California Ebony Tarantula (Aphonopelma eutylenum)

Physical description and identification

The California ebony is a solid, heavy-bodied tarantula with the downward-striking fangs of all Mygalomorphae. The common name suits mature males better than females: males darken to a deep chocolate or near-black, while females stay a plainer beige-brown with a darker abdomen. Any large hairy spider walking a California trail on an October evening is most likely this species.

Adults

• Size: body length runs from about 25 to 44 mm, roughly 1 to 1.7 inches, measured from the front of the carapace to the spinnerets. Across the outstretched legs a big adult covers some 10–13 cm.
• Colour: females are beige to mid-brown on the carapace and legs with a distinctly darker, sometimes black abdomen. Mature males are darker overall and often close to black, with proportionally longer, thinner legs and a much smaller abdomen. Freshly moulted animals look far richer in colour than worn ones, whose hairs have faded in the sun.
• Eyes: eight small eyes clustered on a raised tubercle at the front of the carapace. Eyesight is poor even by spider standards, so the animal reads its world through sensory hairs rather than vision.
• Other features: abdomen and legs are densely covered in setae. Those on the abdomen include urticating hairs, the barbed defensive bristles New World tarantulas kick off with a hind leg. A bald patch on the back of the abdomen shows where hairs have been shed; it appears in both sexes and is a sign of use, not a male-only trait. Mature males are told by their swollen pedipalps and by the small hooks on the front legs used to hold a female's fangs during mating.

Eggs and egg sac

The female mates in autumn, stores the sperm through winter and lays in late spring or summer inside her burrow. The eggs go onto a silk mat that she folds into a sac and guards continuously, turning it so the contents are aired evenly. A sac may hold several hundred eggs, and the female rarely leaves it until the young disperse.

Spiderlings

Hatchlings are greyish-white and soft. They remain near the mother for a short time, then leave to dig their own pencil-width burrows in the surrounding ground. Colour and size build slowly: each stage ends in a moult, and females take several years to mature. During a moult the spider lies on its back, helpless for a day or more, which is why an undisturbed burrow matters so much.

The burrow and hunting

This is a burrowing spider. It digs a silk-lined tunnel, often under a rock, a log or a grass tussock on a well-drained slope, and lays a thin scatter of silk across the entrance. That silk is a sensor, not a snare: it carries the footsteps of a beetle or cricket to the waiting spider, which lunges out, bites and drags its prey below. Nothing about it resembles the aerial traps described in our guide to spider webs.

Where the California ebony tarantula lives

Aphonopelma eutylenum is essentially a California species. It occupies the Coast Ranges, the inner valleys and the western Sierra Nevada foothills from roughly the San Francisco Bay Area south, and it is the tarantula people meet in places such as Mount Diablo, Henry W. Coe State Park and the Pinnacles country.

It is worth correcting a claim that appears in many older accounts. This is not a desert tarantula. Its habitat is oak woodland, chaparral, grassland and scrub on hillsides with deep-enough soil for a burrow, in country that gets a genuine wet winter. The tarantula of the Mojave and the Great Basin — in Nevada, Arizona and the California deserts proper — is the desert tarantula, Aphonopelma iodius. The large 2016 revision of United States Aphonopelma reassigned a great many records that had once been filed under eutylenum, so range statements published before then should be treated with care.

Where it does occur it can be locally abundant, with dozens of burrows on a single south-facing slope. It shares California with Aphonopelma johnnycashi of the Sierra Nevada foothills, and is replaced eastward by species such as the Arizona blond and the Grand Canyon black tarantula.

Are California ebony tarantulas venomous?

Yes, but mildly so. Like almost all spiders it carries venom, and it uses it to subdue insects. No Aphonopelma species is medically significant to humans, and the California ebony is among the gentlest of them. Its venom has neither the tissue-damaging enzymes of the recluse spiders nor the powerful neurotoxins of the widow spiders, both of which also live in California and are the species that actually warrant caution.

The urticating hairs deserve more respect than the fangs. Barbed and easily shed, they cause an itchy, nettle-like rash in skin that can last for days, and if they reach the eye they cause a real injury needing medical attention. Do not handle a tarantula near your face.

Can California ebony tarantulas bite?

They can, but they are notably reluctant to. This is a docile species that reacts to disturbance by walking away or dropping into its burrow, and that will flick urticating hairs long before it uses its fangs. Bites essentially only happen when the spider is grabbed, trodden on or trapped against skin.

The fangs are large, so the main effect is mechanical: a deep double puncture, sharp local pain, a little bleeding, and redness and swelling that ease over several hours. Wash the area with soap and water, use a cold pack, elevate the limb and take a simple analgesic if needed. Watch the wound for infection over the following days, and seek medical care if the pain worsens rather than settles, if swelling spreads, or if there is breathing difficulty, faintness or a widespread rash — signs of an allergic reaction rather than of the venom. No antivenom exists or is needed.

Ecological importance and behavior of the California ebony tarantula

The California ebony is a nocturnal ambush predator with a very slow metabolism. It waits at the mouth of its burrow after dark and takes whatever walks past: beetles, cockroaches, crickets, grasshoppers, mantises, millipedes and occasionally a small lizard. An adult can go weeks between meals and draws most of its water from prey and from the damp burrow walls.

Natural predators: the specialist is the tarantula hawk wasp, which paralyses an adult spider with a sting and seals it alive underground as food for a single larva. Coyotes, skunks, raccoons, hawks, owls, roadrunners, snakes and large centipedes all take tarantulas as well, and wandering males are the most exposed of all.

Prey-predator dynamics: a hillside full of long-lived burrowers applies constant predation pressure on large ground insects through seasons when faster-living hunters have died back. In the other direction the spiders are a substantial, protein-rich food item for a long list of Californian vertebrates.

Seasonal behavior: the famous autumn tarantula walk runs from roughly September to November. Mature males abandon their burrows and travel, sometimes hundreds of metres a night, drumming at burrow entrances to find receptive females. A male who has reached maturity will not moult again and normally dies over the following winter. Females stay in their burrows and may live and breed there for two decades or more.

Relationship with humans: harmless and largely one-sided. The spiders do not enter houses and are no threat to pets. The pressures run the other way — road mortality during the autumn walk, loss of grassland and oak woodland to development, and collecting. Populations recover slowly because females take years to mature, so leaving burrows undisturbed matters more than it would for a short-lived spider.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• Ralph Vary Chamberlin described the species in 1940. Chamberlin and his collaborator Wilton Ivie named a very large share of the spider fauna of the American West.
• The 2016 revision of United States Aphonopelma reduced about fifty-five named species to twenty-nine, using DNA alongside anatomy and geography. A. eutylenum was upheld, but its range shrank considerably as desert populations were reassigned.
• Several California parks run guided autumn tarantula walks, timed to the weeks when males are on the move. It is one of the few places in the United States where a wild tarantula is a scheduled public attraction.
• A tarantula extends its legs hydraulically, using blood pressure rather than extensor muscles, which is why a dehydrated or freshly moulted spider moves so awkwardly — and why a curled-up posture is a bad sign.
• Females can regrow a lost leg over successive moults, a repair that stays available for the whole of their long adult life.

In summary, the California ebony tarantula is a patient, harmless resident of the state's oak hills and grasslands, more useful to people than it is dangerous, and most easily protected by leaving its burrows and its autumn wanderers alone.