Avondale (Delena cancerides)

Physical description and identification

The Avondale spider is a big, flat, long-legged huntsman spider built for one very specific job: living in the narrow gap between dead bark and the trunk underneath it. The body is compressed from top to bottom, the legs turn out sideways rather than downward, and the whole animal can slide into a crack a coin would not fit into. Out in the open on a wall it looks enormous, but it is mostly leg.

Adults

• Size: females measure about 24–32 mm in body length and males about 20–24 mm. The leg span reaches roughly 12–15 cm (5–6 in), so an adult easily covers the palm of a hand, yet the body is only a few millimetres deep.
• Colour: mottled greyish brown to fawn, with darker flecking on the carapace and a paler abdomen carrying a faint dark median band. The chelicerae (the fang bases) are often noticeably darker, sometimes near black. Against weathered bark the pattern disappears completely.
• Eyes: eight eyes in two rows of four, all of similar size, set across the front of a broad, low head. None is enlarged, which is the quickest way to separate a huntsman from a wolf spider of similar size. At night a torch beam picks up a soft green eyeshine.
• Distinctive features: the legs are laterigrade — rotated at the base so they extend out to the sides, with the joints working in a horizontal plane. The spider walks forwards, sideways and backwards with equal ease and can reverse into a crevice without turning around. Males are slimmer, longer-legged and carry swollen tips on the pedipalps.

Eggs and the egg sac

The female builds a flattened, oval, papery sac of white silk holding roughly 200 eggs, often laying it on a silk base sheet she then abandons. She does not hang it up: the sac is fixed flat against the wood inside the bark retreat, or carried beneath her body. When the spiderlings are ready she moistens and tears the sac open so they can get out.

Spiderlings

Hatchlings emerge pale and soft and darken over successive moults. What happens next is what makes this species famous: instead of scattering, the young stay in their mother's retreat, often for months and through several moults, well past the point where other huntsman young would have dispersed. Juveniles of different ages live side by side and the mother tolerates all of them. Growth happens by moulting, and shed skins pile up under the bark.

Hunting without a web

Avondale spiders build no snare of any kind — the silk they produce goes into egg sacs, moulting platforms and draglines only. They hunt on foot after dark, walking trunks, fences and walls and running down cockroaches, moths, crickets, beetles and other spiders with a short, very fast rush. Our guide to spider webs shows how differently the web-builders solve the same problem.

Where the Avondale spider lives

Delena cancerides is an Australian species, native and widespread across much of Australia and particularly common in the drier woodlands of the south and east. The common name comes from somewhere else entirely: the spider was accidentally introduced to New Zealand, most likely in Australian hardwood timber, and became established around the Auckland suburb of Avondale. That introduced population is small and localised, but it is the one most people have heard of, which is why an Australian spider carries a New Zealand name.

The habitat is precise rather than broad. The species needs dead wood with bark still attached but no longer gripping tightly — dead wattles (Acacia), native pines and other hardwoods in Australia, and eucalypt and pine logs, fence posts and weatherboards in New Zealand. It settles readily into human structures too: woodpiles, sheds, the gaps behind loose cladding and inside garages. It needs no soil, water or plant cover, only a flat, dry, defensible slot.

Are Avondale spiders venomous?

Yes, in the ordinary way that nearly every spider is venomous: Delena cancerides injects venom to paralyse cockroaches, moths and other invertebrates. It is not medically significant to people. No antivenom exists for any huntsman spider anywhere in the world because none has been needed, and no death has ever been attributed to the species. Huntsman venom contains no potent vertebrate neurotoxins of the kind found in the Australian funnel-webs, and none of the tissue-destroying enzymes that make recluse spiders dangerous.

The species has a fearsome reputation entirely out of proportion to the facts, largely because it is the spider film-makers reach for when they need a big, active, photogenic arachnid that will not hurt anyone on set.

Can Avondale spiders bite?

They can, but it takes real provocation. The reflex of a disturbed Avondale spider is to run — flat out, sideways, into the nearest crack — and only a spider that is cornered, pinned under a hand or trapped in clothing is likely to bite. Females guarding an egg sac are the most defensive you will meet.

Because the fangs are large, the bite hurts at the time. Expect sharp local pain, a small puncture, redness and some swelling that fade over a few hours to a day; occasional reports mention brief headache or nausea after a big huntsman bite, and these settle on their own. Wash the site, apply a cold pack and take a simple painkiller if needed. Seek medical advice if pain is severe or spreading, if the wound looks infected, or if there is any sign of an allergic reaction.

Ecological importance and behavior of the Avondale spider

Among roughly 1,300 described huntsman species worldwide, Delena cancerides is the standout: it is the only member of the family known to live in permanent, stable colonies. A single retreat under one slab of bark can hold anything from a handful of spiders to well over a hundred — an adult female, her offspring of several ages, and sometimes subadults from earlier broods. They rest pressed together by day, and juveniles have been observed feeding at the same prey item. Because suitable bark is scarce and takes years to form, holding a good retreat matters more than dispersing, and that scarcity is the accepted explanation for the colonies. The tolerance is strictly local: colony members recognise one another, and an adult that wanders into a neighbouring retreat is attacked and usually eaten.

Natural predators: spider-hunting wasps (Pompilidae) paralyse adults to provision their nests. Birds such as kookaburras and currawongs take them off trunks, while geckos, skinks, centipedes and small marsupials hunt them under bark. Wandering males are the most exposed.

Prey–predator dynamics: a colony inside a dead tree is a concentrated, nocturnal, web-free predator of cockroaches, crickets, moths and beetles. Because they hunt on vertical surfaces they take a different slice of the insect fauna than the wolf spiders on the ground below them.

Seasonal behaviour: adults are active year-round in mild parts of the range and sit tight under bark in cold weather. Males mature and wander in the warmer months, which is when most indoor encounters happen. Typical lifespan is about two years, with females outliving males.

Relationship with humans: harmless and useful. Drop a container over an indoor spider, slide card underneath and carry it outside. Sprays are pointless against a spider that is only passing through, and killing one removes a free cockroach control service.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The genus Delena was erected in 1837 by the French naturalist and civil servant Charles Athanase Walckenaer, who named a large share of the world's early-described spiders.
• Avondale spiders were the live spiders used in the 1990 film Arachnophobia, chosen because they are big, active on camera and harmless to handle — so the species has spent thirty years playing deadly spiders while being nothing of the kind.
• Avondale, in Auckland, put up a sculpture of the spider near its shopping centre — a suburb adopting an introduced arachnid as a mascot.
• Colony life here is not the cooperative web-sharing of a few tropical spiders. There is no shared snare and no shared brood care, only tolerance of relatives inside a scarce home — subsocial rather than truly social.

In summary, the Avondale spider is a large, flat, fast Australian huntsman that has become famous under a New Zealand name and a Hollywood reputation it does not deserve. Its real claim to fame is biological: it is the one huntsman that lives in families, and it earns its keep eating the cockroaches in your shed.