Thin-legged Wolf (Pardosa)

Physical description and identification

Pardosa is a genus of small, agile, ground-living wolf spiders erected by the German arachnologist Carl Ludwig Koch in 1847. More than five hundred species are recognised, making it the largest genus in the family Lycosidae and one of the largest in the whole order. The date 1833 is sometimes quoted for the genus, but the accepted authority is Koch, 1847.

Adults

• Size: these are small spiders. Females generally measure about 4–9 mm in body length and males 3–7 mm, so even a large individual is shorter than a grain of rice. The long legs make them look bigger than they are.
• Colour: most species are brown, grey or blackish, marked with a pale central band down the carapace and a pair of paler side bands, and with a lighter lance-shaped mark and faint chevrons on the abdomen. Males are frequently darker and more contrasty than females, with black-tipped or conspicuously pale pedipalps.
• Eyes: eight eyes in three rows — four small ones across the face, two large forward-facing eyes above them and two set wide on top of the head. The large pair carry a reflective tapetum, so the whole genus shows eyeshine in a torch beam. See our guide to spider eyes.
• Distinctive features: the legs are the giveaway. They are thin, long and armed with strong, obvious spines, quite unlike the thick, hairy legs of the big burrowing wolf spiders. Species-level identification almost always needs an adult and a microscope, because colour patterns overlap heavily.

Eggs and egg sac

The egg sac of this genus is unusually easy to recognise. It is lens-shaped rather than spherical, seamed around the rim, and often a distinct grey-green or bluish green when newly spun, fading to grey-brown as the eggs develop. The female fastens it to her spinnerets and tows it behind her while hunting. Incubation is not a mystery, as is sometimes claimed: depending on species and temperature the young normally hatch within about two to four weeks, faster in warm weather and slower in cool.

Spiderlings

The mother opens the sac when the young are ready and they climb onto the top of her abdomen, holding on to specialised hairs. They do not feed while riding, living on stored yolk, and after roughly a week they leave. Dispersal is often aerial: Pardosa spiderlings are well known for ballooning, climbing a grass stem, raising the abdomen and releasing silk until the drag carries them away. Most temperate species then mature within a single year.

Hunting instead of a web

No Pardosa builds a capture web. They are pursuit hunters that rely on vision and speed, and — unusually for wolf spiders — many are active in bright daylight, running and basking on open ground where their body temperature can rise. Silk is spun for draglines, for a shallow retreat under a stone and for the egg sac. Courtship happens in the open too: males wave and drum their pedipalps in front of a female in a display that is species-specific and can keep similar species apart.

Where thin-legged wolf spiders live

Pardosa is genuinely cosmopolitan. Species occur throughout Europe and Asia, across North and Central America, in Africa, South America, the Caribbean and parts of Oceania, with by far the greatest diversity in the northern hemisphere. The genus reaches further north than almost any other spider: Pardosa glacialis lives on Greenland and the Canadian high Arctic islands, and several species are among the commonest animals of the tundra. It is a familiar genus everywhere from Britain to Canada.

What unites the habitats is openness. Thin-legged wolf spiders prefer sunlit ground with low or patchy cover: gravel river shores and lake margins, salt marsh, grassland and meadows, heath and bog, alpine scree, arctic tundra, ploughed fields, lawns, garden paths and woodland clearings. Some are extreme specialists of stony shorelines, sphagnum bogs or high screes, while others are among the first colonisers of disturbed ground. See where spiders live.

Are thin-legged wolf spiders venomous?

Every Pardosa is venomous in the sense that it uses venom to subdue insects, and every Pardosa is harmless to people. The venom is tuned to small arthropods, the dose is minute, and there is no antivenom for any wolf spider because none has ever been required. No species in the genus is medically significant anywhere in its worldwide range.

Size alone settles most of the question. A 5 mm spider with correspondingly small fangs can rarely break human skin at all, and claims connecting wolf spider bites to spreading skin damage are misidentifications of other causes.

Can thin-legged wolf spiders bite?

In principle yes, in practice almost never. These spiders flee from anything as large as a human hand, and their speed makes escape a far better option than defence. The rare recorded bites involve a spider held between the fingers or trapped against skin.

Where a bite does happen the result is a brief sting, perhaps a pinprick mark and a little redness, gone within hours. Wash the spot with soap and water and apply a cold pack if it is uncomfortable; nothing else is needed. As with any small break in the skin, keep an eye out for signs of infection over the following days, and seek advice if you develop hives, swelling elsewhere on the body or difficulty breathing, which would point to an allergic reaction rather than the venom.

Ecological importance and behavior of Pardosa spiders

Few spiders matter more to agriculture. Pardosa species occur at very high densities in fields, grassland and paddy, and they eat a steady flow of aphids, springtails, flies, leafhoppers, small beetles, ants and other spiders. Pardosa pseudoannulata is one of the principal natural enemies of planthoppers in Asian rice, and Pardosa milvina is among the most intensively studied spiders in North American row-crop research. As a group they are a large, unpaid component of integrated pest management.

Natural predators: spider wasps and other hunting wasps, ground beetles, birds, lizards, frogs, shrews and larger wolf spiders all take them, and parasitoid wasps and flies attack both adults and egg sacs. Several studies have shown Pardosa shifting where and when it forages once the chemical traces of a larger wolf spider are present.

Prey-predator dynamics: small, abundant and quick to colonise disturbed ground, thin-legged wolf spiders sit in the middle of the food web rather than at the top, converting huge numbers of tiny insects into food for vertebrates.

Seasonal behavior: most temperate species are annual. Juveniles overwinter in litter or soil, mature in spring or early summer, and females carry egg sacs through the warm months, often producing more than one. In the Arctic the cycle stretches out and maturation may take two years or more, which is one reason northern Pardosa populations are used to track the effects of a warming climate.

Relationship with humans: entirely positive. They do not live in houses, they do not bite in any meaningful sense, and they are among the clearest examples of free pest control in a garden or field.

Species in the genus and similar spiders

Quick facts

Did you know?

• The greenish tint of a fresh Pardosa egg sac is one of the quickest ways to recognise the genus in the field — no other common wolf spider group carries a lens-shaped sac of that colour.
• Many species are actively heliothermic: they bask to raise body temperature and can hunt at air temperatures that keep other spiders inactive, which is a large part of why the genus dominates cold climates.
• Arctic Pardosa populations have become model organisms for climate research, because their body size, brood size and timing all shift measurably as the season lengthens.
• A single hectare of grassland or arable field can hold tens of thousands of thin-legged wolf spiders.

In summary, Pardosa is the small, fast, sun-loving core of the wolf spider family: more than five hundred species, a lens-shaped green egg sac, spiny thin legs, and an ecological role out of all proportion to a body a few millimetres long.