Spiders are a less than welcome seasonal sight for many. But, along with apples, conkers and reddening leaves, autumn brings out Britain's arachnids in huge numbers.

The bad news, for those who don't like them, is that this year there are more than ever. A warm spring followed by a wet summer means the eight-legged blighters are everywhere, spinning webs in the garden, getting stuck in the bath and tottering across bedroom ceilings.

That's just the male spiders, which can be seen running around as colder temperatures send them indoors to seek shelter. The females are inside already but stay fairly still and generally out of sight on skirting boards, so the bad news for arachnophobics is that there are even more of them around than it first appears.

"What's happened is that the warm spring brought an influx of pollen, so that encourages an influx of insects and crane flies and all the rest of the feeding chain. So it's more food for spiders and more of the babies from last year survive," said Angela Hale, a spider expert at Drusillas Animal Park in Alfriston, East Sussex. Along with zoos in Bristol and London, Drusillas is being inundated with calls about its courses on tackling spider phobias, and reports of strange spiders in gardens and homes.

"People suddenly start seeing big spiders everywhere and think they have some exotic breed on their hands. But the reality is that at this time of year they are mating and are pregnant. So you are seeing the males scuttling around looking for the females and then you have the females with great bulbous bodies full of eggs. But they are not a strange foreign spider, they are just pregnant and that makes their bodies not only swollen but also clumsy, so they tend to be again more visible."

Hale, who is secretary of the British Tarantula Society and keeps between 150 and 200 pet spiders, says they are essential to the ecosystem. "If we didn't have spiders we'd be inundated with all the flies and others things they eat for us. And then there are the birds, like the wren, which feed on spiders. This year's abundance of spiders will all work out in the end."

Arachnophobia is one of the most common phobias in the UK, but also the most irrational as no native British spider is capable of causing serious harm. While all spiders carry poison, most British species have jaws too weak to pierce human skin and those that are able to bite do so rarely and usually painlessly.

The latest research, from the University of Queensland, now suggests that even in Australia, where spiders can be deadly, people aren't born afraid, but learn their fear from others.

Spiders typically like dark, unswept, dusty corners, and will often stay under floorboards. Contrary to popular myth, they are not especially fond of baths, but just can't get out once they are in.

Britain is home to some 650 species but only one is harmful to humans, the noble false widow, which can deliver a nasty nip.

According to Alan Stubbs of Buglife, a conservation charity for invertebrates, people should cherish the influx of spiders. "Instead of being squeamish, look at how much they do for us, eating the flies. We are possibly the most arachnophobic country in the world but we have no reason to be. I think people are scared because they run so fast, but they are harmless. My wife and I have names for the ones in our house."

Buglife recently ran a campaign called Love Spiders, which saw a host of celebrities extolling the virtues of the much maligned creatures, and Stubbs appealed to people not to kill spiders they find in their house.

"They don't do you any harm. Leave them alone and they'll catch flies and be happy just doing their own thing. If you don't like looking at them then just have a look at a web with the dew on it and wonder why we bother with the Turner prize when nature can create such a wonderful thing."

• This story was incorrectly tagged with an Insects keyword. It was amended on 19 September.