Spiders are not “poisonous,” which relates to toxins ingested, but rather “venomous,” meaning they inject toxins through a bite. Massachusetts hosts several species of spiders capable of delivering venom, but the risk of a seriously harmful bite is extremely low. The vast majority of spiders encountered in the state are harmless to humans. Only two species are generally considered to be of medical significance, and understanding them is key to managing fear and risk.
Medically Significant Spiders in Massachusetts
The two spiders in Massachusetts considered medically significant are the Northern Black Widow (Latrodectus variolus) and the Yellow Sac Spider (Cheiracanthium mildei or inclusum). The Northern Black Widow is identifiable by its glossy black body and a distinct red hourglass marking on the underside of its abdomen. This red hourglass is often broken or split, differentiating it from its southern cousin. This species prefers dark, undisturbed outdoor areas like woodpiles, sheds, stone walls, and hollow logs, where it builds a messy, irregular web.
The Yellow Sac Spider is pale yellow or cream-colored, typically small, with females measuring between 5 to 10 millimeters. They do not spin webs for catching prey but instead create small silken sacs in corners of rooms, ceilings, or protected outdoor areas. These nocturnal hunters are responsible for more indoor bites than most other species. They may bite if they become trapped against skin, such as in bedding or clothing.
The Brown Recluse spider (Loxosceles reclusa), notorious for its necrotic venom, is not native or established in Massachusetts. Reported sightings are usually misidentifications or transient specimens transported from other regions. Therefore, the primary focus for concern remains the Northern Black Widow and the Yellow Sac Spider.
Common Spiders Often Mistaken as Dangerous
Many large or fast-moving spiders in Massachusetts are mistaken for dangerous species, but they pose no threat to human health. Wolf Spiders (Lycosidae family) are frequently misidentified as Brown Recluses due to their size and coloration, which ranges from dark brown to gray. These ground-dwelling hunters do not build webs to catch prey. They are often seen running across floors or outdoor areas, and their bites are not medically concerning.
The Fishing Spider (Dolomedes species) is another large spider that often lives near water but may wander into homes. They are impressive in size, with some species reaching a leg span of several inches, yet their bites are harmless. The common American House Spider (Parasteatoda tepidariorum) is often encountered indoors, weaving tangled webs in corners. Though venomous, their fangs are too small to easily penetrate human skin, and their bites cause only minimal, localized effects.
Bite Symptoms and When to Seek Medical Attention
A bite from any spider, even a harmless one, typically results in minor localized symptoms like immediate pain, redness, and slight swelling. Symptoms of a medically significant bite are distinct and depend on the venom type. A Yellow Sac Spider bite is often painful at the outset, feeling like a sharp sting, and can lead to a burning sensation with localized redness and swelling. A blister or small lesion may form, but serious long-term effects are rare.
A Northern Black Widow bite is more serious due to its neurotoxic venom, which affects the nervous system. While the initial bite may feel like only a pinprick, intense spasmodic pain begins within one to three hours and can spread through the affected limbs and body. Systemic symptoms include severe abdominal cramping, muscle rigidity, nausea, vomiting, and profuse sweating.
For any suspected spider bite, immediate first aid involves cleaning the area thoroughly with soap and water and applying a cold compress to reduce swelling. Seek medical help immediately if you suspect a Black Widow bite, especially if systemic symptoms like severe pain, muscle cramps, or nausea develop. Medical attention is also warranted for any bite showing signs of infection, such as increasing redness, warmth, pus, or if an ulcerated lesion develops and fails to heal.