On the ventral surface of the globular abdomen is a characteristic marking that consists of 2 equilateral triangles arranged apex to apex in an hourglass configuration. The venom of the black widow is a neurotoxin. It primarily causes systemic symptoms with little local damage at the bite site and no local necrosis. The venom mediates its effects through an initial release of massive amounts of acetylcholine at neuromuscular junctions. Reuptake of the neurotransmitters appears to be blocked as well.
Young children appear to be at highest risk for a lethal bite.
The very young, the very old, and persons with cardiovascular disease are at increased risk for complications. Envenomation can occur at any age. Initially, a severe pain in local muscle groups occurs, which then spreads to regional muscle groups. Severe cramps and contraction of musculature may extend throughout the body. The abdominal pains are frequently most severe, mimicking appendicitis, colic, or food poisoning.