Ground Spiders

What are ground spiders?

Ground spiders are the family Gnaphosidae, and there are a great many of them: roughly 2,500 described species in more than 150 genera, which places the family among the half-dozen largest in the whole order. They occur on every continent except Antarctica, and in most temperate gardens they are among the commonest spiders present even though almost nobody notices them.

The reason for that invisibility is the way they live. A gnaphosid builds no capture web at all. It spends the day inside a closed cell of tough white silk under a stone, a log, a slab of loose bark or a piece of litter, and comes out after dark to run down prey on foot. Everything about the family follows from that: a low, flattened, streamlined body, plain dark colouring, no ornament and a turn of speed that is startling when you lift the stone.

Familiar members include Herpyllus, whose parson spider is one of the commonest spiders found indoors in North America; Drassodes, the big pale-grey species of European stone walls and hillsides; and Scotophaeus blackwalli, the velvety brown spider British householders call the mouse spider.

How to identify a ground spider

The spinnerets

This is the character that settles it. The front pair of spinnerets in a gnaphosid are cylindrical, blunt-ended, clearly separated and long enough to project beyond the tip of the abdomen like two little tubes, visible from above with a hand lens or in a sharp photograph. It separates a ground spider instantly from the ant-mimic sac spiders, whose front spinnerets are conical and tapered.

Eyes

Eight eyes in two rows of four. The useful detail is the back middle pair, which in most gnaphosids are not round but flattened and irregular — oval, angular or crescent-shaped — and often pale, silvery or faintly iridescent instead of black. Our guide to spider eyes explains why a night hunter ends up with reflective eyes rather than large ones.

Size, shape and colour

Body length runs from about 2 mm in the smallest Micaria and Zelotes to around 17 mm in the largest Drassodes, with most of what you meet in the 4–12 mm range. The carapace is low and oval, the abdomen soft and elongate, the legs sturdy and spined. Colours are muted: black, slate, chocolate, grey, dull red-brown, sometimes with a silky sheen. The clearest marking in the family is the parson spider's white stripe down the front of the abdomen.

How ground spiders hunt

Gnaphosids are pure pursuit hunters. They quarter the ground after dark, detecting prey by touch and vibration rather than sight, and close the last few centimetres in a rush. Small insects, springtails, other spiders and, in some genera, ants make up the diet described in our guide to what spiders eat.

The family has one trick that sets it apart, and the enlarged spinnerets are the reason. A gnaphosid facing awkward prey — an ant that can bite back, or another spider — circles it and flicks bands of exceptionally strong, gluey silk over its legs, tethering it to the ground before closing in. Callilepis takes this further and hunts ants almost exclusively, biting at the base of an antenna and retreating until the venom works.

Silk is otherwise used only for shelter: a flattened sac of dense white silk spun into a crevice or under a stone, where the spider rests by day, moults, and in cold climates overwinters as a juvenile — one of the strategies covered in where spiders go in winter. Nothing in the family spins a snare, as our overview of the spider web notes of the hunting families generally.

Habitat and where people meet them

Anywhere with cover at ground level: under stones, logs, boards, bark and paving slabs, in leaf litter, at the base of grass tussocks, in scree and desert gravel and on bare cultivated soil. The family is most diverse in warm, dry, open country, and deserts and Mediterranean scrub are full of gnaphosids.

They also wander indoors in late summer and autumn, which is when most people meet one. A parson spider running flat out across a wall at night is a common sight in North American homes, and Scotophaeus blackwalli fills the same role in Britain, as our overview of house spiders describes; in the warm southern states, Texas especially, gnaphosids are among the spiders most often swept up indoors. None can establish a population inside, so an indoor ground spider is a lost animal rather than an infestation.

Life cycle and reproduction

Males mature in late spring or summer, abandon their retreats and travel in search of females, which is why almost every ground spider found wandering in the open by day is a male. Courtship is brief and tactile.

The female lays her eggs inside a papery, thick-walled sac of white or pinkish silk, usually a flattened disc fixed to the underside of a stone or a piece of bark and slightly domed in the middle. She stays with it, often walling herself in alongside it, and defends it until the spiderlings emerge. After that the maternal care ends: the young disperse within days or after a first moult and fend for themselves from then on — they do not stay with her until maturity, as older accounts claim.

Most temperate species complete the cycle in a year or two, overwintering as part-grown juveniles in the silk cell and maturing the following season. Being small, soft-bodied and active on open ground makes them a staple food for spider-hunting wasps, centipedes, beetles, shrews, lizards and birds, the predators catalogued in what eats spiders.

Are ground spiders venomous or dangerous?

Every ground spider has venom and uses it — the old claim that their bites are "not venomous" is simply wrong — but the venom is tuned to insects, and no species in Gnaphosidae is medically significant anywhere. No antivenom exists and none appears among the most venomous spiders.

Bites do happen, more often than with most harmless families, because these spiders wander indoors at night and end up trapped against skin in bedding or clothing; the parson spider is the usual culprit in North America. The reported result is a sharp, wasp-like sting with local redness, swelling and sometimes itching, occasionally a stronger allergic reaction in sensitive people. It resolves without treatment, and there is no tissue destruction of the kind seen with a brown recluse.

Genera of the Ground Spiders (Gnaphosidae)

Genera listed for this family on Spider Identifications — linked names have their own profile:

• Amazoromus
• Amusia
• Anagrina
• Apodrassodes
• Benoitodes
• Cabanadrassus
• Callilepis
• Canariognapha
• Diaphractus
• Drassodes
• Eilica
• Eleleis
• Homoeothele
• Herpyllus
• Intruda
• Kishidaia
• Laronius
• Leptodrassex
• Macarophaeus
• Moreno
• Nopyllus
• Odontodrassus
• Prodida
• Pseudodrassus
• Sanitubius
• Sanitubius
• Setaphis
• Synaphosus
• Theuma
• Titus
• Urozelotes
• Verita
• Wydundra
• Xerophaeus
• Xizangia
• Zelominor

Ground Spiders: species profiles

4 profiles in this family, each with identification photos, size, range, web, bite information and FAQ.

SpeciesParson (Herpyllus ecclesiasticus)Identify the eastern parson spider (Herpyllus ecclesiasticus): the cravat mark, size, speed, where it lives, and how much its bite really maSpeciesScotophaeus blackwalliIdentify Scotophaeus blackwalli, the European mouse spider: velvety grey body, size, where it lives indoors, and why it is not the Australia

Genus profiles

GenusDrassodesA guide to Drassodes ground spiders: how to identify the genus, the silk cell under a stone, where they live worldwide, and how serious a biGenusHerpyllusA guide to Herpyllus ground spiders: how to identify the genus, the species you are likely to meet, where they live, and how much a Herpyllu

Ground spider or look-alike?

Corinnidae and Trachelidae are the commonest genuine confusion: similar size, similar dark colouring, same ground-running habits. Check the front spinnerets — blunt cylinders held apart in a gnaphosid, short cones in the others — and look for the flattened back middle eyes.

Yellow sac spiders share the habit of coming indoors at night and building a silk sleeping cell, but they are pale straw or greenish, climb walls and ceilings freely, and have far longer, thinner legs than any ground spider.

Brown recluse is the identification people most want ruled out. A recluse has six eyes in three pairs, uniformly pale legs with no spines and no pattern on the abdomen; a ground spider has eight eyes, spiny legs and those projecting spinnerets. Recluses also occur only in a limited part of the United States, as our page on the Sicariidae explains.

Wolf spiders are the other frequent mix-up and are easy to exclude: they have two very large forward-facing eyes that shine in torchlight, and females carry the egg sac attached to the spinnerets.

Did you know?

• Gnaphosidae is one of the half-dozen largest spider families in the world, and new species are named every year, mostly from arid regions.
• The parson spider owes its name to the pale stripe on its abdomen, which early naturalists thought resembled the white neck-cloth worn by clergymen in the eighteenth century.
• Ground spiders use their oversized spinnerets as a weapon, flicking bands of unusually strong, sticky silk over the legs of ants and rival spiders to pin them down before biting.
• The small, glossy, often iridescent Micaria are ant mimics, and run in the jerky, antenna-waving style of an ant rather than the fluid glide of the rest of the family.
• The spider British householders call the mouse spider is not a mouse spider at all but the gnaphosid Scotophaeus blackwalli, named for its velvety grey-brown coat.