False widow spiders (Steatoda genus) often cause public concern due to their resemblance to black widow spiders (Latrodectus species). These spiders are frequently encountered in human environments, making accurate identification important. Understanding their specific features can help alleviate undue anxiety and provide peace of mind.
Key Physical Characteristics
False widow spiders, particularly the Noble False Widow (Steatoda nobilis), exhibit distinct physical traits. Adult females typically measure between 8.5 to 14 mm in body length, while males are slightly smaller, ranging from 7 to 10 mm. Their bodies generally appear dark brown to black, often with reddish-brown legs. A notable feature is their bulbous, glossy abdomen, which is usually round in females.
The abdomen often displays pale cream-colored markings, sometimes resembling a skull or a pentagon shape. These patterns can vary significantly, sometimes appearing faded or even absent, particularly in adult females. A narrow white or lighter band typically appears around the front part of their abdomen. Male Noble False Widows tend to have clearer abdominal markings.
Distinguishing from Other Spiders
Distinguishing false widow spiders from other arachnids, especially true widow spiders, is important for accurate identification. The primary difference between false widows (Steatoda species) and true black widows (Latrodectus species) is the distinct red hourglass marking. True black widows display a prominent red or orange hourglass shape on the underside of their abdomen, a marking absent on false widows. False widows, such as Steatoda grossa, have a rounded abdomen but show cream or pale patterns on their upper surface.
Beyond the hourglass, body coloration also differs; true black widows are usually glossy jet-black, while false widows are more commonly dark brown to black. Web structures also provide clues. True widows spin irregular, sticky webs. False widows, belonging to the same family (Theridiidae), also construct irregular, tangled cobwebs. However, their webs are generally less intricate and lack the consistent, organized appearance of some other common spiders, such as orb weavers. Compared to typical house spiders, false widows often have a more robust, globular body shape and specific abdominal markings, whereas many common house spiders have more elongated bodies or different patterns.
Typical Habitats and Web Structures
False widow spiders are commonly found in dark, undisturbed locations, both indoors and outdoors. They frequently inhabit sheds, garages, and wall crevices, preferring elevated positions within rooms, such as top corners. These spiders also establish themselves in various outdoor settings, including cacti, ivy, and under rocks or wood. Their adaptability allows them to thrive in human-associated structures year-round.
The webs constructed by false widow spiders are characteristic “cobwebs” or “tangle webs.” These are typically messy, irregular, and three-dimensional, consisting of criss-crossing threads. While they lack the geometric precision of orb-weaver webs, they can become quite dense in the center if left undisturbed. Some species, like Steatoda nobilis, build a tubular retreat within a deep crack or hole, partly concealed within their web.
Understanding Their Bites
False widow spider bites are generally compared to a bee or wasp sting. Common symptoms include localized pain, redness, and swelling at the site. In some instances, individuals might experience mild systemic effects, such as a tingling sensation, dizziness, nausea, or headache. However, severe reactions are uncommon.
The symptoms, collectively known as “steatodism,” are considered a less severe form of those caused by true widow spider bites. While the venom can cause discomfort, bites typically resolve without serious medical intervention. Complications, such as secondary bacterial infections, can arise if the bite area is not kept clean. False widows are not aggressive and usually only bite if provoked or accidentally trapped against the skin.
What to Do If You Encounter One
When encountering a false widow spider, handling the situation calmly is advisable. For isolated spiders indoors, a safe removal method involves placing a glass over the spider and sliding a piece of card underneath to trap it. The spider can then be released outdoors, away from the building. Directly handling the spider should be avoided to prevent accidental bites.
Maintaining a tidy environment can help deter spiders from establishing themselves indoors. Sealing cracks and crevices in walls, especially around windows and doors, can reduce entry points. While most encounters do not necessitate professional intervention, a pest control specialist might be considered for a significant infestation or persistent presence of spiders.