Last Updated on
The woodlouse spider (dysdera crocata), also known as the woodlouse hunter, slater spider, sowbug killer or sowbug assassin, is a member of the spider family Dysderidae. It is a type of hunting spider that has developed an effective method for feeding on woodlice, hence the common name.
The woodlouse hunter was first recorded in Britain by Reverend Octavius Pickard-Cambridge in 1879, but it may have been introduced some years earlier.
What Do Woodlouse Spiders Look Like?
Woodlouse spiders are medium-sized, with females up to 18 millimetres long and males about half this size. They have six eyes set in three groups of two (dyads). With its disproportionately large fangs, it is one of the scariest looking British spiders you’ll come across.
Woodlouse spiders have a shiny appearance and vary in colour from pale beige to orange or dark brown. Their legs bear long, curved bristles, which help them grip their prey. The woodlouse spider has a flattened body adapted for living under bark and stones where they wait patiently, hunting for food.
What Do Woodlouse Spiders Eat?
As their numerous names might suggest, woodlouse spiders hunt woodlice. In 2003 woodlice were found to make up 97% of this spider’s diet in one study.
When it encounters woodlice, the spider pierces its prey with its large fangs and injects a fast-acting venom. It then wraps the paralysed woodlouse in silk for later consumption.
Woodlouse spiders eat woodlice of all sizes; however, they seem able to distinguish between large and small individuals. Electrophysiological recordings show that they can detect moving but not stationary woodlice.
Where Do Woodlouse Spiders Live?
The woodlouse spider is generally found in warm regions, including Australia, Africa and the Americas, where woodlice are common.
They are often found under large rocks, logs, or in holes in wood. Many Dysdera species have been found living inside buildings where woodlice are prevalent but don’t particularly like being too close to human habitation.
Some Dysdera species construct tent-like structures or a type of silken retreat under plant pots or next to partially decayed wood, while others rest beneath lower bark on trees. This suggests that woodlouse spider colouration may play a role in camouflage and protection from predators.
What Predators Do Woodlouse Spiders Have?
A woodlouse spider’s main predator is birds such as tits and nuthatches that eat the woodlice they hunt for. Parasitic wasps (Ichneumonidae) also prey on the dysdera crocata but at a much lower rate than the birds.
Why Are Woodlouse Spiders In My House?
Finding a woodlouse spider in the house is usually rare. They will have probably wandered over from outside and crawled inside by accident. However, any woodlice inside your home may attract the spider.
Are Woodlouse Spiders Poisonous?
In short, yes. But is it harmful to humans? No.
Despite its fearsome appearance, the woodlouse spider is usually timid and will only bite humans when provoked, i.e. handled.
The venom injected during a bite will kill woodlice and other spiders, but the poison will not cause fatalities in humans. At worst, it may cause slight irritation or itching on the bite site, but no major medical problems should arise. The bite has been likened to hurt less than a bee sting but more than a stinging nettle.