Appearance
Like black widows, the female "S. grossa" is 6-10.5 mm in length and dark colored with a round, bulbous abdomen. Typical coloration ranges from purplish brown to black, with light-colored markings. Unlike black widows, redbacks, and other "Latrodectus" species, "S. grossa" does not have a bright red hourglass pattern or any other bright markings.Like many spiders, the male is sometimes smaller but can many times be nearly as long as the females. It measures 4.1-10.0 mm in length and is thinner than the female. The two sexes are colored similarly; however, the sexually mature male almost always has lighter, more reddish-coloured legs than the female.
Distribution
"S. grossa" is a cosmopolitan species and is found in many parts of the world, including all three coasts in North America, in Australia and New Zealand, and in Europe.A related species, commonly found in North America, is "Steatoda borealis". This spider is similar to "S. grossa" in shape, but slightly smaller, and is generally found in colder climates. This spider can be identified by colored markings on the dorsal side of its abdomen rather than on the ventral side.
Habitat
As is common with other members of the family Theridiidae, "S. grossa" constructs a cobweb, 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 warn them of larger animals that could pose a danger. They are not aggressive, and most injuries to humans are due to defensive bites delivered when a spider gets unintentionally squeezed or pinched. It is possible that some bites may 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.References:
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