Gray Cross Spider (Larinioides sclopetarius)

Physical description and identification

The gray cross spider is a medium-large, thickset orb weaver with a matte, velvety look rather than the glossy sheen of many araneids. The abdomen is broad and slightly domed, the legs sturdy and dark-banded, and the whole spider reads as grey at a glance — which is exactly how it disappears against weathered steel and concrete.

Adults

• Size: females measure about 10–14 mm in body length and males about 8–9 mm. Females are also far bulkier, and a gravid female in early summer looks almost spherical from the side.
• Colour and pattern: the ground colour is grey, though some individuals are brown or nearly black. The upper abdomen carries a dark leaf-shaped folium with a scalloped edge picked out by a fine white or cream margin, and a pale bar across the shoulders that forms the vague cross behind the common name.
• Carapace: the key field mark. Dense white hairs run around the edge of the head region, drawing a pale silhouette against the darker centre.
• Legs: grey-brown with darker rings and strong black spines, thicker at the base than in most orb weavers of the same size.
• Sexes: mature males are slimmer and longer-legged with swollen pedipalps. Unusually for an orb weaver, a male may share the edge of a female's web for days before mating.

Eggs and egg sac

Females produce several egg sacs through the warm months, each a flattened yellowish cushion of silk wedged into a crack in the metalwork, under a rail cap, behind a sign or inside the retreat itself. The female guards the sac and stays close to it. A single sheltered girder can hold a dozen sacs from different females.

Spiderlings

Spiderlings emerge after a few weeks in summer, disperse only a short distance and start building at once. Juvenile webs are noticeably more symmetrical than adult ones: as the spider grows, the capture area below the hub becomes larger than the area above it, because a heavy spider drops downwards to reach prey far faster than it can climb up. Young spiders hatching late in the season overwinter as subadults and mature the following spring.

The web

The web is a vertical orb that grows with its owner, reaching roughly 70 cm across in a large female. It is anchored to hard surfaces — girders, handrails, brickwork, lamp brackets — rather than to vegetation, and a short tubular retreat of dense silk sits at one upper corner, with a signal line running to the hub. The spider rests there by day and returns to the hub after dark.

Most of the orb is rebuilt at night, the damaged spiral eaten and replaced. Site choice is deliberate: offered lit and unlit places to build, this species settles on the lit ones, because lamps concentrate the midges it lives on. That preference has been demonstrated experimentally, and it explains why bridges, marinas and floodlit quaysides are the classic places to find it. Our guide to spider webs covers how the frame, radials and sticky spiral are laid down.

Where the gray cross spider lives

Larinioides sclopetarius is a Holarctic species, widespread across Europe from Scandinavia and the United Kingdom south to the Mediterranean and east through Russia into northern Asia. In North America it is considered an introduction from Europe and is now firmly established, most abundantly around the Great Lakes and the industrial waterfronts of the Northeast, in states such as Michigan, Ohio, Wisconsin and New York, as well as parts of Canada.

Wherever it occurs the pattern is the same: water plus a man-made structure. Road and rail bridges, canal locks, jetties, pontoons, boathouses, harbour railings, weirs and riverside walls are all prime habitat, and the spider is far less often found on plants. The reason is food: water produces enormous emergences of non-biting midges, and a web strung beside a lamp intercepts them by the hundred. Populations can be very dense, with webs less than a metre apart along a whole bridge rail — not a colony, simply many individuals tolerating close neighbours where prey is abundant enough to make territoriality pointless.

Are gray cross spiders venomous?

Yes, but only in the way every orb weaver is. The venom is used to immobilise midges, mayflies and moths and has no medically significant effect on people, pets or livestock. Larinioides spiders carry none of the tissue-damaging enzymes of recluse spiders and none of the neurotoxins that make widow bites a medical problem, and there is no record in the clinical literature of a serious reaction to a bite from this species.

Can gray cross spiders bite?

They can, but bites are genuinely rare. Because gray cross spiders live on railings and lamp posts people touch, the usual scenario is a spider trapped under a hand or inside a sleeve. Given any warning it drops out of the web on a dragline or bolts into its retreat.

A bite produces brief, sharp local pain, a small red mark and sometimes a little swelling or itching, all of it gone inside a day. Wash with soap and water, apply a cold pack, and keep the site clean. Seek medical advice only if the redness keeps spreading after 24 hours, the pain worsens instead of easing, or you develop hives, wheezing or dizziness — signs of infection or allergy rather than of the venom. Do not cut, burn or apply suction to a spider bite.

Ecological importance and behaviour

The gray cross spider is a nocturnal sit-and-wait predator with an exceptionally good sense of where food will be. It hangs head-down at the hub after dark, reads prey vibration through the radii and rushes out to bite or wrap. Everything about it — tolerance of neighbours, attraction to lamps, preference for waterside metalwork — follows from exploiting the mass emergence of aquatic insects.

Diet: chironomid midges above all, along with mayflies, caddisflies, mosquitoes, small moths, lacewings and flying ants. One female beside a bridge lamp can take hundreds of midges in a single summer night.

Natural enemies: the scuttle fly Phalacrotophora epeirae is a parasitoid whose larvae develop inside the spider's egg sacs, and the solitary wasp Trypoxylon attenuatum hunts the spiders themselves, paralysing them to stock its mud nest cells. Birds, bats taking the wandering males and larger spiders add further pressure. Between them these enemies keep even the densest bridge populations in check.

Seasonal rhythm: adults are present from late spring through autumn, with numbers peaking in mid to late summer. Subadults and some adults shelter through the cold months deep in crevices in the structure they live on and become active again in spring; see where spiders go in winter. Individuals can live well over a year, and a sheltered female may survive into a second season.

Relationship with people: entirely benign and quietly useful, since it removes large volumes of midges and mosquitoes from exactly the places people sit outside on summer evenings. Heavy webbing on painted steelwork is a maintenance nuisance and nothing more; washing it off is enough.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The species was described by the Swedish naturalist Carl Clerck in 1757, in Svenska Spindlar — the book that introduced binomial names for animals a year before Linnaeus, and the only pre-1758 work whose names are still valid in zoology.
• Its attraction to lamps is an active choice, not an accident — one of the clearest cases of a wild animal benefiting from light pollution.
• An adult's orb is deliberately lopsided, with more capture area below the hub than above it, because gravity lets a heavy spider reach prey downwards much faster than upwards.
• Males are unusually tolerant of one another, and several spiders often share one girder — behaviour that has made the species a favourite subject for laboratory work on spider learning and mate choice. See our overview of the genus Larinioides.

In summary, the gray cross spider is the classic urban waterside orb weaver: harmless, grey, fond of steel and streetlights, and responsible for removing an extraordinary number of midges from the air above a summer river.