Firstly, don't panic! You always thought there were no killer spiders in Britain - and you're right. But there are some that do have strong enough venom to deliver a pretty painful bite - especially if your body reacts badly.
Below are 10 particularly nasty little biters, ranked in order of the discomfort they can deliver. Some are British natives, while others are regularly coming across in boxes of fruit and the like.
There's also a description of bite symptoms, thanks to the Natural History Museum in London. In each case the offending spider was delivered to the museum with a note explaining the effects of the bite.
10. Money spider
Location: Widespread through UK, preferring damp vegetation.
Workers at a sewage treatment plant complained of being bitten by large numbers of this tiny spider, resulting in localised redness and swelling.
9. Woodlouse spider
Location: Originally from southern Europe, but has managed to get just about everywhere.
"Held on to top of finger, had to be knocked off; the bite was like that of a bee sting, leaving a white spot on finger."
8. Walnut orb-weaver spider
Location: Europe, north Africa and south Asia. Hides behind bark and in cracks in woodwork during the day.
"Pain like an electric shock from finger to elbow with the arm going numb; recovered after a few hours."
7. Black lace-weaver spider
Location: Europe and North America, all year.
"The bite, on the palm of the hand, was very painful. There was a white patch on the bite area, and a fairly large area of reddening around it."
"Swelling for three days, nausea."
6. Tube web spider
Location: Originally from southern Europe, with adults out from June to November.
"A sharp and painful bite; felt like a deep injection and caused quite a shock. However, after six hours the pain subsided."
5. Wasp spider
Location: England (June to September)
Relatively new to the UK, and pretty rare. But the bite causes immediate pain that can spread to the groin.
4. Cross (or garden) spider
Location: All over Europe from June to November.
"On the arm while in bed. Felt nausea, the arm swelled badly for 3 days."
3. Mouse spider
Location: All over Europe and North America
"Bitten on left hand. Looked like large pimple with pus-head surrounded by red inflammation. Wound burst and entire hand became septic. Wife also bitten: same painful wound for 7 days."
2. Huntsman spider
Location: South-east Asia and the Caribbean. Turns up with fruit fairly regularly because it lives on plantations.
Usually mild symptoms in humans. However, one woman was bitten in the armpit and suffered a painful swelling that lasted many days, while leaving her in a state of shock.
1. False widow spider
Location: Originally the Canary Islands, but can now be found on the southern and eastern coast and in Surrey.
One particularly bad reaction to a false widow bite went a bit like this: "Burning sensation on the right side of ribs. Increased in intensity, like being scalded, stabbing pains spread first to armpit then down right arm. Also flu-like symptoms, aches, sweats, fatigue, perspiring, cold and shaky, sick and giddy (all in first 10 minutes). Face and right arm went purplish and slightly puffy. Bite mark raised with red area c. 5 or 6cm. After 1 hour, responded to Piriton but felt unwell for 3 days."