Black Snail Beetle

Silpha atrata, also known as the Black Snail Beetle, is a member of the Silphidae family. The Silphidae comprise 21 species of large (9-30mm), distinctive species, which are mostly associated with carrion. There are exceptions to this however, with both Aclypea species being herbivores, Dendroxena quadrimaculata is an arboreal predator of caterpillars, and Silpha atrata itself is a predator of snails, hence its common name.

There are a number of distinctive characteristics that separate the Silphids from other beetle families, including a head that is often much narrower than the pronotum, very robust mandibles that are often pronounced forward, generally well developed and prominent eyes, antennae with 11 segments and robust legs which often have outwardly facing spines on the tibia (not present in Necrodes) and well-developed claws.

Silpha atrata found under deadwood on UEA campus.

Silpha atrata is one of the smaller members of the Silphidae family, measuring 10-15mm in length. Individuals of this species can vary greatly from completely black to almost red in colour, and extremes of both colours along with intermediates are all common and are often found together. S. atrata is widely distributed throughout the UK, and is abundant in a range of habitats, including woodland, meadows and gardens.

Both the adults and larvae feed on pulmonate snails and earthworms. In order to capture their prey, the adults inflict the unfortunate snails with a poisonous bite which causes the snail to withdraw into its shell and fill the entrance with a thick fluid. The beetle then eats its way through the fluid, with some assistance from a secretion that helps dissolve the fluid and the snail tissue. S. atrata has a long, extendable neck which comes in very handy for this particular feeding behaviour.

S. atrata is rather odd in its behaviour as you generally expect beetles to be inconspicuous during the cold, winter months and more noticeable during the summer, however S. atrata don't follow this train of thought; they are active under logs and beneath the bark of fallen or standing deciduous trees from October, usually in very damp conditions. In January and February they can be found in large numbers, and may be seen out in the open during the first warm days of March but after April or May, they are seldom seen, probably due to their preference for dark, damp conditions.

Three individuals of S. atrata plus one Woodlouse sp.
Found in deadwood on UEA campus.

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