate - chitin exoskeleton (insect)

Habitat and environment

Ash, lilac and olive trees across southern and central Europe and western Asia; the adults gather in great numbers on the leaves of the host trees

Sexual maturity

Cantharidin is synthesised by the male, who transfers it to the female during copulation; the larval hosts are solitary bees of the genera Anthophora and Colletes, and also grasshoppers and crickets

Gestation / incubation

It shows hypermetamorphosis: the first-instar larva, called a triungulin, is mobile and climbs onto a flower to wait for a solitary bee; it latches on with the three claws on each leg and lets itself be carried to the nest, where it devours the bee larva and its provisions. The following instars are sedentary and legless

Litter / clutch size

The female lays the fertilised eggs in the ground, near the entrance to the nest of a solitary mining bee; in blister beetles the clutches run to thousands of eggs

Sources consulted: https://es.wikipedia.org/wiki/Lytta_vesicatoria; Ficha de especie de Lytta vesicatoria; fichas de biologia de Meloidae; ScienceDirect (Hughes 1989); Science Advances, How colonial animals evolve; Wikipedia, Zooid; Museo Nacional de Ciencias Naturales (CSIC), ficha de Meloidae; Fichas naturalistas ibericas de Lytta vesicatoria; fichas naturalistas ibericas; La Abeja Reina, ficha de Meloidae

Best time: May and June, on ash, lilac and privet