Wolf Spider or Nursery Web Spider? Watch What She Carries

Two large, fast, ground-hunting spiders that turn up in gardens and occasionally indoors, are regularly mistaken for each other, and are just as regularly reported as brown recluses.

If a female is carrying eggs, the identification takes one second.

The egg sac

• Wolf spider — the sac is attached to her spinnerets and dragged behind her, like a pale ball tethered to the rear of the abdomen. She hunts, runs and climbs with it attached.
• Nursery web spider — she carries the sac beneath her body, held in her jaws and palps, which forces her to walk with her front raised. When the eggs are close to hatching she builds a tent of silk in vegetation, puts the sac inside, and stands guard on the outside. That tent is what gives the family its name.

Then the wolf spider does the thing nothing else here does: the spiderlings hatch, climb onto her abdomen, and ride there in a mass for a week or more. A large spider whose back appears to be crawling is a wolf spider with young, and it is not something to be alarmed by.

The eyes

If there is no egg sac, the eyes settle it, and both arrangements are visible with a hand lens or a phone macro.

Wolf spider — three rows: four small eyes along the bottom, two very large eyes in the middle, two medium eyes on top. The two large forward-facing eyes are the giveaway, and they reflect torchlight brilliantly. Shining a torch across a lawn at night and seeing green points looking back is the classic way to discover how many wolf spiders are living there.

Nursery web spider — eight eyes in two rows of four, more evenly sized, arranged in a shallow curve. No pair stands out.

That eyeshine is diagnostic on its own. Nursery web spiders have a much weaker tapetum and do not light up.

The rest

Neither is a brown recluse

This is the practical reason to be able to tell what they are. Wolf spiders are the single most commonly misreported recluse in North America — brown, hairy, indoors, alarming, and about the right colour.

The separation is not subtle once you know where to look, and size is the fastest of them: brown recluse or wolf spider. A recluse is small, smooth, uniformly coloured and has six eyes in three pairs. A wolf spider is large, hairy, patterned and has eight eyes with two enormous ones.

Fishing spiders — the very large ones near water and in basements — are in the nursery web family and get reported the same way. They are among the largest spiders in North America by leg span and are harmless.

Behaviour, and bites

Both hunt by running rather than by web. Neither is aggressive; both prefer to run, and both are fast enough to make that convincing.

Bites happen when one is trapped against skin — in clothing, in bedding, in a glove. The result is comparable to a bee sting: local pain and swelling for a day or two, with no tissue damage.

Neither is medically significant.

In the house

Wolf spiders come indoors incidentally, chasing prey or wandering, particularly in autumn when mature males are on the move — the season described in why there are suddenly spiders everywhere. They do not establish indoors, do not build webs and generally leave.

A glass and a piece of card works. They are fast but they are not trying to reach you.