White Porch Spider

Details

The White Porch Spider is the common name for Cryptachaea gigantipes, a small, pale cobweb spider in the family Theridiidae (the comb-footed spiders). It is native to south-eastern Australia and has become widely established in New Zealand and some nearby regions, where it is frequently seen living under eaves and porches – hence the name.

Taxonomy & Names

• Common English names: White Porch Spider, Long-legged House Spider

• Scientific name: Cryptachaea gigantipes (Keyserling, 1890)

• Family: Theridiidae (comb-footed spiders, same family as the Redback Spider)

• Genus: Cryptachaea

Appearance

The White Porch Spider is small but easily recognised once you know what to look for:

• Body size: adults are around 6 mm in body length, with females slightly larger than males;      the long, slender legs make the spider appear larger overall;

• Colouration: the body is amber to creamy white or pale brown with scattered darker spots on the abdomen,      giving a light, mottled appearance;

• Body shape: the abdomen is rounded and the cephalothorax relatively small, with eight long, delicate legs,      typical of many house cobweb spiders;

• Web: it builds a tangled, three-dimensional cobweb under overhangs such as eaves, porches      and rock ledges, resting in the upper part of the web.

In New Zealand the species has been compared in outline to the native katipō, but it is larger, paler and much more long-legged, and its bite is far less significant medically.

Distribution & Habitat

Cryptachaea gigantipes is native to south-eastern Australia and has been recorded from:

• eastern Australian states, where it lives on rock overhangs, in caves and around buildings;

• New Zealand, where it arrived around the late 20th century and has since spread through much of the North Island      and into parts of the South Island;

• nearby islands such as Norfolk Island, occupying both natural rock faces and human structures.

Natural habitats include rock overhangs, cave entrances and sheltered crevices. In towns and suburbs the spider has adapted very successfully to:

• the underside of eaves, porches, verandas and balconies;

• garage roofs, sheds, patio ceilings and external walls;

• areas near outdoor lights, where moths and other insects gather at night.

Behaviour & Diet

The White Porch Spider is a nocturnal web-building predator:

• by day it usually hides motionless in the upper part of its web or in a corner close to the attachment point;

• after dark it becomes more active, waiting for flying insects and other small arthropods to stumble into the sticky strands;

• once prey is caught, the spider rapidly throws more silk around it, keeping a safe distance before closing in to bite and feed.

Field observations show that the White Porch Spider will take a wide range of insects and also other spiders, including species larger and more heavily built than itself. It is therefore a surprisingly capable little predator in and around houses.

Reproduction & Maternal Care

As in many theridiid spiders, females show a degree of brood care:

• egg sacs are produced within the web and wrapped in layers of silk, then suspended among the tangle of threads;

• the female often remains nearby, guarding the egg sac against parasites and predators;

• after hatching, the spiderlings stay within the mother’s web for a time, sheltering inside the “nursery” and feeding on tiny prey      caught in the surrounding strands;

• only when they have grown enough do they disperse and construct their own small cobwebs.

Bite & Medical Significance

Although related to the medically important Redback Spider, the White Porch Spider is regarded as having amuch milder bite:

• the species is shy and tends to retreat rather than confront when disturbed;

• very few confirmed bites are known; reported symptoms include local pain, redness and swelling, sometimes with mild muscle ache,      typically resolving within about a day;

• no serious systemic effects have been documented in healthy adults.

Basic first aid – washing the area and applying a cold pack if needed – is usually sufficient. People with known allergies to arthropod bites should seek medical advice if strong or unusual symptoms develop.

Ecological Role & Relationship with People

The White Porch Spider is a classic synanthropic species – one that thrives around human buildings without being a true pest:

• it helps to reduce numbers of moths, flies and other insects attracted to lights around houses;

• it also preys on other spiders and small arthropods, contributing to the balance of invertebrate communities on walls and under eaves;

• its main “impact” on people is the presence of small cobwebs and insect remains, rather than any direct harm.

For this reason, many people choose simply to brush away excess webs from doorways while leaving the spiders themselves in place, allowing them to continue their quiet work as night-time hunters on the porch.

References

Isbister, G.K., and Gray, M.R. (2003) Effects of envenoming by comb-footed spiders of the genera Steatoda and Achaearanea (family Theridiidae: Araneae) in Australia. Journal of Toxicology, 41, 809–819. [NB species included in here as Achaearanea veruculata].

Smith, H. M., Vink, C., Fitzgerald, B. M. & Sirvid, P. J. (2012). Redescription and generic placement of the spider Cryptachaea gigantipes (Keyserling, 1890) (Araneae: Theridiidae) and notes on related synanthropic species in Australasia. Zootaxa 3507: 38-56. doi:10.11646/zootaxa.3507.1.2