Black Widow or Common House Spider? Look Underneath

Widows and common house spiders belong to the same family, build the same kind of web, and choose the same kind of dark, sheltered corner. That is why the two get confused so often — and why one specific check does all the work.

The hourglass, and where to look for it

Look at the underside of the abdomen.

This sounds difficult and is not, because widows hang upside down in their webs. The belly is the part facing you. Shine a torch at it from a safe distance.

• Black widow: a red hourglass on the underside. Complete in the southern and western species, split into two separate bars in the northern black widow.
• Brown widow: an orange or yellow hourglass.
• American house spider: nothing. No hourglass of any kind.
• False widow: nothing.

If there is no hourglass, it is not a widow. That is the test.

The gloss test

Once you have seen both, this works from across the room.

Widows look wet. The black is glossy, almost varnished, and it reflects light in a hard highlight.

House spiders look dusty. Dull, matte, mottled tan or grey-brown, with darker smudges across a high rounded abdomen.

Widows are a solid single colour. House spiders are patterned. That difference alone is usually enough.

The egg sac test

If there is an egg sac in the web, it may be the easiest identification of all.

• Black widow: smooth, papery, pale grey-tan, pear-shaped or round.
• Brown widow: covered in spiky silk points, like a tiny sea mine. Nothing else in North America makes an egg sac like this, and it is completely diagnostic.
• American house spider: smooth, round, tan or brownish, often several hanging in the same web.

The brown widow's spiky sac is worth memorising, because brown widows are now the commonest widow around houses in much of the deep south and southern California.

Body shape

Widow: a strikingly round, bulbous, globular abdomen on long, thin, delicate legs. The proportions look almost cartoonish.

House spider: a rounder-than-tall abdomen too, but less spherical, and the legs are proportionally shorter and stouter.

Quick reference

About the male

Male widows are small, brown, marked with pale stripes, and completely inoffensive — they are not capable of a medically significant bite. Nearly every widow anyone ever notices is a female, because the male is a fraction of her size and lives a short life.

If you have found something small, brown and striped in a widow's web, that is likely the male, and it does not change anything about how to handle the situation.

If you do have widows

They are shy. Almost every widow bite happens when the spider is pressed against skin — reaching blind into a stored box, putting on a shoe left in the garage, moving a stack of pots.

Practical measures:

• Wear gloves when moving anything that has sat undisturbed outdoors.
• Shake out shoes and gloves stored in a garage or shed.
• Check under and behind patio furniture, meter boxes, and the lips of plant pots before reaching.
• Knock down webs with a stick or a hose from a distance rather than by hand.

And it is worth knowing that cellar spiders — the long-legged ones in your ceiling corners — prey on widows. Leaving them alone is a reasonable pest control strategy.

If you are bitten

Widow venom acts systemically rather than locally, so it does not produce a rotting wound. Expect pain at the site spreading to muscle cramping, often in the abdomen and back, sometimes with sweating and nausea.

Wash the area, apply a cold pack, and seek medical care. Bring the spider only if it is already dead and to hand. Serious outcomes are uncommon and antivenom exists for severe cases.