Classification

Class              Arachnida

Order              Araneae

Family            Theridiidae

The False widow spiders (Steatoda spp.) form a group of species that, because of their general resemblance to the much more notorious Black widow spiders (Latrodectus spp.), can cause concern when found in Britain. In fact, these False widow spiders and the true Black widow spiders belong to the same family, the Theridiidae (comb-footed spiders).

Identification

Six species of False widow spiders occur in the UK (Steatoda nobilis, S. grossa, S. bipunctata, S. albomaculata, S. triangulosa and Asagena phalerata), all are black or brown, rotund species up to about the size of a small finger-nail (maximum body length of adult female 15 mm). An additional species, Steatoda paykulliana, is an occasional import in fruit shipments. Females have a globular shiny abdomen, while males have a smaller one with clearer markings. All species have a narrow white or lighter band around the front of the abdomen. A trait that gives the name to the family is the presence of a particularly well-developed comb of serrated bristles on female’s fourth tarsus, visible with a lens on the largest species. The webs are a tangle of criss-cross threads which may become quite dense in the centre if left undisturbed. Here are some details for the species most likely to be seen in Britain:

Noble false widow spider Steatoda nobilis         ? 8.5–14 mm;   ? 7–10 mm.      Always larger than S. bipunctata and usually larger than S. grossa. Abdomen pattern often described as “skull-shaped” but more like a pentagon, clearer in males and dimmer or sometimes absent in females. Legs uniformly red to brown.

Cupboard spider Steatoda grossa                     ? 6.5–10 mm;   ? 4–6 mm.        Females usually darker than S. nobilis and S. bipunctata, purplish-brown, evenly-coloured dark legs or with lighter stripes, pattern of two clear triangles and lateral bars (see photo) often dim or missing in the darkest specimens. Both sexes with lighter crescent on the front of the abdomen, but this is often absent too. Front legs longer that in S. nobilis and S. bipunctata.

Rabbit hutch spider Steatoda bipunctata            ? 4.5–7 mm;     ? 4–5 mm.        Distinctive appearance with median band on abdomen, clearer in male, but fainter, partial or missing in female. Dark transversal lines over the tip of the abdomen. Legs with dark stripes visible more than in any other Steatoda in Britain.

False widow spider Steatoda paykulliana           ? 8–13 mm;      ? 4.5–6 mm.     Black body and legs, with characteristic midline pattern on abdomen, with triangles or chevrons on median band. Both these and the band in front of the abdomen can be white, pale yellow, orange or red.

Photo credits: Steatoda nobilis (2) © Michelle Brown, (4) © Joaquim Alves Gaspar / Wikimedia Commons, (5) © Graham Sant; S. grossa (6) © Mark Smith, (7) © Algirdas / Wikimedia Commons; S. bipunctata (8) © M. Virtala / Wikimedia Commons, (9) © Sanja565658 / Wikimedia Commons; S. paykulliana (10) © Eitan f / Wikimedia Commons, (11) © Yaniv Kessler / Wikimedia Commons.

Distribution and habitat

Noble false widow spider Steatoda nobilis         Well established in the southern counties and spreading north. It has been introduced with bananas from the Canary Islands and Madeira. In and around houses and other buildings. Prefers elevated positions such as the top corners of rooms and conservatories, where it hunts flying insects.

Cupboard spider Steatoda grossa                     Has colonised England, Wales and Ireland; widespread in northern Europe. Usually in houses, but occasionally in sheltered spots outside and away from habitations. Prefers hidden areas near the ground under furniture, dark low corners, where it hunts for woodlice and crawling insects.

Rabbit hutch spider Steatoda bipunctata            Widespread and common in Britain and northern Europe. It lives mainly in and around sheds, pet houses and clutter in gardens, but sometimes on tree trunks. Frequent in domestic rubbish which has been dumped illegally, well away from houses.

False widow spider Steatoda paykulliana           Not so far established in Britain, but repeatedly imported with produce from the Mediterranean, especially with grapes. It hides in cracks in the ground and under stones.

Life cycle

False widow spiders are synanthropic species (= living almost exclusively in association with man) hanging upside down in small webs known as tangle webs. Adult females can live for a few years and survive for long periods without water. Adult males live for only a few months and are usually seen in summer and autumn. They cease to feed once mature, their sole purpose being to mate. The males have smaller and more clearly marked abdomens. They also have a stridulatory apparatus of file and scraper type (ridges on the rear of the carapace and teeth under the front end of the abdomen). They court females with sounds just about audible, produced by rapid vibrations of the abdomen. The females lay eggs in white, spherical egg-sacs produced at intervals. Their number depends on the food supply and are laid from spring through to autumn. The eggs hatch in 2-4 months. Local dispersal is achieved through ballooning on silk threads. Longer distance dispersal is aided by transportation of goods by road, rail and the shipping network.

Spider bites and first aid

If handled unwisely or accidentally, False widow spiders are capable of biting humans. False widow bite effects are similar to the Black widow’s, but milder and without diaphoresis (profuse sweating).The bite is always followed by regional pain, sometimes (25%) severe (greater than a bee sting), lasting between 1-12 h, rarely over 24 h. The pain can radiate from extremities (hand, foot) towards the body. Some bites (30%) produce nausea, headache, lethargy, and malaise. Most bites cause only minor effects and resolve with no medical intervention. False widow venom cannot cause necrotic ulcers. Allergic (hypersensitivity) reactions or infections are very unlikely. Very often skin and soft-tissue infections are wrongly reported by patients as ‘spider bites’ although a spider was not actually caught biting. Doctors must be aware, so that they can recognise the real cause and treat it effectively.

If bites happen, clean the bite with mild soap and water to prevent infections. You may apply a cold pack to relieve the pain and to slow the spread of venom, but don’t apply ice directly on skin! Mild analgesics (pain killers) may help relieving the pain. If you begin to experience any serious symptoms, you should seek immediate medical help.

Conservation and control

False widows are not native to Britain and thus not granted any conservation status. You can treat them as pests and remove them from your property if you wish to reduce the risk of getting bitten. However, most people are reluctant to kill spiders and prefer to live in harmony with them. False widows seem to have found an unoccupied niche in British habitats; we have no evidence that they upset the natural balance since their arrival. In houses, they are natural enemies of many unwanted insect guests. To prevent getting bitten, be careful when putting on gloves or boots that have been left unused for a while, as spiders may seek refuge and hide in those.

If you decide sharing your home with spiders is too risky, you can catch and release them in the garden. You can buy different spider catchers which will help you handle adult spiders without actually touching them, or improvise your own devices from cups and cards – anything that will avoid you getting bitten or the spiders getting crushed in the process.

To find out more:

Falsehoods about false widows put to rest:

http://www.buglife.org.uk/news-%26-events/news/falsehoods-about-false-widows-put-rest