Aphonopelma parvum

Physical description and identification

Aphonopelma parvum belongs to a small group of dwarf species inside Aphonopelma, the only tarantula genus native to the United States. It is a true theraphosid in every anatomical sense — downward-striking fangs, two pairs of book lungs, a dense coat of setae, a silk-lined burrow — simply built at a fraction of the usual scale.

That scale is worth stating plainly, because it is the fact most often mangled. Older summaries of this species quote a size of "60 to 122", a figure that has been reprinted with centimetres attached. No spider on earth approaches 60 cm, let alone 1.2 metres; the largest tarantula alive spans about 30 cm. The numbers are millimetre measurements of the whole animal at most, and in reality parvum is one of the smallest tarantulas in North America.

Adults

• Size: miniature. Adult leg span is on the order of 4–7 cm (about 1½–2¾ in) and body length is measured in millimetres rather than centimetres. Beside a desert tarantula it looks like a juvenile that stopped growing.
• Colour: both sexes are essentially black. Females often show browner legs against the dark body, and the whole animal carries a mix of long reddish-orange setae and much finer grey ones, so in sunlight the spider reads as black shot through with rust.
• Build: stocky and ground-adapted, with short, thick legs and scopulate (brush-tipped) feet. It is a walker and a digger, not a climber.
• Urticating hairs: present, as in every New World tarantula, and completely missing from most popular accounts of this species. The upper abdomen carries barbed setae that the spider kicks off with its hind legs when it cannot escape.
• Sexes: mature males are slimmer, longer-legged and carry club-shaped palpal bulbs plus tibial hooks on the front legs. Females stay heavier-bodied and keep the same form for the whole of their much longer lives.

Eggs and egg sacs

The female builds her egg sac inside the burrow, wrapping the eggs in a purse of silk that she turns and guards until the spiderlings emerge. A miniature species produces a correspondingly modest clutch — tens rather than the several hundred eggs of the large desert species.

Spiderlings

Newly emerged spiderlings are pale and faintly marked, darkening towards adult black over successive moults. They leave the mother's burrow on foot after a short period and dig their own tiny tunnels nearby. Miniature tarantulas reach maturity faster than the giants of the genus, but growth is still counted in years, not months.

The burrow and hunting

This species spins no capture web. Its silk lines the burrow, seals the entrance during cold or drought, forms the sperm web and wraps the eggs. What the older accounts describe as "silk threads to detect motion" is accurate and important: loose lines radiating from the burrow mouth act as trip-wires, and a passing ant, cricket or beetle plucking one brings the spider out in a rush. The prey is seized, bitten and dragged underground to be eaten.

Where Aphonopelma parvum lives

Aphonopelma parvum is a species of south-eastern Arizona, one of fourteen new tarantulas described from the United States in the 2016 revision that finally sorted the genus with DNA as well as anatomy. Popular summaries often add New Mexico to its range; that is a reasonable guess about a desert genus rather than a documented fact for this species, which is known from a restricted area of Arizona's sky-island country.

The habitat is arid to semi-arid ground with enough structure to shelter a small burrow: desert grassland, rocky slopes, oak and juniper margins at moderate elevation, and the gravelly soil around boulders and shrub bases. Small tarantulas are far more dependent on microclimate than large ones, because a small body dries out faster, so burrows tend to be placed where shade, stone and root cover hold humidity. Other members of the genus share the same landscape at very different sizes — the Arizona blond in the lower Sonoran Desert, A. saguaro and A. johnnycashi elsewhere in the southwest.

Is Aphonopelma parvum venomous?

It has venom and uses it to subdue insects, but the venom is not medically significant to humans or pets. No species of Aphonopelma has ever been linked to a death or a serious systemic illness, and no antivenom exists because none is required. A spider this small also carries very little venom and has fangs too short to do much mechanical damage.

The contrast with the Old World tarantulas is the useful one. Asian ornamentals such as Poecilotheria and the African baboon spiders have no urticating hairs and rely on venom potent enough to cause hours of cramping. The American genera traded that for barbed abdominal setae, which is why a New World tarantula's defence is something you wash off your hands rather than something you treat in hospital.

Can Aphonopelma parvum bite?

It can, but it is among the least likely spiders you will meet to do so. The temperament of the genus is placid and the first response to disturbance is to run for the burrow. If cornered it kicks urticating hairs; if that fails it rears into a threat posture; only a spider that is pinned or squeezed actually bites.

The result is trivial by tarantula standards: brief local pain, a pinprick pair of punctures, perhaps a little redness. Wash with soap and water, use a cold pack, and watch for infection or an allergic reaction rather than for venom effects. No home remedy, no heat, no suction.

Ecological importance and behavior of Aphonopelma parvum

Like the rest of its genus this is a sedentary ambush predator that spends daylight underground and waits at the burrow mouth after dark, legs resting on the silk lines. A female's entire adult life may play out inside a couple of square metres.

Diet: small arthropods scaled to the spider — ants, termites, small beetles, crickets, roaches and other spiders. Being miniature changes what it can handle; unlike the large desert species it will never take a lizard, and it depends on the abundant small-insect layer of the arid ground.

Natural predators: tarantula hawk wasps and other spider-hunting wasps, centipedes, scorpions, larger spiders, lizards, and ground-foraging birds. Small size cuts both ways: it removes the spider from a few predators' menus and adds it to many others'. Parasitic flies attack burrowing tarantulas throughout the genus.

Prey-predator dynamics: in arid systems the small-bodied predators do much of the quiet work of keeping insect numbers in check, and a dwarf tarantula occupies a niche that larger relatives cannot use. It is a middle link in the food web, not a top predator.

Seasonal behaviour: burrows are plugged through the cold months and the pre-monsoon drought, and activity peaks when summer rain brings out insects. Mature males abandon their burrows and walk at night in search of females, the most dangerous journey of their lives, and die within roughly a year of that final moult. Females live on for many years.

Relationship with humans: almost none. This is a small, cryptic, recently described spider with a restricted range, and that combination is exactly what makes a species vulnerable to habitat conversion and to collecting for the hobby. It has not been assessed by the IUCN.

Similar tarantulas and how to tell them apart

Quick facts

Did you know?

• The species was named in 2016 by Chris A. Hamilton, Brent E. Hendrixson and Jason E. Bond, in the same monograph that cut a long list of doubtful United States tarantula names down to twenty-nine valid species and added fourteen new ones.
• Parvum is simply the Latin for "small", and it is one of the few tarantula epithets that tells you immediately what the animal looks like.
• Dwarfism has evolved more than once in Aphonopelma. Several unrelated-looking miniature species live in the arid southwest, and DNA shows they are not all each other's closest relatives.
• Being small changes the whole life history: a miniature tarantula matures years earlier than a giant of the same genus, but it also dries out faster, which is why it is tied so tightly to sheltered microhabitats.

In summary, Aphonopelma parvum is a genuine tarantula in miniature — a black, rust-flecked burrower from a small corner of Arizona, harmless to people, defended by barbed hairs rather than by venom, and a useful reminder that a size figure repeated often enough is still wrong if it says a spider is a metre across.