Aphonopelma caniceps

Physical description and identification

Aphonopelma caniceps is a medium-sized member of Aphonopelma, the tarantula genus that dominates North America. It is a New World theraphosid, and that single fact explains most of its biology: heavy, slow, ground-bound, long-lived, and defended by barbed abdominal hairs rather than by a dangerous bite.

The species name is descriptive: Latin canus means grey or hoary and -ceps refers to the head, so caniceps points to the pale, frosted carapace set against a darker body — clearest when the animal is fresh from a moult.

Adults

• Size: adults span roughly 10–13 cm (4–5 in) across the legs, which is moderate for the genus — much smaller than a goliath birdeater and comparable to a Arizona blond. Body length is around 4–6 cm.
• Colour: brown to dark grey overall, with a lighter, greyish carapace and rust or copper tones in the abdominal and leg hairs. Colours are strongest immediately after a moult and fade between moults.
• Build: robust and densely hairy, with noticeably thick legs. Tarantulas of this build are walkers and diggers, not climbers.
• The bald patch: older individuals, especially females, often show a bare dark spot on top of the abdomen. This is not age or illness. It is where the spider has repeatedly kicked off its urticating hairs, and the patch fills in again at the next moult.
• Urticating hairs: the defining New World feature. The dorsal abdomen carries thousands of tiny barbed setae that the spider flicks into the air with its hind legs when threatened. They cause itching and rash and, in the eyes, a serious inflammation. Old World tarantulas such as Poecilotheria have none and bite instead.
• Sexes: mature males are slimmer and longer-legged than females, with swollen palpal bulbs and hooks on the underside of the front legs used to hold a female's fangs during mating.

Eggs and egg sacs

The female mates in late summer, stores the sperm, and builds her egg sac weeks or months later inside the burrow. She wraps the eggs in a thick silk purse and turns and guards it until the spiderlings emerge. Aphonopelma sacs commonly hold a few hundred eggs, scaling with the size of the female.

Spiderlings

Newly emerged spiderlings are pale and only faintly marked. They stay briefly in the mother's burrow, then disperse on foot and dig small burrows of their own nearby. Growth is famously slow: a female may take eight to twelve years to reach maturity, adding size at each moult. Legs lost to a predator regrow over several moults, small at first and full-sized after two or three.

The burrow

This species builds no capture web. Silk is used to line the burrow walls, to seal the entrance during winter and before a moult, to make the sheet on which the male deposits sperm, and to wrap the eggs — never as a snare. The burrow is a sloping tunnel under a rock, shrub or bank, often with a low silk collar at the mouth and silk lines around it that carry a passing insect's vibrations down to the waiting spider.

Where Aphonopelma caniceps lives

Aphonopelma caniceps is a Mexican species. That is worth stating clearly, because it is often described only as living "in North America", which readers reasonably take to mean the United States. It is not one of the twenty-nine Aphonopelma species recognised from the US in the comprehensive 2016 revision of the genus, and records place it south of the border. Its US relatives — the desert tarantula, the Texas brown and the Arizona blond among them — fill the same role in Texas, Arizona and the rest of the southwest.

The habitat is the standard Aphonopelma template: dry scrub, thorn forest, grassland and rocky desert margins, at low to moderate elevation, with soil firm enough to hold a tunnel. Burrows are placed under stones, at the base of shrubs and agaves, in road cuts and on slopes that shed rain. Spiders in such country spend the hot, dry months plugged underground and emerge when humidity and prey return.

Is Aphonopelma caniceps venomous?

Yes, in the ordinary sense that all tarantulas are venomous: the venom subdues insects. It is not medically significant to people. No Aphonopelma is, and no death or serious systemic illness has ever been attributed to the genus. There is no antivenom because none is required.

This is the key difference between the New World tarantulas and their Old World relatives. The African baboon spiders such as the king baboon, and the Asian ornamentals, have potent venom that can cause hours or days of severe cramping. Aphonopelma traded that chemical defence for a mechanical one — the urticating hairs — and the result is a spider that is unpleasant to annoy but essentially harmless to hold a conversation next to.

Can Aphonopelma caniceps bite?

It can, but it very rarely does. The escalation is predictable: the spider walks away first; if cornered it turns its abdomen towards the threat and kicks hairs; if that fails it rears into a threat posture with the front legs raised and the fangs exposed; only then does it strike. Most keepers of Aphonopelma never see the last stage.

A bite feels like a bee sting, with local pain, a little swelling and two clear puncture marks; the fangs are long enough that the mechanical puncture is often the worst part. Wash the site with soap and water, apply a cold pack, and watch for infection or an allergic reaction rather than for venom effects.

Ecological importance and behavior of Aphonopelma caniceps

This is a sit-and-wait predator with an exceptionally small home range. An adult female may spend her whole life within a few metres of one burrow, sitting at the entrance after dark and retreating underground at the slightest disturbance.

Diet: crickets, beetles, grasshoppers, roaches, moths, centipedes, scorpions and other spiders, with the occasional small lizard for a large female. Reports that tarantulas of this size regularly eat small mammals are not supported; that belongs to the giant South American species, and even there it is uncommon.

Natural predators: the specialist is the tarantula hawk wasp (Pepsis and relatives), which paralyses an adult tarantula, drags it into a burrow and lays a single egg on it. Coyotes, skunks, ringtails, roadrunners, snakes, lizards and parasitic flies take the rest, and a wandering male is the most exposed animal in the desert on the night he leaves his burrow.

Prey-predator dynamics: a scrub hillside may hold dozens of burrows, each removing insects every night, while the tarantulas themselves feed a guild of vertebrate predators and parasitoids. They are middle links in an arid food web with few other large invertebrate predators.

Seasonal behaviour: females plug their burrows through cold or drought and can go months without feeding. Males mature after eight to ten years, leave their burrows for good and walk by night in search of females — the origin of the late-summer tarantula "migrations" of the American southwest. A male rarely survives a year after that final moult; a female may live twenty to thirty years.

Relationship with humans: harmless and useful. The genus is kept in captivity precisely because it is slow and placid, but wild collection and roadkill during the male walking season are real pressures on local populations. The species has not been assessed by the IUCN.

Similar tarantulas and how to tell them apart

Quick facts

Did you know?

• A tarantula that loses a leg can grow it back. The replacement appears at the next moult, shorter and thinner than the original, and reaches full size after another moult or two.
• The "tarantula dance" often described for this genus is really two behaviours: the defensive rear, in which the spider lifts its front legs and body to expose the fangs, and the male's courtship drumming at a female's burrow entrance.
• Aphonopelma is the largest tarantula genus in North America, and the 2016 revision of its US species used DNA alongside anatomy to cut a long list of doubtful names down to twenty-nine.
• A moulting tarantula lies on its back for hours and looks dead. It is the most vulnerable moment of its life, and a spider disturbed then can be injured beyond recovery.

In summary, Aphonopelma caniceps is a patient, long-lived burrowing tarantula of dry Mexican country. It is no danger to anyone, its bald abdominal patch is a record of its own defensive hair-kicking, and the sensible precaution around it has far more to do with your eyes than with its fangs.