The term “poisonous” is not typically accurate for spiders. They are venomous, meaning they inject toxins through a bite, rather than being poisonous, which implies harm through ingestion or touch. While many people fear spiders, only a small number of species found indoors are considered medically significant to humans. Most house spiders pose little to no threat.
Common House Spiders and Their Harmless Nature
Common house spiders are generally harmless. These include the common house spider, cellar spiders, and funnel weaver spiders. Their venom is generally not harmful to people, or their fangs are too small to effectively penetrate human skin.
The common house spider creates messy, irregular webs in secluded corners. While this spider possesses neurotoxic venom, its effects on humans are typically mild, causing only minor discomfort and localized symptoms.
Cellar spiders, often called “daddy long-legs” due to their slender bodies and exceptionally long legs, are common indoor residents. Despite an urban legend about potent venom, their bites are medically insignificant, usually resulting in a mild, short-lived stinging sensation.
Funnel weaver spiders create sheet-like webs with a funnel retreat. While they can bite, their venom is not considered medically significant to humans.
Truly Dangerous Spiders Indoors
A few spider species found indoors are medically significant and can pose a genuine threat to humans. These include certain widow spiders (genus Latrodectus) and recluse spiders (genus Loxosceles). While black widows are well-known, other widow species like the brown widow also warrant attention.
Black widow spiders are identifiable by their shiny black bodies and a distinct red or orange hourglass-shaped mark on the underside of their abdomen. The female black widow’s venom is neurotoxic, meaning it affects the nervous system. A bite can cause severe muscle pain and cramping, nausea, vomiting, and sweating, though fatalities are rare, especially in healthy adults.
Brown widow spiders also possess an hourglass marking, but it is typically yellow or orange, and their bodies can range from light to dark brown. While their venom is neurotoxic, they inject a smaller amount, leading to less severe symptoms, usually localized pain, redness, and mild muscle cramps.
Brown recluse spiders are characterized by a violin-shaped marking on their back, with the “neck” of the violin pointing towards the rear of the spider. These spiders are light to medium brown and are found in the central and southern United States. Their venom is cytotoxic, meaning it can cause localized tissue damage and necrosis, potentially leading to an open sore that may take months to heal.
Identifying Dangerous Spiders
Identifying dangerous spiders involves observing key visual characteristics and understanding their typical indoor habitats. Black widow spiders often build irregular, tangled webs in secluded, undisturbed areas like woodpiles, garages, basements, or cluttered spaces.
Brown widow spiders’ egg sacs are distinctive, appearing spiky or tufted. They prefer building webs in exposed, protected sites such as empty containers, mailboxes, and outdoor furniture. Brown recluse spiders are identified by their six eyes arranged in three pairs, rather than the usual eight eyes of most spiders. They seek out dark, undisturbed indoor areas like attics, closets, basements, and inside rarely moved furniture. It is advisable to exercise caution and avoid direct contact with any spider if its identity is uncertain.
What to Do After a Spider Bite
If a spider bite is suspected, particularly from a potentially dangerous species, immediate first aid is important. Clean the bite area gently with mild soap and water. Applying a cool compress or ice pack to the bite for 15 minutes each hour can help reduce pain and swelling. Elevating the affected limb, if possible, also assists in managing swelling.
Seek medical attention if the spider was identified as a black widow or brown recluse, if symptoms worsen, or if systemic symptoms such as severe pain, abdominal cramping, difficulty breathing, or a spreading wound appear. If safely possible, capturing the spider or taking a clear photograph can assist medical professionals in accurate identification and appropriate treatment. Avoid attempting to cut the bite or apply suction, as these actions can cause further harm.