Maevia

Physical description and identification

Maevia is a genus of small jumping spiders in the family Salticidae, the largest family of spiders in the world. Between eight and ten species are recognised: most are North American, a few Chinese or Korean. The genus was erected by Carl Ludwig Koch in 1846 and sits in the tribe Dendryphantini, the same lineage as the much larger Phidippus jumpers. One correction is worth making at the start, because the error is repeated widely: Maevia is not an Indonesian or Pacific group. Its centre of diversity is temperate North America.

Adults

• Size: small. Adult body length runs roughly 4–8 mm, with females consistently larger and heavier than males. In Maevia inclemens, the best-studied species, females measure 6.5–8.0 mm and males 4.75–6.5 mm.
• Colour: browns, beiges, black and white, usually with pale chevrons down the abdomen and darker bands along each side. Fine coloured scales shift the apparent colour with the viewing angle.
• Eyes: eight in four pairs around a squared-off face. The front-central pair is enormous and tube-shaped and supplies the acute image that defines the family; the small side eyes cover a near-panoramic field and act as motion detectors. See spider eyes.
• Build and legs: a compact, slightly flattened body, a carapace highest just behind the eyes, thickened front legs used in display, and short, powerful rear legs that supply the jump.
• Distinctive features: male dimorphism in M. inclemens, where males occur in two forms that look like different species — black with three head tufts, or striped black and white with orange pedipalps. Species-level identification still depends on adult genitalia under a microscope.

Eggs and egg sac

Females build a small silk nest in a rolled leaf, a bark crevice or a sheltered corner of a fence, and lay pale round eggs inside a thick, papery white sac. The mother guards the sac in place rather than carrying it, and because the nest is closed on all sides, egg sacs are almost never seen in the open.

Spiderlings

Spiderlings hatch inside the nest, pale and translucent, and remain there through their first moult. Dispersal happens early in life, as small juveniles, not on reaching maturity — a point many older accounts get backwards. Young Maevia hunt exactly as adults do from the moment they leave, and grow through a series of moults inside fresh silk retreats.

Hunting, and why there is no capture web

Maevia spiders build no snare of any kind, and no jumping spider does. Silk is still central to their lives — nests, moulting chambers, egg sacs, winter retreats and, above all, the dragline anchored to the surface a moment before the spider leaps, which catches a missed jump and doubles as a rudder in mid-air. The leap itself is hydraulic: spiders have no extensor muscles at some leg joints, so they force haemolymph into the legs, which snap straight and launch the animal several body lengths. Hunting is a slow visual stalk with a fast finish — movement caught by the side eyes, a swivel to bring the big front eyes on target, a creep into range, then the jump. For the contrast with genuine web-builders, see our guide to spider webs.

Where Maevia spiders live

The genus is essentially North American. Maevia inclemens, the species almost everyone means when they say Maevia, ranges across the eastern and central United States and into southern Canada, from Ontario, Quebec and Manitoba south to the Gulf states and west to Texas. Other North American species are patchier and several are known from few collections; the Asian members occur in China and Korea and remain poorly studied.

Within that range these are spiders of sunlit vegetation and vertical surfaces: shrubs and low trees, woodland edges, vines and ivy, old fields and gardens, and very often the artificial surfaces people supply — fence rails, deck posts, window frames, siding and garden furniture.

They are strictly daytime animals. Activity peaks on warm, bright mornings and afternoons; in dull weather and at night the spider sits in a silk retreat. In the northern part of the range juveniles overwinter in those retreats under loose bark or in curled leaves and mature the following spring.

Are Maevia spiders venomous?

Yes, in the sense that nearly every spider is venomous: Maevia uses venom to subdue the small insects it catches. That venom is not medically significant to people or pets, no serious envenomation has ever been attributed to the family, and there is no antivenom for any jumping spider because none is needed.

The venom is tuned to insect nervous systems and delivered in tiny quantities, and these are 5–8 mm spiders whose fangs can barely engage human skin. Maevia belongs to the Salticidae, an entirely harmless family — not related to the recluse spiders or the widow spiders that account for genuine spider-bite medicine.

Can Maevia spiders bite?

They can, but it is rare and entirely defensive. A jumping spider that notices a human turns to face it — the swivel that makes salticids look so alert — and then walks away, drops on its dragline or jumps clear. Biting happens only when the spider is pressed against skin: squeezed inside a glove or pinned while being brushed off.

The result is a brief pinprick with a small red mark, sometimes a little itching, gone within a few hours. Wash the site with soap and water and apply a cold pack if it is uncomfortable; no creams, home remedies or medical treatment are needed. Seek advice only if redness or swelling spreads well beyond the bite, which points to a rare allergic response or an ordinary skin infection rather than to the venom.

Ecological importance and behavior of Maevia spiders

Maevia spiders are active, visually guided predators of small insects, hunting in a layer of the habitat that web-builders cannot use: the open, sunlit upper surfaces of leaves, walls and fence rails. A population working a hedge or a garden bed removes a steady stream of flies, leafhoppers, small moths, aphids, plant bugs and other spiders through the warm months.

Courtship: because females judge males by sight, courtship is a visual performance — waving and beating the front legs, raising the pedipalps, edging sideways, and in M. inclemens two entirely different routines for the two male forms. Experiments in which females watched video-recorded males found no preference for either morph; what draws attention is movement.

Natural predators: birds take them in the open, and so do lizards, mantises, assassin bugs and robber flies. Mud-dauber wasps and spider wasps (Pompilidae) paralyse small salticids to stock their nest cells, and larger spiders — including other jumping spiders and crab spiders waiting on flowers — are a constant hazard.

Prey-predator dynamics: the vision that makes Maevia an effective hunter is also its first line of defence, and the dragline is its escape route: a threatened spider drops instantly and hangs below the leaf until the danger passes.

Seasonal behaviour: the cycle is annual. Juveniles overwinter in silk retreats, mature in late spring, and breed through early and mid summer; adults are gone by autumn.

Relationship with humans: harmless and useful. They do not infest houses, build no webs in corners and damage nothing. A Maevia indoors has come in by accident and is best cupped and put outside on a plant.

Species in the genus and similar spiders

Quick facts

Did you know?

• Jumping spiders have the finest spatial vision known in any animal of their size — sharper than a cat's. The main eyes have a layered retina that the spider physically moves behind a fixed lens, scanning an image the way you would move a torch beam across a wall.
• Maevia inclemens is one of very few spiders in which males come in two distinct forms at roughly equal frequency, each with its own courtship display. Both are equally successful, which is why neither has replaced the other.
• The leap is hydraulic. Because spiders lack extensor muscles at certain leg joints, a jumping spider extends its rear legs by pumping body fluid into them under pressure, working together with the leg muscles — and it fixes a silk dragline first, which catches a missed leap and trims its body angle in flight.
• Salticidae is the largest spider family on Earth, with more than 6,000 described species.

In summary, Maevia is a small, harmless, web-free North American genus whose members hunt by eyesight and leap on a silk line — worth knowing for one species alone, the dimorphic jumper.