When encountering a spider, a common concern is whether it might be venomous. A “venomous” spider possesses venom potent enough to cause a significant reaction or harm to a person. While spiders are numerous and widespread, the majority pose no danger to humans. This article provides practical information to help identify potentially venomous spiders and understand the appropriate responses to suspected bites.
Understanding Spider Venom
Spider venom is a complex biological mixture primarily used to subdue prey. While almost all spiders produce venom, only a very small percentage possess venom potent enough to cause a notable reaction or harm in humans.
Visual Identification Cues
Relying on a spider’s size, color, or hairiness for identification can be misleading, as these are not reliable indicators of venom potency. Instead, focus on more specific traits.
The type of web a spider constructs can offer a clue; for instance, black widows build irregular, messy “cobwebs,” while orb weavers create symmetrical, circular webs. Funnel weavers build sheet webs that lead into a distinct funnel-shaped retreat. Another characteristic is eye arrangement. Most spiders have eight eyes, but some medically significant species, like the brown recluse, uniquely have six eyes arranged in three pairs forming a semicircle. Observing specific body markings, such as an hourglass shape or a violin pattern, along with the overall body shape, can also aid in identification.
Common Medically Significant Spiders
In North America, two spider groups are commonly considered medically significant: the brown recluse and the black widow. The brown recluse spider (Loxosceles reclusa) is light to dark brown, with a body length ranging from 1/4 to 1/2 inch and a leg span of 1 1/4 to 2 inches. Its most distinct feature is a dark violin-shaped marking on its cephalothorax, with the neck of the violin pointing towards the abdomen. The brown recluse prefers dark, undisturbed areas such as attics, basements, closets, and inside wall voids, often hiding in storage boxes or woodpiles. These spiders are nocturnal hunters.
Female black widow spiders (Latrodectus species) are shiny black and have a distinctive globular body, measuring about 1/2 inch in length. They are most recognizable by a red or orange hourglass-shaped marking on the underside of their abdomen. Males are considerably smaller and often lighter in color. Black widows build webs in quiet, undisturbed, and dark locations close to the ground. Common habitats include woodpiles, rock piles, sheds, garages, and under patio furniture.
After a Suspected Bite
If a spider bite is suspected, especially from a potentially venomous species, certain steps are appropriate. Common localized signs of a venomous spider bite can include pain, redness, swelling, blistering, and changes in skin color, sometimes forming a “bullseye” pattern with a central blister. More severe, systemic reactions might involve fever, chills, nausea, vomiting, severe muscle pain or cramps, abdominal discomfort, headache, fatigue, or sweating. Black widow bites are particularly known for causing muscle spasms and significant abdominal pain.
For immediate first aid, cleaning the bite area with soap and water is recommended. Applying a cold compress or ice pack can help reduce pain and swelling, and elevating the bitten area if possible may also be beneficial. Do not attempt to suck out venom or apply a tourniquet. Medical attention is advised if symptoms worsen, if systemic reactions develop, if the bite is from a known medically significant spider, or if the identity of the spider is unknown. Signs of infection, such as spreading redness, pus, or warmth, also warrant medical consultation.