Black widow

How to recognise it

These are the features that identify a black widow. Each one is described in words so the identification works without the diagram.

1. Mature females are glossy jet black with a red or orange hourglass marking on the underside of the abdomen — visible only from below, so the spider must be seen from underneath or in its web.
2. The abdomen is distinctly globular and the body is 8 to 13 mm, with a leg span around 40 mm.
3. Males and immatures look entirely different — smaller, paler, with white and reddish stripes or spots — and are not medically significant.
4. The web is a strong, irregular, three-dimensional tangle rather than a flat orb, and is notably tough compared with other spider silk.

What it leaves behind

• Coarse, irregular tangle webs close to the ground in protected spaces — under outdoor furniture, in meter boxes, in woodpiles, under decking, in garages, and in undisturbed corners.
• Round, papery, cream-coloured egg sacs about 10 mm suspended in the web.

Why an infestation persists

Black widows are not aggressive and bite defensively, usually when pressed against skin or when a web is disturbed by hand. Envenomation causes systemic effects — muscle cramping and pain rather than local tissue damage — and is treatable. Bites are rarely fatal in the United States but genuinely warrant medical evaluation, particularly for children and older adults.

Where it occurs

Across the southern, western, and central United States; several Latrodectus species are present, with the southern black widow in the Southeast and the western black widow across the West.

Where to look for it

• Meter boxes, irrigation valve boxes, and utility housings at ground level — the single most productive place to check.
• Under outdoor furniture, especially the underside of seats and table rims.
• Woodpiles, stacked bricks, and stored materials that have stood undisturbed.
• The underside of decking, the inside of a crawl space vent, and the corners of a garage or shed.
• Inside rarely used footwear and gloves left in a garage.
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When you see it, and why

Most encounters are in late summer and autumn, when females are largest and most conspicuous and when people are handling stored materials and outdoor furniture. Egg sacs appear through the warm months. Cold weather reduces activity but does not remove the spiders from protected spaces like meter boxes, which stay usable year-round.

What getting the identification wrong costs you

False widows are killed in mistake for black widows constantly, and the distinction is straightforward once you know to check: no red hourglass underneath, and often a pale crescent on the front of the abdomen instead. That matters partly because false widows are harmless and partly because they prey on widows where the ranges overlap. In the other direction, males and immature widows look entirely different — smaller, paler, striped — and are not medically significant, so a "widow" that does not match the classic description may simply be an immature one.