Arizona Black Hole Spider (Kukulcania arizonica)

Physical description and identification

Kukulcania arizonica is a southwestern member of the crevice weaver family, Filistatidae, and a smaller, darker desert counterpart of the familiar southern house spider. The common name comes from the web rather than the spider: a pale silk fan on a rock face or wall with a black opening at its centre, which is where the occupant sits.

Adults

• Size: females measure about 13 mm (0.5 in) in the body and males about 6 mm. As in the rest of the genus, the male's legs are proportionally much longer, so he looks larger than his body length suggests.
• Colour: black to very dark brown, covered in a fine short pile that gives a matt, velvety finish rather than a shine. Males are often a shade lighter and browner than females.
• Eyes: all eight are crowded together on a small raised tubercle at the front of the head, reading as a single dark spot. This is the family's signature and the quickest way to rule out a recluse.
• Distinctive features: females are stocky, with short thick legs and a rounded abdomen; males are slender with long legs and forward-projecting pedipalps tipped by swollen bulbs. Both sexes carry a cribellum in front of the spinnerets and a calamistrum, a comb of bristles on the fourth legs, which together produce dry hackled silk.

Eggs

The female wraps her eggs in a loose ball of white silk and keeps it deep inside the tube at the back of the crevice, guarding it there rather than hanging it in the open web. She produces several sacs over her adult life.

Spiderlings

Hatchlings are pale and darken with each molt. They stay in the mother's web for a period, tolerating one another rather than dispersing at once, then leave on foot to find crevices of their own — frequently on the same rock face or wall, which is why occupied sites cluster.

The web

The structure is a silk-lined tube inside a crack, hole or void, with a fan of lines radiating out over the surrounding surface. One correction is worth making here, because it is repeated in most short accounts of this species: the silk is not adhesive. It is cribellate — dry, woolly, glue-free — and it holds insects by snagging their claws and bristles in a mat of extremely fine fibres. The effect on a trapped beetle is much the same as glue, but the mechanism is friction, and it is the older of the two systems spiders use. For the comparison see our guide to spider webs.

Where the Arizona black hole spider lives

The species is a Southwest and Sonoran Desert spider. It is recorded from Arizona, New Mexico, Nevada, southern Utah and the desert edge of California, and continues south into northern Mexico. It is a warm-desert animal, absent from the cold high country and the humid Southeast, where its larger relative takes over.

Habitat is defined by the cavity, not the vegetation. Natural sites are cracks in boulders and canyon walls, gaps under rock slabs, holes in dead saguaro ribs and hollows in desert timber; around people it uses adobe, block walls, stucco, mortar joints, the gaps behind fittings and the dark corners of outbuildings, porches and garden walls. Older accounts describing it as living in caves are only half right: it does use rock voids, but it is a crevice spider of exposed surfaces rather than a cave dweller, and it does far better on the sunlit outside of a desert building than in a true cave.

Are Arizona black hole spiders venomous?

Yes, in the same everyday sense as almost every spider: it has venom glands and uses them on insects. It is not venomous in any way that concerns people. No medically significant effect has been documented for this species or for any other member of the genus, no antivenom exists because none has been needed, and there is no evidence of necrosis or systemic illness. Despite the ominous name and the black colouring, it belongs nowhere near the desert recluse or the Arizona brown spider in medical terms.

Can Arizona black hole spiders bite?

They can, and it is rare. The female's whole defensive repertoire is to reverse into her tube, and males run. Bites occur when a spider is pressed against skin — a hand into a gap in a block wall, or a wandering male caught inside clothing or bedding — and the reported result is a brief pinch with a small red mark that fades within a day or two. Wash the site, apply a cold pack, and keep the spider or a clear photograph if identification is in doubt. A wound that spreads, ulcerates or comes with fever needs a doctor, but those signs point to bacterial infection rather than to this spider.

Ecological importance and behavior of the Arizona black hole spider

This is a nocturnal sit-and-wait predator with an extreme attachment to one site. By day the spider rests deep in the tube; after dark it moves to the entrance and rests its front legs on the radiating lines. Vibration, not sight, tells it that a beetle, cockroach, cricket, moth or ant has crossed the silk, and it rushes out, bites, and drags the prey back inside. The clustered eyes give poor resolution and play little part in hunting.

Natural predators: birds and desert lizards take exposed spiders, mud-dauber and other parasitoid wasps paralyse them to stock their nests, and centipedes, scorpions and larger spiders hunt them near their retreats. Wandering males are by far the most exposed stage.

Prey-predator dynamics: in an arid ecosystem where insects concentrate around structures, walls and lit doorways, a scatter of these retreats is a permanent, low-cost check on cockroaches, beetles and crickets, and the spiders themselves feed a range of desert predators.

Longevity and season: like other Kukulcania, females are long-lived by spider standards — several years in the same crevice, continuing to molt and lay — while males mature, stop feeding and leave to search, dying within weeks or months. The webs are therefore permanent fixtures while wandering spiders are strongly seasonal, appearing mainly in the warm months and after summer rains.

Relationship with humans: harmless and useful. Where a silk fan is unwanted, brushing it away and sealing the crack behind it is far more effective than spraying, because the cavity is the resource the spider is defending.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The species was described in 1935 by the American arachnologists Ralph Vary Chamberlin and Wilton Ivie, a partnership that named a large share of the spider fauna of the western United States.
• The genus name honours Kukulkan, the feathered-serpent deity of the Maya; the genus was erected by the Finnish arachnologist Pekka T. Lehtinen in 1967.
• The "black hole" of the name is the retreat entrance, not the spider. A well-established web shows a pale grey fan with an abrupt dark opening at its centre.
• Cribellate silk works without glue, which is a real advantage in a desert: a glue-coated thread dries out and loses its grip in low humidity, while a combed nanofibre band keeps working.
• Because females are so sedentary, a single crack in a garden wall can house the same individual, growing and laying, for several years running.

In summary, the Arizona black hole spider is a small, velvet-black desert crevice weaver with a dramatic name and an undramatic life. It is venomous to insects and harmless to people, its web snags prey with dry combed silk rather than glue, and once you learn the eight-eyes-on-one-bump rule you will never again mistake it for a recluse.