Araneus ventricosus

Physical description and identification

Araneus ventricosus is the heavyweight of the East Asian Araneus orb weavers. Where the garden species of Europe and North America are colourful and obvious, this one is built to disappear: dark, matt, bulky and nocturnal. Most people who live inside its range have shared a wall with it for years without ever seeing the spider itself — only the web that appears across a doorway overnight and is gone by breakfast.

Adults

• Size: mature females measure about 20–30 mm in body length, making this one of the largest orb weavers in the region. Males are smaller but not dwarfs, roughly 10–17 mm; claims of a 7–8 mm male belong to a different species and are a long-standing error in popular accounts.
• Colour: variable shades of grey-brown, chestnut and blackish brown. The abdomen carries a darker leaf-shaped folium with a scalloped, paler-edged outline, and there is usually a pale band across the front of the abdomen. Legs are banded in dark and light brown. Pale straw-coloured individuals turn up occasionally.
• Eyes: eight eyes in two rows, the four median eyes forming a small square on a raised area, the lateral pairs set out at the corners. No eye is greatly enlarged.
• Distinctive features: a high, rounded, almost globular abdomen with slight shoulder humps, a broad short carapace, and stout legs armed with strong spines. Everything is covered in short setae, which gives the spider a dusty, matt look rather than a glossy one.

Eggs and egg sac

Females mate in late summer and lay in autumn. The egg sac is a loose, fluffy mass of pale yellow silk containing several hundred eggs, tucked under bark, roof eaves, bridge girders or a stone overhang rather than hung in the open. The female stays near it until she dies with the first cold spells.

Spiderlings

The young hatch and remain in the sac over winter, emerging in spring as a cluster of pale, dark-marked spiderlings with straw-coloured abdomens. They hang together for a day or two, then disperse on silk lines and begin building miniature orbs. Growth continues through the summer; in much of the range the species passes the following winter as a large juvenile in a crevice or in leaf litter, then completes its final moult in early summer.

The web

The web is a large vertical orb, commonly 50–80 cm across in an adult female and sometimes bigger, hung across open space between buildings, railings, branches or bridge structures. What makes it notable is the daily cycle: the spider builds after dusk, hunts through the night at the hub, and before dawn eats most of the silk back down, leaving only the frame lines and retreating to a hiding place at one corner. Recycling the silk protein saves the cost of rebuilding and keeps a conspicuous structure from standing in daylight. See our guide to spider webs for how the spiral is laid.

Where Araneus ventricosus lives

The species is East Asian and common through most of its range: Japan from Hokkaido to Kyushu, the Korean peninsula, much of China, Taiwan, and the far east of Russia. It is not native anywhere else.

Habitat descriptions that place this spider in leaf litter are misleading. Araneus ventricosus is an aerial, structure-loving spider: it needs two solid anchor points with a gap between them, and it finds them on house walls and window frames, under eaves and balconies, on bridges, fences, road tunnels and shrine buildings, and on tree trunks and woodland edges. Litter and loose bark matter only as winter shelter for juveniles and as a site for the egg sac. The species is at its most abundant in the mixed, semi-built landscape of villages and town edges, where structures for web frames and lights that concentrate insects sit side by side.

Is Araneus ventricosus venomous?

Yes, as nearly all spiders are: it needs venom to kill the insects it catches. It is not dangerous to people. Araneus venoms are built around insect-specific polyamine and peptide toxins and produce no systemic effects in humans; there are no confirmed cases of significant envenomation from this species or any of its close relatives, and no antivenom exists because none has ever been required.

Can Araneus ventricosus bite?

It can bite, and because a mature female is a large spider with fangs to match, a bite is felt. It is still a rare event. These spiders do not hunt on the ground, do not enter beds or clothing, and respond to disturbance by dropping out of the web on a dragline or bolting into the retreat. Bites almost always follow deliberate handling or the accidental crushing of a spider against skin.

Expect a sharp, localised pain like a deep pinprick, a small red mark and some swelling, all of which settle within a few hours to a day. Wash the site, apply a cold pack and keep it clean. Seek medical attention only if the wound shows signs of infection later, or if there are symptoms of an allergic reaction — spreading hives, swelling away from the bite, dizziness or breathing trouble.

Ecological importance and behavior of Araneus ventricosus

This is a nocturnal ambush predator with a strict daily routine. At dusk the spider leaves its retreat, checks or rebuilds the orb, and takes station at the hub or on a signal line running back to the hiding place. A struggling insect is located by vibration, run down, bitten first and then wrapped — the reverse of the Argiope sequence — and either eaten on the spot or carried to the hub.

Diet: night-flying insects above all — moths, caddisflies, midges, mosquitoes, beetles and lacewings — plus whatever daytime insects blunder into a web that has not yet been taken down. Webs built near outdoor lights intercept an enormous volume of insects, and a single large female can clear hundreds of moths and mosquitoes over a season.

Natural predators: birds find the spiders in their daytime retreats, mud-dauber wasps stock their mud cells with paralysed orb weavers, and parasitoid ichneumonid wasps lay eggs on the abdomen; the larvae of some of these wasps are known to manipulate their host into spinning a modified, reinforced web that supports the wasp cocoon. Geckos, mantises and larger spiders take their share too.

Mating and seasonal behaviour: males mature in early summer and leave their webs to find females, approaching along a mating thread and drumming a rhythm the female recognises. Females are largest in late summer and autumn, when they are building egg sacs. The species disappears entirely over winter, surviving as eggs, spiderlings and half-grown juveniles.

Relationship with humans: almost entirely positive, and closer than most people notice. The webs are built on human structures, the insects removed are the ones that bother us, and the spider itself is hidden all day.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The Japanese name onigumo means "demon spider", a reference to the size and the shoulder humps rather than to any danger.
• The species was described in 1878 by Ludwig Carl Christian Koch, a German arachnologist — not an entomologist, as is sometimes written. Spiders are arachnids, not insects.
• Its genome has been sequenced and its full catalogue of silk genes described, which has made Araneus ventricosus one of the reference species for research into artificial spider silk and high-performance fibres.
• Eating the old web is not tidiness. Silk proteins are expensive to make, and an orb weaver that recycles its web recovers much of that investment within hours through the gut.
• The species has a long history in East Asian folk medicine, which is why it appears in old Chinese and Japanese pharmacopoeias under its own name — a piece of cultural history rather than a recommendation.

In summary, Araneus ventricosus is a large, shy, nocturnal orb weaver that lives on the outside of East Asian buildings and works the night shift on moths and mosquitoes. If a huge web appears across your doorway overnight and vanishes by morning, this is the spider responsible.