Furrow (Larinioides cornutus)

Physical description and identification

The furrow spider is a medium-sized, plump-bodied orb weaver and the best known member of the genus Larinioides. Its colour is so variable that beginners often key the same species out twice, so identification rests on the shape of the abdominal marking rather than on the background colour.

Adults

• Size: females measure roughly 6–14 mm in body length and males 5–9 mm, so the sexes overlap far more than in most orb weavers. A well-fed autumn female is noticeably round and heavy.
• Colour: the ground colour ranges from pale grey and cream through yellow-brown to dark reddish brown or almost black, and the same population can contain all of them. What stays constant is the pattern: a pale central band down the top of the abdomen, edged on both sides by a dark, scalloped, wavy line. That leaf-shaped or furrow-shaped mark is what the common names refer to. The carapace is grey-brown with a darker median stripe, and the legs are faintly ringed.
• Eyes: eight eyes in two rows of four, the two middle pairs forming a small square and the side pairs set close together on each edge. Older accounts describing six eyes in a single row are simply wrong — no member of this family has six eyes, which is a feature of the recluse family instead. See our guide to spider eyes for the layout.
• Distinctive features: a rounded, slightly shouldered abdomen, short sturdy legs relative to body size, and a covering of fine hairs that give a velvety look. Males are slimmer with longer legs and obvious swollen pedipalps.

Eggs and egg sac

The female wraps her eggs in a rounded, yellowish silk sac and hides it in her retreat, in a rolled leaf, a crevice in bark, or a gap in brickwork close to the web. A sac holds several hundred eggs, not the three to five that are sometimes reported — that figure appears to be a long-running copying error. A female may produce more than one sac in a good season.

Spiderlings

Spiderlings emerge and disperse on silk threads within days, feeding themselves from the start. The species usually passes the cold months as a half-grown juvenile tucked into a silk cell in a crack or under bark, then finishes growing in spring, so adults are most abundant from early summer to autumn. In mild regions some females survive the winter as adults and are found almost year-round, which is why this spider turns up in winter surveys when most orb weavers have gone.

The web

This is a nocturnal orb weaver. At dusk the spider spins a neat vertical orb, typically 15–30 cm across, in low vegetation or across a gap in a structure, and sits head-down at the hub all night. Before dawn it eats the sticky spiral, recovering the protein, and retreats into a thimble-shaped silk shelter at the end of a signal line — under a leaf, inside a rolled reed, or in a crack in stonework — where it waits out the day with one foot on the line. Rebuilding a whole orb web every evening keeps the silk fresh and sticky, and lets the spider move the web if the hunting is poor.

Where the furrow spider lives

Larinioides cornutus has a Holarctic distribution: it is found right across Europe, through Russia and temperate Asia to Japan and Korea, along the northern fringe of Africa, and across most of the United States and Canada north into Alaska. Few orb weavers occupy so much of the northern hemisphere, and it is one of the commonest orb-weaving spiders of both Britain and North America.

Almost everywhere it is tied to damp ground. Reed beds, marsh edges, canal and river banks, lake shores, wet ditches and damp meadows are the core habitat, and the spider readily uses man-made structures in the same places: bridge parapets, jetties, boat sheds, lock gates, fences, barn doorways and window frames near water. Insects emerging from the water in the evening are the reason for that preference — the web is positioned to intercept the nightly hatch. Away from water it is much less common.

Are furrow spiders venomous?

Yes, in the ordinary sense that almost all spiders are venomous: the furrow spider uses venom to immobilise midges, mosquitoes and moths caught in the orb. The venom is not medically significant to humans or pets, and there are no reports of tissue damage, systemic symptoms or serious reactions from this species. It has no relationship to the recluse spiders or the widow spiders, and its fangs are small.

Can furrow spiders bite?

A furrow spider can bite if it is handled roughly or trapped against skin — for example if one is caught inside a glove or between a hand and a fence rail. It is not an aggressive spider, and its first reaction to a disturbance is to run into its retreat or drop from the web on a dragline.

The bites that are reported feel like a small pinch or nettle sting, with a spot of redness and perhaps slight swelling that fades within a few hours. Wash the area with soap and water and use a cold pack if it is uncomfortable. Medical advice is only warranted if the redness spreads, pain increases after the first day, or there are general symptoms such as widespread hives or breathing difficulty, which would indicate an allergic response rather than venom toxicity. Do not apply heat, cut the site or attempt to suck out venom.

Ecological importance and behavior of the furrow spider

The furrow spider is a night hunter that puts its whole day's silk investment into one structure and takes it back again at dawn. Sitting at the hub, it locates prey by the tug of a struggling insect on the radial lines, rushes out, bites and wraps. Because the webs stand where flying insects emerge from water, the diet is dominated by midges, mosquitoes, mayflies, caddisflies, small moths and gnats — precisely the insects people least want around a lake or a garden pond. A dense colony along a canal bank removes very large numbers of biting flies over a summer.

Natural predators: mud dauber wasps are the most consistent enemy. Black-and-yellow mud daubers hunt orb weavers specifically, paralyse them and seal them into mud cells as food for their larvae. Birds, shrews, larger spiders and parasitoid wasps take their share too, and the daytime retreat exists largely to make the spider hard to find.

Mating: males stop feeding when they mature and go looking for females, drumming on the edge of a web to identify themselves before approaching. Courtship is careful for good reason, but unlike some orb weavers this species is not a routine cannibal, and a male may mate more than once.

Seasonal pattern: juveniles overwinter in silk cells, mature through spring and early summer, and populations peak in late summer and autumn. In warm coastal regions adults can be found in almost any month.

Relationship with humans: entirely benign. The spider is often abundant on human structures near water without anyone noticing it, because the web is gone by daylight. No control measure is needed or sensible.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The Swedish naturalist Carl Alexander Clerck described this spider in 1757, in the very first book to use consistent two-part scientific names for animals — a year before Linnaeus's tenth edition.
• "Furrow" and "foliate" both describe the same thing: the wavy-edged central band on the abdomen, which looks either like a plough furrow or like the outline of an oak leaf.
• Eating the web each morning recovers most of the protein invested in it, so the spider can rebuild every night on a modest food intake.
• Laboratory work on Larinioides cornutus has been used to study how hormones and feeding state change a spider's boldness, making this one of the standard model animals for spider behaviour research.
• Because it survives cold so well, it is one of the few orb weavers that can still be found active on mild winter nights in coastal regions.

In summary, the furrow spider is an abundant, harmless, water-loving orb weaver that most people have stood beside without ever seeing. Learn the scalloped pale band on the abdomen, look for a fresh orb at dusk near water, and check the nearby crevices for the daytime retreat.