Eriophora

Physical description and identification

Eriophora is a genus of bulky, nocturnal orb-weavers in the family Araneidae. About a dozen species are currently recognised, split between the Americas and Australasia, and the genus name is Greek for "wool-bearing". They are not brightly coloured spiders. Almost everything about an Eriophora — the mottled bark tones, the lumpy outline, the habit of sitting still all day — is built around not being seen.

Two corrections are worth making at the start. The genus was erected by the French arachnologist Eugène Simon in 1864, not 1895, a date that is widely repeated online. And the Australian garden orb-weavers traditionally placed here have been the subject of a recent revision that moved them into a separate genus, Hortophora; most field guides and websites, including the species pages on this site, still use the older Eriophora names.

Adults

• Size: the genus spans a wide range. Large females such as E. ravilla reach about 20–25 mm in body length; smaller species sit nearer 10–15 mm. Males are consistently smaller and lighter than the females they court, often by half.
• Colour: off-white, cream, tan, rust, grey-brown or near black, usually mottled and often with a paler leaf-shaped folium on top of the abdomen. Colour varies so much within one species that it is nearly useless for identification.
• Eyes: eight small eyes in two rows, the side pairs set close together on small raised mounds. Like most araneids they see poorly and read the world through the web.
• Distinctive features: a large, humped or shouldered abdomen that overhangs the carapace, short and noticeably thick legs armed with strong spines, and a dense covering of fine hairs. Several species carry a pair of blunt tubercles on the shoulders of the abdomen. Species-level identification needs adult genitalia under magnification.

Eggs and egg sacs

Females spin a silken cocoon of several hundred eggs in late summer or autumn and fix it to bark, foliage or a sheltered corner of a building. In the warmer parts of the range a female may make more than one. She usually dies shortly afterwards; the eggs and the young inside the sac are what survive the cold season.

Spiderlings

Spiderlings hatch as pale, almost translucent miniatures and stay together on a communal tangle of silk for a few days. They then disperse by ballooning, releasing a thread of silk into the breeze and drifting away, which spreads a single brood over a wide area and prevents siblings competing for the same insects. They mature over a summer through a sequence of moults.

The web

The web defines the genus. At dusk the spider leaves its daytime retreat, lays a bridge line, and constructs a complete vertical orb, often a metre or more across and slung high between trees, fences, verandah posts or street lights. She sits head-down at the hub through the night. Before first light she eats the whole web, digesting and re-using the silk proteins, and retreats to a curled leaf, a twig or a crack where her mottled colouring makes her almost invisible. Rebuilding nightly costs energy but guarantees a clean, fully sticky trap every evening — see our guide to spider webs.

Where Eriophora spiders live

The genus has a curiously split distribution. One group lives in the Americas: E. ravilla from the southeastern United States through the Caribbean to Brazil, plus E. edax, E. nephiloides and E. fuliginea in Central and South America. In the United States the tropical orb-weaver is essentially a Gulf and subtropical species, common in Florida and southern Texas and scarce farther north.

The second group is Australasian. E. transmarina and E. biapicata are found across Australia, and E. pustulosa occurs in Australia and New Zealand. A single described species, E. neufvilleorum, is African. Older sources sometimes claim the genus is present throughout Africa; the evidence for that is thin.

Habitat is consistent wherever they occur: open woodland, forest margins, scrub, orchards, suburban gardens and parks — anywhere with two anchor points a metre or two apart and a steady supply of night-flying insects. They are strongly drawn to porch lights, street lamps and lit shop fronts, and a single well-lit doorway can support the same spider all summer.

Are Eriophora spiders venomous?

Yes, in the ordinary sense that applies to almost every spider: the venom exists to subdue moths, beetles and other insects caught in the orb. It is not medically significant to people or pets. No Eriophora species has an antivenom, none needs one, and no serious envenomation has been recorded from the genus anywhere in its range. These are araneid orb-weavers, unrelated to the widow spiders, the recluses or the Australian funnel-webs, and they lack the venom components that make those groups a medical concern.

Can Eriophora spiders bite?

They can, but they almost never do. A spider dropped onto a shoulder by a broken web will try to run or drop away on a dragline rather than turn and fight. Most recorded bites come from a spider being pressed against skin — trapped in clothing taken off a line, or gripped in a bare hand.

The result is a sharp pinprick with a little local redness and swelling that fades within a day. Wash the area with soap and water and use a cold pack if it stings. There is no need for antivenom, antibiotics or any other treatment. Seek medical advice only if the swelling spreads well beyond the bite or you develop hives or breathing difficulty, which would indicate an allergic reaction rather than the venom itself.

Ecological importance and behavior of Eriophora spiders

These are patient, energetically expensive predators. Building an orb of this size every night consumes a substantial share of the protein the spider takes in, which is exactly why the old web is eaten rather than abandoned. In return the spider gets a trap in perfect condition every evening, positioned wherever the insects were flying yesterday — an Eriophora will move site if the catch is poor.

The diet is dominated by night-flying insects: moths, beetles, mosquitoes, flying ants, midges, crane flies and cicadas. A spider that catches something too large simply cuts it free rather than wrecking the whole web. Around houses this makes them useful neighbours, since the same porch light that draws moths draws the spider that eats them.

Natural predators: mud-dauber and spider-hunting wasps are the main threat, paralysing adults to provision their nests. Birds take spiders caught in the open at dawn, and geckos and larger spiders take their share. Hiding motionless through daylight is the genus's main defence.

Prey-predator dynamics: by working the night shift, Eriophora uses a food supply that the day-active Argiope garden spiders and the orb weavers around them cannot reach, and shares its niche most closely with Neoscona, which has the same nocturnal habit at a smaller size.

Seasonal behaviour: in temperate parts of the range these are annual spiders. Spiderlings appear in spring, mature through summer, and the large webs of autumn belong to the biggest females of the year. Males stop web-building on maturing and wander, courting from the web edge by plucking the silk before approaching.

Relationship with humans: benign and useful. The only real friction is the web strung across a doorway overnight, and because the spider removes it each morning, trimming the anchor points in daylight usually settles the problem without harming anything.

Species in the genus and similar spiders

Quick facts

Did you know?

• The name Eriophora comes from the Greek for "wool-bearing", a reference to the woolly look of the silk these spiders wrap around large prey.
• Eating the old web is not tidiness but economics: the silk proteins are digested and recycled into the next night's orb, and a spider can recover most of the material within hours.
• Because the web is gone by sunrise, the same porch can look spider-free every morning and be crossed by a metre of silk every night all summer.
• Colour variation within one species is extreme — a single E. ravilla brood may include cream, rust, grey and near-black individuals.
• Australian garden orb-weavers, long placed in this genus, have been moved by recent revision into Hortophora; the older names remain in almost universal use in the field.

In summary, Eriophora is a small genus of large, plain, strictly nocturnal orb-weavers that quietly remove enormous numbers of night-flying insects. They are harmless, they are gone from view by breakfast, and the fresh web you walk into on a summer evening is the clearest sign they are there.