Many spiders in the genus ‘Steatoda’ are mistaken for black widow spiders and therefore known as ‘false black widow spiders. They are found among human populations worldwide. False black widow spiders are less harmful to humans than black widows, however, their bite can still be extremely painful. (see False Black Widow Spider Venom below). Only the female bites.
False black widow spiders have a similar shape to widow spiders. Females are larger than males and measure up to 15 millimetres while the males measure up to 10 millimetres. False black widow spiders have round, bulbous abdomens. The male's body is thinner and more elongated than the female's, however the colour pattern is similar. Not all Steatoda species resemble widows – many have distinct colouring and are significantly smaller.
Most false black widow spiders are a brownish colour with pale markings. Apart from the colour differences from the black widow spider (Latrodectus), False black widow spiders have teeth on their chelicerae (mouth parts found in arachnids, Merostomata (horseshoe crabs) and Pycnogonida (sea spiders).
False black widow spiders are usually found in walls, fences and the bark of trees. False black widow spiders are also common around dwellings and gardens as well as under rocks and wood. Originally a native of southern Europe as far east as Georgia. Adults occur from June to November.
False black widow spiders construct a cobweb of an irregular tangle of sticky silken fibres. As with other web-weaving spiders, False black widow spiders have very poor eyesight.
False black widow spiders depend mostly on vibrations reaching them through their webs to orient themselves to prey or to warn them of danger such as larger animals that could injure or kill them.
False black widow spiders are not aggressive spiders and most injuries to humans are due to defensive bites delivered when a spider is accidentally disturbed. It is possible that some bites may result when a spider mistakes a finger thrust into its web for its normal prey; ordinarily, intrusion by any large creature will cause these spiders to flee.
False black widow spiders are now increasing in numbers in the United Kingdom due to global warming.
False black widow spiders mate in the spring and the females can produce three or more egg sacs or cocoons from May through to July. Each sac can contain 200 or more cream-coloured eggs. Although the males can live for up to 18 months, they die shortly after mating. All stages of the immature and adult spiders can be found in man-made structures throughout the year, as can the adults.
The bite from the False black widow spider is not usually felt; however, within a short space of time, a local burning sensation is followed by radiating pain. Within 20 minutes, the affected part will swell and develop a weal.
If bitten on the hand, swelling will develop within 3 – 4 hours and tingling will be felt. Two small puncture wounds in the region of the swelling, surrounded by local abnormal redness of the skin with a small bluish tinge, will occur a few hours later.
Bites by the false black widow spider generally do not have any long-lasting effects. The symptoms associated with the bite of several false black widow spider species are known in the medical profession as ‘steatodism’ and have been described as a less severe form of latrodectism (the symptoms associated with a widow spider bite). The Redback Spider antivenin has been shown to be effective at treating bites from false black widow spiders, after it was mistakenly administered to a bite victim who was incorrectly believed to have been bitten by the far more dangerous Redback spider.
Frequency of bites from false black widow spiders have increased as the species spreads into the south and east of England.
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