False Widow Spiders

Several spiders in the genus Steatoda are mistaken for the rather deadly Black Widow Spider. These lookalikes are often grouped together as False Black Widow Spiders (Steatoda nobi!is). While these spiders are venomous and their bites can be painful, they're no more dangerous than a wasp sting and the spiders are non- aggressive.

The False Widow Spider is not native to Britain. It is believed it was accidentally introduced over a century  ago, possibly in  crates of fruit imported from the Canary & Madeira Islands. It was generally only found in the South West but recent mild winters have seen an increase in numbers in London and Kent.

 

Identification

The False Black Widow is a relatively small spider, with a body length being 10-1Smm (female) and only 3-6mm (male). The False Black Widow has shiny glossy appearance and globular like the Black Widow, but they lack the characteristic red double triangle or 'hourglass' marking. The abdomen of the immature female has pale chevron markings on its back and a white band around the anterior. The pattern on their bodies is often described as 'skull-shaped', which probably doesn't help their negative reputation.

Typically, the False Widow Spiders spin a loose tangle of webbing (see photo on right), with a tube of silk in one corner that leads into a crevice where the spider hides in the day. This web is often at least 1.5-2m above ground level, and sometimes higher. The typical locations are around window and door frames, and eaves, but  they have been reported from a wide range of other locations including walls, downpipes and gutters, waste pipes, porches, and outbuildings. The spiders increase in numbers during warmer months, but in late summer and autumn they may become particularly noticeable as the males wander more extensively in search of a mate.

 

Public Health Risk

False widow spiders are not aggressive and will not launch an unprovoked attack on people. When bites do occur, it seems to be a result of accidental contact with a spider (such as trapped against skin). The venom of Steatoda nobi!is can cause a short-lived reaction. Usually the only symptom is pain at the site which may radiate away from the bite. It ordinarily lasts between one and 12 hours, and rarely for more than 24 hours., It has been described as similar to a wasp sting. In the UK, so­ called spider bites are unlikely to  be a reaction to the venom itself but  are more likely to  be the result of secondary infection of an initial skin lesion.

Given that Steatoda nobilis has been present in a large area of southern England for over a century, living in and around homes, the rarity of bites is an indication of the very low threat from this species. The threat is much less than that presented by wasp stings for example.

 

How to get rid of false widow spiders

If you would like to remove spiders from your home a thorough vacuum of the affected area will remove the webs and spiders. If this is not possible you could gain control by the removal of prey by ensuring no insects are available. A insecticidal spray from your local DIY store may need to be used in this case (please ensure all manufacturer's instructions are followed).

If you would like to seek further professional advice and treatment methods you can contact the British Pest Control Association (www.bpca.org.uk) who may be able to provide a list of approved pest control contractors in your area that can assist with false widow spiders.

 

Resources for your information

 

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