Monday, 2 March 2009

The deadly hermit

Living in an old house means that I live alongside spiders; from the delicate daddy-long-legged forms that hang in the upper corners of rooms to the scuttling species of Tegenaria that race across the floor at the end of summer. I also encounter spiders when I am out and about looking for beetles and it may be this that has increased my interest in these much-maligned creatures.

Although we lack any truly threatening species, there are a number of spiders found here that are seriously impressive, their bulky forms and large fangs sufficient to menace the casual observer. One of these is Atypus affinis – sometimes called the purse web spider – a primitive species that is closely related to the trap-door and bird-eating spiders that one often sees in television documentaries. Atypus is a scarce spider (there is just one Norfolk record) but it is widely distributed across the southern half of Britain. One reason for its scarcity may be its requirement for undisturbed grassland and heathland habitats; another may simply be that it is easily overlooked due to its largely subterranean habits.

Atypus lives a hermitic existence, cocooned for much of her life in a sealed silken tube within a burrow excavated in the soil. The silken tube can be up to 39 cm in length but is more usually 20 cm or so long, with about a third of the tube showing above ground. This ‘above ground’ portion of the tube is camouflaged with grains of sand and other debris and can easily be mistaken for a piece of old root. The spider waits within her silken tube until some insect wanders across its surface; then she strikes, her huge fangs puncturing the silk and stabbing into the victim. The fangs hold the victim in place, pinning it to the web and, once subdued, the spider disengages one of her fangs, using tiny teeth on the base of her chelicera (the basal part of the jaw to which the fang is attached) to saw through the silk, opening up a slit through which the victim can be drawn into the cocoon. Once inside, the spider takes her meal to the base of her burrow before returning to repair the slit, ready for the next unfortunate insect to wander by.

During the winter months the spider will effectively hibernate at the base of the burrow, the upper section of the web shrinking back to become even more root-like. Come spring and the top section has to be rebuilt, a process that may be carried out annually for the seven or so years of life that a fortunate Atypus may enjoy. As the great scholar of spiders, W. S. Bristow, noted ‘this is a spider of distinction’.

No comments:

Post a Comment