Western Spotted Orbweaver Spider (Neoscona oaxacensis)

Physical description and identification

The western spotted orbweaver is a solid, round-bodied araneid built for sitting in a web rather than running. The abdomen is broadly oval and widest at the shoulders, the carapace is low and grey-haired, and the legs are thick, strongly spined and ringed with dark bands. From above the impression is of a grey-and-cream marbled spider with a dark zigzag stripe down the middle of the back — the feature behind the old regional nickname "zigzag spider".

Adults

• Size: females measure roughly 9–18 mm in body length, males 6–13 mm. A large female with her legs spread covers a matchbox, making her one of the bigger orb weavers seen in the western states.
• Colour and pattern: the upper abdomen carries a mottled folium of black, chalky white and cream, usually with paired pale shoulder patches, a dark central band broken into chevrons and white flecks along the sides. The underside is charcoal with two pale streaks flanking the spinnerets. Colour is highly variable rather than literally unique to each spider: two individuals from one hedgerow can look quite different, while siblings from a single sac often match.
• Legs: boldly banded in alternating dark brown and pale grey with conspicuous black macrosetae — the quickest way to separate Neoscona from the more uniformly reddish legs of many Araneus species.
• Regional variation: South American spiders tend to be narrower and darker than the broad, pale North American form.
• Sexes: mature males are smaller and longer-legged, with swollen palps, and abandon web-building to search for females at the end of summer.

Eggs and egg sac

Females mate in late summer and lay in autumn. The eggs go into a rounded, papery sac of pale silk tucked under a leaf, a fence rail or a curl of bark near the web, several hundred to a sac. It is the eggs and the newly moulted spiderlings that spend the winter inside, not the adult — most adults die with the first hard frosts. In frost-free parts of Mexico and Central America the species breeds through much of the year.

Spiderlings

Spiderlings hatch inside the sac, moult once and stay clustered until warm spring weather triggers them to chew their way out. They disperse by ballooning, then build miniature orbs a few centimetres across. Each later moult adds size and pattern, and a spiderling that hatches in March may be a full-sized female by August.

The web

The web is a classic vertical orb, tidy and close-meshed, often 40–60 cm across and slung between fence wires, irrigation pipes, reeds, shrubs or the corner of a shed. There is no stabilimentum — the ribbon of dense silk that Argiope spiders weave through the hub. That absence is normal for the family: stabilimenta are a speciality of a few genera, and no Neoscona makes one. The hub is left open and the spider hangs head-down in it at night; many individuals also sit in the web by day, while others retreat to a curled leaf at the end of a signal line. Webs are rebuilt frequently, usually at dusk, and the old silk is eaten and recycled. For how the sticky spiral is laid down, see our guide to spider webs.

Where the western spotted orbweaver lives

Neoscona oaxacensis is a spider of the warm, dry western half of the Americas. In the United States it is common from California and Oregon east across the Southwest to Texas and Kansas, and it continues south through Mexico and Central America into Colombia, Ecuador, Venezuela and Peru. It also reached the Galápagos Islands, where it is one of the most conspicuous web-builders on the coastal lowlands.

Its preferred setting is open country with sparse vegetation and something solid to anchor a large web to: field margins, canal and ditch banks, desert washes, coastal scrub, road verges and the outsides of barns, sheds and pump houses. Irrigated farmland suits it especially well, and in California cotton, alfalfa and citrus it reaches high densities in late summer, with webs strung a metre apart along a whole row. It is not a house spider and does not breed indoors, though a wandering male may end up on a porch in autumn.

Are western spotted orbweaver spiders venomous?

Yes — like almost all spiders it uses venom to immobilise the insects it catches. That venom is tuned to flies, moths and beetles and has no medically significant effect on people or pets. The western spotted orbweaver is unrelated to the recluse and widow spiders and carries none of the tissue-damaging enzymes or potent neurotoxins that make those groups a genuine medical problem. No verified case of serious envenomation by any Neoscona has been published.

Can western spotted orbweaver spiders bite?

It can, but it very rarely does. An orb weaver's defensive repertoire is built around escape: when the web is jarred it drops on a dragline, shakes the web to blur its outline, or runs for the retreat. Bites happen almost exclusively when a spider is squeezed — caught in a sleeve, trapped in a glove or grabbed off a fence post.

A bite feels like a pinprick or a mild bee sting: a small red mark, brief local pain and perhaps a few hours of itching, gone within a day. Wash the area with soap and water, apply a cold pack and keep it clean. Seek medical advice only if the redness spreads, the pain worsens after the first day, or you show signs of an allergic reaction such as hives or breathing difficulty — those point to infection or allergy, not to the venom.

Ecological importance and behaviour of the western spotted orbweaver

This is a sit-and-wait predator whose entire hunting strategy is the web. Suspended at the hub, the spider holds the radials with its front legs and reads the vibration signature of anything that hits the sticky spiral. Small prey is bitten at once; a wasp or a grasshopper is wrapped in silk first and bitten afterwards, and anything too big is simply cut free to spare the web.

Diet: flies, midges, mosquitoes, moths, small beetles, leafhoppers, plant bugs and winged ants. In cotton and alfalfa that catch includes a long list of crop pests, and integrated pest management programmes in the Southwest count N. oaxacensis among the useful generalist predators in the system.

Natural predators: mud-dauber and spider-hunting wasps paralyse orb weavers to provision their nests, wrens and gnatcatchers pick them straight from the hub, and lizards, mantids and larger spiders take them opportunistically. Parasitoid wasps also lay eggs on the abdomen and eventually hijack the spider's web-building for their own cocoon — see what eats spiders.

Seasonal rhythm: spiderlings appear in spring, grow through early summer and mature in July and August. September and October are the months when webs are biggest and females heaviest with eggs, which is when people most often notice the species. Males stop feeding, wander and die soon after mating; females survive until cold weather.

Living alongside people: harmless and useful. Where a web is in the way, brushing it down is enough; insecticides only cost you free pest control.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The Baltic German arachnologist Eugen von Keyserling described the species in 1864 from Mexican material; the species name refers to the state of Oaxaca.
• It is one of very few mainland American orb weavers to have colonised the Galápagos archipelago on its own, and it is now a familiar sight in the islands' arid coastal zone.
• In irrigated farmland the webs can be packed so closely along a fence line that they form an almost continuous curtain — not a social colony, just many independent spiders exploiting one insect flyway.
• The genus name Neoscona, coined by Eugène Simon in 1864, combines Greek roots meaning "spin" and "reed" — a nod to the neat, closely woven orb. Browse the group on our Neoscona page.

In summary, the western spotted orbweaver is a large, harmless, marbled orb weaver of the open West that removes thousands of flying insects from a field edge every season. Learn its banded legs and open, zigzag-free hub and you will recognise it at a glance among the other orb weavers.