Phidippus arizonensis

Physical description and identification

Phidippus arizonensis is one of the plainer members of Phidippus, a genus better known for its scarlet and orange species. It is a compact, alert spider with the unmistakable build of the Salticidae: a tall, blunt-fronted carapace carrying two very large forward eyes, short heavy legs and a coat of fine scales and hairs. Where its famous relatives advertise, this one hides — its colours are the greys, browns and golds of dry bark, seed heads and stone.

Adults

• Size: the figure usually quoted for the species is about 4–6 mm (0.16–0.24 in) in body length, which would make it one of the smallest members of a genus whose species more often run 8–15 mm. Published measurements for arizonensis are limited, and larger individuals are likely; treat the small figure as an indication rather than a firm ceiling.
• Colour: the carapace is black, broken by white or cream markings along each side that form a pale border around the eye region. The abdomen is grey to grey-brown, usually with a darker spot or blotch toward the rear and faint paler chevrons in front of it.
• Legs: golden to tan, contrasting with the darker body, and thickly clothed in setae — the fine hairs and flattened scales that carry colour, register touch and air movement, and give the spider its grip on landing.
• Eyes: eight in four pairs. The two central forward eyes are enormous for the animal's size and provide sharp, colour, image-forming vision, while the smaller side and top eyes work as wide-angle motion detectors covering nearly the whole circle around the body. See our guide to spider eyes.
• Other features: the chelicerae carry the iridescent sheen typical of the genus, and mature males are slimmer, with longer front legs and the swollen pedipalps used in courtship and mating.

Eggs and egg sac

Females of this species are reported to use the dried seed heads and seed capsules of native prairie forbs as nest sites, spinning a silk chamber inside the hollow and laying the egg sac within it. The structure is dry, concealed and off the ground — a good defence against ants and damp — and the mother stays with the clutch instead of abandoning it.

Spiderlings

The young hatch inside the maternal chamber and remain there through the first stage of their lives, sheltering by night and, as they grow, venturing out by day. They leave to build their own small silk tents once they are large enough to hunt independently. Growth proceeds in steps, and every moult is carried out inside a sealed retreat because a newly moulted spider is soft and helpless for hours. The whole cycle from egg to adult takes most of a year.

Hunting and the use of silk

No capture web is built. The spider hunts on foot in daylight: the side eyes register movement, the body swings round to bring the principal eyes onto the target, and the spider closes in before launching itself. Silk is fixed to the surface as a dragline before every jump, so a missed target leaves the spider dangling instead of falling. The leap is hydraulic — spiders lack extensor muscles at the key leg joints and straighten the hind legs by forcing body fluid into them under pressure. Away from hunting, silk goes into small, flattened tent-like retreats spun under rocks, logs and loose bark, which are used for resting, moulting and egg-laying.

Where Phidippus arizonensis lives

Despite the name, this is not a spider confined to one state. Records run through the southwestern borderlands — Arizona, New Mexico and Texas in particular — and continue south into Mexico. The species epithet records the region the first specimens came from rather than the limits of its range.

Habitat is open, sunny and semi-arid: oak woodland and its edges, upland prairie and grassland, brushy slopes and rocky ground. The spider hunts on low vegetation, among grass and forb stems and across rock and bare soil, and shelters in silk tents under stones, fallen wood and slabs of bark. Like all salticids it needs sun — the visual system that makes it a hunter only works in good light — so it is most often seen on warm, bright days and stays sealed in its retreat in cold or wet weather.

Are Phidippus arizonensis spiders venomous?

Yes, in the sense that virtually all spiders are venomous: it has venom glands and uses them to subdue insects. The venom has no medical significance for humans or pets. No jumping spider anywhere in the world produces a dangerous bite; the venom is tuned to small arthropods and the quantity a spider this size can deliver is tiny. It is entirely unrelated to the recluse and widow spiders, the only groups in the region whose bites justify concern.

Can Phidippus arizonensis spiders bite?

It can, in self-defence, but it very rarely does. A spider of 4–6 mm has fangs that struggle to penetrate human skin at all, and its instinct on meeting something as large as a person is to watch, then step aside or drop away on its dragline. Bites happen only if the spider is pressed — caught inside clothing, closed in a hand, or squeezed while being brushed off.

The result is a momentary prick, perhaps a pinpoint of redness or a small itchy spot, and nothing more. Wash the area with soap and water and apply a cold pack if it stings. Medical advice is warranted only in the rare case of spreading swelling, hives or breathing difficulty — signs of an allergic reaction rather than of the venom — or if the site later looks infected.

Ecological importance and behavior of Phidippus arizonensis

This is a daytime visual hunter with the stop-start walk characteristic of a spider that scans between steps. It patrols low vegetation and rock in bright sun, stalks prey to within a jump, and takes it with the front legs thrown forward to grip. Its small size means it works a different slice of the insect world from the big red Phidippus of the same country, taking prey that larger hunters ignore.

Diet: small flies, leafhoppers and other true bugs, small moths, beetles, ants and other spiders. As a predator of leafhoppers and small plant-feeding insects it does real work in grassland and rangeland.

Natural predators: insect-eating birds, lizards, mantises, robber flies, ants, larger spiders, and the spider-hunting wasps that paralyse salticids and seal them into nest cells for their larvae.

Courtship: males locate females by following their draglines and then display in front of them — front legs raised and waved, body rocking, abdomen vibrating. Everything hinges on the female's response; an unreceptive one drives the male off, and the approach is genuinely risky for him.

Seasonal cycle: juveniles overwinter part-grown in silk retreats, mature in spring, and adults are seen through the warm months. One to two years is a typical lifespan for a spider of this group.

Relationship with humans: it keeps to natural habitat and rarely enters houses. It is harmless, useful, and best left where it is found.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The species was described in the 1880s by George and Elizabeth Peckham, the American husband-and-wife team whose work on jumping spiders first documented their elaborate courtship displays.
• A jumping spider's principal eyes focus by moving the retina rather than the lens: muscles swing the tube-shaped back of each eye behind a fixed lens to scan the image, the way a person moves their eyes.
• Salticids see colour, and several species are known to detect ultraviolet light that is completely invisible to us — part of why their courtship displays look plainer to human eyes than they do to the spiders.
• Nesting inside dried seed capsules is an elegant piece of engineering: the shell is waterproof, already hollow, hard for ants to enter, and held clear of the ground.

In summary, Phidippus arizonensis is a small, cryptic, entirely harmless hunter of southwestern grassland and oak country. It builds no snare, poses no risk to people, and spends its short life doing quiet pest control among the grass stems — visible mainly to those who look closely enough to notice a pair of dark eyes looking back.