Steatoda

The colour can range from sandy pale brown to reddish plum to satiny black. Like most spiders, its cephalothorax is smaller than its abdomen, which is somewhat egg-shaped, and can have white or beige to orange markings. Although sometimes not or partially visible, these markings usually consists of a frontal crescent, often with a dorsal line or triangular shapes or both. Orange to reddish-marked Steatoda paykulliana can be mistaken for the redback spider).

In common with other members of the family Theridiidae, Steatoda construct a tangled web, i.e., an irregular tangle of sticky silken fibers. As with other web-weavers, these spiders have very poor eyesight and depend mostly on vibrations reaching them through their webs to orient themselves to prey or to warn them of larger animals that could injure or kill them.

• 
  The eye arrangement of spiders in the genus Steatoda
• 
  Steatoda paykulliana
• 
  Steatoda nobilis
• 
  Steatoda grossa
• 
  Steatoda castanea

As of October 2021, the World Spider Catalog accepted the following extant species:[1]

A Steatoda found in Australia.

Those commonly mistaken for widows include:

• S. borealis. A common species in North America, often mistaken for the black widow (despite being smaller and having colored markings on the dorsal side of the abdomen, rather than the ventral side).
• S. capensis, the black cobweb or false katipo spider. It originates in South Africa, and is found in Australia and New Zealand; in the latter location it is often confused with the katipō spider.
• S. grossa, often known as the cupboard spider. A dark-colored spider which resembles specimens of Latrodectus, though without the characteristic bright marks found on most widow spiders. This spider is known to occasionally prey on true widows. Bites by S. grossa have been known to produce symptoms similar to (but far less severe than) the bites of true widows. Originally from Europe, but now found worldwide.
• S. nobilis. This spider, a native of the Canary Islands, has since been introduced into the United Kingdom and across Europe. It has been claimed that it is the UK's most venomous spider,[5] and sensationalized stories about the bite of Steatoda nobilis have featured in UK newspaper articles.[6][7] Its bite is reported to be painful, but normally no worse than a wasp sting, although one case was suspected to be a heart seizure caused by an extreme reaction to the bite.[8]
• S. paykulliana, another spider which is often confused with Latrodectus. This one is generally found in the range of Latrodectus tredecimguttatus and is frequently confused with it. Has a medically significant (but not serious) bite.

Other notable and recognizable species in the genus include:

• S. bipunctata. A common house spider in Europe.
• S. triangulosa, the triangulate cobweb spider, a common household spider noted for a pattern of triangles on the dorsal side of its abdomen. Not known to bite; found worldwide.
• S. hespera, the western bud spider. This species is commonly found in the western United States and Canada, where it is an effective predator of the hobo spider. It is often confused with the black widow, despite being significantly smaller (7 to 8 mm) and having no bright-colored markings. Not known to bite humans, but has a venom which is similar to S. paykulliana (a medically significant spider of this genus).

Steatoda is known to prey on other spiders (including true black widows), crickets, ladybugs, cockroaches, and woodlice.[9]

Some members of this genus do have bites which are medically significant in humans (such as S. grossa and S. nobilis);[10] however, bites by Steatoda species generally do not have any long-lasting effects. There may be blistering at the site of the bite, and a general malaise lasting for several days. Symptoms can include moderate to severe pain increasing for the first hour (without severe sweating).[10] Some people have reported mild to moderate nausea, headache, and lethargy. The duration of all symptoms and effects can range from 1 to 60 hours.[11][12]

The symptoms associated with the bite of several Steatoda 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 antivenom has been thought to be effective at treating bites from S. grossa, after it was mistakenly administered to a S. grossa bite victim who was erroneously believed to have been bitten by the far more dangerous redback. (While the redback antivenom appears clinically active against arachnidism caused by Steatoda spiders,^{[68][100][101][102]} as these cases are often mild and the evidence of its effectiveness is limited, this treatment is not recommended.)^[90]

They are not aggressive, and most injuries to humans are due to defensive bites delivered when a spider gets unintentionally squeezed or pinched somehow. It is possible that some bites result when a spider mistakes a finger thrust into its web for its normal prey, but ordinarily intrusion by any large creature will cause these spiders to flee.

General

• Levi, H.W. (1962). The Spider Genera Steatoda and Enoplognatha in America (Araneae, Theridiidae). Psyche 69:11-36. PDF (with key to American species)

Wikimedia Commons has media related to Steatoda.

• The World Spider Catalog
• Washington State University: Steatoda Spiders