The Woodlouse Spider (Dysdera crocata), is probably one of the scarier looking spider species in the UK. Not only is it a deep red colour, but its chelicerae (jaws) operate in a side-wards motion like a pair of scissors, which can appear quite menacing. In the UK there are 2 so-called 'woodlouse spiders', the other being Dysdera erythrina. Both are very similar although D. crocata is larger and has 1 - 3 dorsal spines on the fourth leg (as can be seen in the bottom photograph), and D. erythrina prefers habitats further away from human population. It can be confused with another spider Harpactea rubicunda, but the latter has more spines and smaller chelicerae.
HABITAT AND DISTRIBUTION
The woodlouse spider inhabits areas near its prey source, so turning over a stone, bark, log or debris will probably expose one. They prefer a humid habitat and can be found in gardens, parks, and even inside buildings. In the UK this species is widespread, very common in the south but less common in Scotland. Outside of the UK the woodlouse spider can be found in Asia, North Africa, Europe and North America. Other records come from Australia, South America and South Africa.
The male and female are similar in colour, usually a dark red cephalothorax and chelicerae with long orange legs and a grey-beige abdomen. The male is smaller at only 9 - 10mm compared to the female being 11 - 15mm.
DIET, BEHAVIOUR AND REPRODUCTION
The large fangs have a horizontal biting motion rather than a vertical motion like most spiders. This is due to the woodlouse spiders main prey, woodlice! Using their fangs in this way they can flip the woodlice on its side and pierce its soft underbelly. They spend their days hidden in a silken retreat, emerging at night to hunt down their prey. The bite is likened to a weak bee sting, but the venom does not cause any major issues. Again though, spiders will only bite as a last resort. My brother was actually bitten by a woodlouse spider as a child after he held it in an enclosed hand (possibly applying to much pressure). To date he is the only person I know who can claim an 'official' bite from a spider!
OTHER NOTABLE FACTS
The woodlouse spider belongs to the family Dysderidae, one of the only group of spiders to have six eyes and not eight. The woodlouse spider originally came from the Mediterranean, as did another fierce looking species the Tube Web Spider (Segestria florentina).