Swift Spiders

Details

Swift Spiders are a group of small, fast moving ground spiders best known from Australia, where the familiar orange legged swift spider Nyssus coloripes is common in gardens and urban areas. They belong to the family Corinnidae and the genus Nyssus. Rather than relying on capture webs, swift spiders actively run over soil, leaf litter and tree trunks to hunt insects.

Taxonomy and Names

• Common names: Swift Spiders, Nyssus Spiders, Orange legged Swift Spider (for the best known species)

• Representative scientific name: Nyssus coloripes

• Family: Corinnidae

• Genus: Nyssus

Appearance

Swift spiders are small but robust hunters with a neat, streamlined build:

• Body size: adults are about 6–12 millimetres long, females slightly larger than males;      leg span is usually under 2 centimetres;

• Colouration: most species have dark brown to black bodies with bright orange or yellow bands      on parts of the legs and underside. The orange legged swift spider shows a striking pattern of orange and black on the legs;

• Body shape: the body is moderately slender with strong legs, especially the front legs, adapted for rapid running and pouncing;

• Eyes: eight eyes with a relatively well developed front row, giving fairly good vision for a small ground spider;

• Ant mimicry: in some species the body proportions and jerky movements resemble ants, which may help them move among ant trails with less attention.

Distribution and Habitat

Swift spiders of the genus Nyssus are found mainly in Australia and nearby regions, with records from eastern, southern and parts of western Australia, as well as some surrounding islands. Related corinnid spiders occur more widely in temperate and subtropical regions.

Typical habitats include:

• Garden beds, lawns, stone edges and leaf litter in towns and rural yards;

• Tree trunks, loose bark and fallen logs;

• Open shrubland, forest edges and roadside vegetation;

• External walls, fences, decking and steps around houses and sheds.

They prefer dry to slightly moist, open surfaces where they can run quickly, such as bare soil, sand, rocks and timber, often in sunny or lightly shaded spots.

Behaviour and Diet

Swift spiders are active ground hunters that search for prey rather than waiting in a web:

• They do not build large prey catching webs, but may spin a small silk retreat in a sheltered crack or under debris;

• During the day and at dusk they run rapidly over the ground, tree trunks or walls, using sight and touch to detect prey;

• Their diet consists mainly of small insects and other arthropods, including ants, aphids, small beetles, small flies and larval stages;

• Once a target is located, the spider quickly closes the distance, pins the prey with the front legs and delivers a bite, then drags it to a safer place to feed.

This combination of speed and active searching makes swift spiders important predators in the ground dwelling invertebrate community.

Reproduction and Life Cycle

The life history of swift spiders follows the general pattern of many small ground spiders:

• Males leave their hunting area after maturity and roam in search of receptive females;

• Courtship involves body postures and palpal tapping that help the female recognise the male as a mate rather than prey;

• After mating, the female produces one or more silk egg sacs in a sheltered retreat and may guard them for a period;

• Young spiderlings hatch and spend some time near the maternal retreat before dispersing and establishing their own hunting ranges.

Venom and Medical Significance

Although swift spiders are efficient predators for their size, they are small animals and their venom is adapted for subduing insect prey. Current information indicates that they are not regarded as medically significant for humans.

If a bite occurs, typical effects are limited to:

• Mild, short lived local pain at the bite site;

• Slight redness or small local swelling;

• Occasional stronger irritation in sensitive individuals.

Simple first aid, such as washing the site with soap and water and applying a cold pack if needed, is usually enough. People who experience unusual or severe symptoms should seek medical advice.

Ecological Role and Relationship with Humans

By hunting ants, small plant feeding insects and other tiny arthropods, swift spiders act as natural pest controllersin gardens, parks and agricultural land.

Because they do not build large webs and rarely interact directly with people, there is usually no need to remove them. Keeping gaps under doors sealed and reducing clutter near house foundations is generally sufficient to minimise the chance of spiders wandering indoors.

References

Raven, R. J. 2015. A revision of ant-mimicking spiders of the family Corinnidae (Araneae) in the Western Pacific. Zootaxa 3958(1): 1-258. doi:10.11646/zootaxa.3958.1.1

Framenau, V.W., Baehr, B.C. & Zborowski, P. 2014. A Guide to the Spiders of Australia, Reed New Holland.

Whyte, R. & Anderson, G. 2017. A Field Guide to Spiders of Australia. CSIRO Publishing.