The arachnids, which can grow up to 12cm long, have probably been lurking all year, but emerge from their hiding places only at the end of summer.
The spiders are driven into the open by their urge to mate, having spent much of the rest of the year hidden away.
Steve McGrail, from Pro-Kill Environmental, said male spiders are reclusive, until the mating season.
He said: “The male spiders come out the woodwork during this time of year as it is breeding season and they are searching for female spiders.
“They are actually there in the home at other times of year but they are hidden away – under the floor, in the attic, in the basement. If you find them, it’s pretty much impossible to rid your house of them.
“They may disappear for a period of time, but other spiders will come in their place. The best thing to do if you find them is put them in a shed – it’s a case of out of sight, out of mind. If you put them outside they are likely to die.”