British Wildlife of the Week

House Spider

September is spider season. It’s the time of year, as the nights begin to draw in and autumn starts to take hold, that arachnophobes in the UK fear more than any other. There you are in your living room, snuggled up on the sofa in the evening, relaxing and watching TV, when suddenly you see it – a large house spider with long, hairy limbs rapidly scurrying across the carpet in that unnervingly jerky way that so many people dread.

There are over 650 species of spider in Britain (many of which can only be told apart by a detailed examination of their genitalia) and several live in our homes. But those that we tend to call ‘house spiders’ are the brown, long-legged species of the Tegenaria and Eratigena genera. Originally cave-dwellers, these spiders probably moved in with us almost as soon as we started to build houses. After all, our homes offer warmth and support for their webs, while the other invertebrates that enter houses to take advantage of the food we store provide easy prey for these arachnids.

House spiders are among the biggest spiders in the UK. Indeed, Tegenaria parietina is, with its 12 cm leg-span, the country’s largest. The most abundant house spider, meanwhile, is Tegenaria domestica, which, as its name suggests, has become more or less reliant on our homes, garages and outbuildings.

In fact, despite the name ‘house spider’, it is in our garages and sheds that, for most of the year at least, we are far more likely to come across these species. That is because these areas tend to be cleaned less often and are home to more potential prey. Those that do dwell inside our houses spend most of their time hidden away, unobtrusively making untidy sheet-like webs behind furniture, underneath kitchen cabinets, in wall cavities, and beneath floorboards, helping you (though you may not even realise it) by removing unwanted insects.

But towards the end of August, there is a pronounced increase in the sightings of these long-legged arachnids inside our houses. Some are spotted scuttling quickly across your living room carpet; others become stuck in your bathtub. These sightings reach a peak in mid-September and then trail off rapidly towards the end of October. So what’s going on? Why do they suddenly seemingly invade our houses?

Like many things, it’s all to do with sex.

Female house spiders are larger, live significantly longer, and are more sedentary than males. Seldom seen, they may even stay in the same flat, sheet-like web complex throughout their adult life. Males, however, are more dispersive, and in late summer and early autumn, their romantic wanderings around the house in search of females means they are much more likely to be spotted by us.

For some people, this time of year is the start of an eight-legged nightmare. No matter how good they are at catching flies, mosquitoes and cockroaches, many people simply do not like spiders. But the next time you encounter one of these creatures in your house, just remember that it’s perfectly harmless and that it’s most likely a lonely, amorous male looking for love. 

In the next British Wildlife of the Week, we’ll be looking at an alien bird that, at this time of year, outweighs all of our native birds put together – the common pheasant.