Fierce Orbweaver Spider (Araneus saevus)

Physical description and identification

The fierce orbweaver is a large, sombre member of Araneus, and in a genus full of orange, cream and marbled species it stands out by being almost black. The body is matt rather than glossy, the abdomen high-shouldered and lumpy, and a pale cream or white stripe runs along its upper surface. Picked out by a head torch at the hub of a web slung between spruce branches, it is an unmistakable northern forest animal.

Adults

• Size: females measure about 11–21 mm (0.43–0.83 in) in body length, males 9–14 mm (0.35–0.55 in). A large female is a substantial spider, comparable to a big garden orb weaver, and the leg span roughly doubles those figures.
• Colour: dark brown to blackish overall, with a cream or white stripe down the centre of the abdomen and dark, faintly ringed legs. The pale pattern can be reduced to a few spots, but the overall darkness is consistent.
• Distinctive features: several low humps, or tubercles, along the top of the abdomen give the spider a bumpy silhouette that breaks up its outline against bark. The forward pair, the shoulder humps typical of the genus, are the most prominent.
• Eyes: eight small eyes in two rows of four, none enlarged, with the side pairs set together on low mounds. There are no forward-facing headlight eyes, which separates it at a glance from any large hunting spider.

Eggs and egg sac

The female produces a silk egg sac in late summer or autumn and hides it in a crevice of bark, under loose scales or in a shelter of drawn-together needles rather than on the web. This is the stage that carries the species through a boreal winter: the adults die with the first hard frosts and the sac survives months of sub-zero temperatures. Our guide to where spiders go in winter explains why.

Spiderlings

The spiderlings are yellow when they emerge in spring, and they darken with each moult until the adult brown-black appears late in the season. They disperse as tiny first- and second-instar spiders by ballooning — releasing silk from an exposed twig and letting the wind carry them — which is how isolated stands of spruce are colonised.

The web

The web is a large vertical orb, strong but noticeably open: radii and spiral turns are widely spaced compared with a garden orb weaver's fine mesh, which suits a spider taking big, slow-flying forest insects rather than midges. It is built between the branches of spruce and other conifers at a range of heights, commonly one to two metres above the ground; the frequently repeated figure of 150 cm is a typical value rather than a rule. The spider is nocturnal, sitting at the hub after dark and withdrawing before dawn to a retreat in bark or curled needles, connected by a signal line. For how the frame, radii and spiral are laid down in sequence, see our guide to spider webs.

Where the fierce orbweaver lives

Araneus saevus is a Holarctic species — it occurs right across the northern forests of both hemispheres. In North America it is a spider of Canada, Alaska and the northern United States, extending south along the Appalachians and the Rockies where high ground keeps the climate cool. In Eurasia it runs through northern and central Europe and across Russia. It is not introduced on either continent; the distribution reflects the continuous band of boreal forest that once linked them.

Habitat is narrow and consistent: coniferous and mixed forest, with a strong preference for spruce. The spider needs branch structure solid enough to anchor a wide orb, bark or dense needles for a daytime retreat, and the moth and crane fly traffic of a damp northern woodland. It is a forest animal rather than a garden one, so unlike many large orb weavers it is rarely found on buildings; most encounters involve campers, foresters and hikers meeting a web across a trail at dusk.

Are fierce orbweaver spiders venomous?

Yes, in the way that almost all spiders are: the fierce orbweaver uses venom to subdue moths and flies caught in its web. It is not venomous in any sense that matters to people. No North American or European orb weaver is medically significant, no antivenom exists for any of them because none is needed, and there is no credible record of serious illness caused by this species anywhere in its range. Despite its size and its alarming name, it is unrelated to the recluse and widow spiders and carries none of their toxins.

Can fierce orbweaver spiders bite?

A spider this size can certainly break skin, but it very rarely does. The defensive sequence of an orb weaver is to shake the web violently, drop out of it on a dragline and lie still in the litter. Almost every recorded orb weaver bite involves a spider trapped against skin — grabbed bare-handed, caught in a sleeve, or pressed against a palm by someone walking into a web in the dark.

The result is a sharp prick with local redness and perhaps mild swelling, typically gone within a day. Wash the area with soap and water, apply a cold pack if it is sore, and take an ordinary painkiller if needed. Increasing pain, spreading redness or any difficulty breathing is not an effect of this venom and would suggest an allergic reaction or a secondary infection — reasons to see a doctor rather than to worry about the spider.

Ecological importance and behavior of the fierce orbweaver

This is a nocturnal sit-and-wait predator. The orb is renewed at dusk, the spider holds the hub through the night, and by daylight it has withdrawn into bark or needles with a leg on the signal line. When a moth hits the sticky spiral it reads the vibration, runs down a radius, bites and wraps the insect before carrying it back. The wide mesh lets small prey pass straight through, so the diet skews toward large, soft-bodied night fliers: crane flies, moths, caddisflies, lacewings and beetles.

Natural predators: mud dauber and spider wasps hunt orb weavers at the web, paralyse them and seal them into nest cells as living provisions. Ichneumon and other parasitoid wasps lay eggs on living spiders, and insectivorous birds take adults and egg sacs. Wandering males are the most exposed of all.

Prey-predator dynamics: in a spruce forest with few other large web-builders, a population of fierce orbweavers takes a meaningful share of the night-flying insect biomass, including moths whose caterpillars defoliate conifers. The spiders in turn feed wasps and birds.

Seasonal behaviour: the cycle is strictly annual. Spiderlings emerge in spring, grow through the summer, and mature in late summer and autumn — which is when the biggest, most photogenic females appear. Males stop building webs on maturity and travel to find females, approaching carefully along the edge of an orb; most die soon after mating. Females lay, conceal the sac and die before winter.

Relationship with humans: harmless, and mostly invisible. The species does not come into buildings or aggregate around lights the way some house-associated orb weavers do. If a web crosses a trail, duck under it; the spider rebuilds that night regardless.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The species was described in 1872 by Ludwig Carl Christian Koch, a German arachnologist — not an entomologist, as is often written. He is cited as “L. Koch” to distinguish him from his father Carl Ludwig Koch, also a prolific describer of spiders.
• Saevus means fierce, savage or cruel in Latin. Nineteenth-century arachnologists chose epithets for appearance as readily as behaviour, and a heavy, dark, humped spider struck Koch as looking the part.
• A Holarctic range like this one is a relic of the continuous northern forest that once stretched across the Bering land connection — a pattern repeated in northern beetles, birds and plants.
• The open mesh of the web is a design, not a sloppy build. Widely spaced spiral turns use less silk and catch fewer small insects, but they hold the big-bodied moths a conifer forest supplies at night.
• Overwintering as eggs is the standard northern strategy: a sac tolerates temperatures that would kill the adult outright, which is why spring brings spiderlings rather than survivors.

In summary, the fierce orbweaver is a large, dark, entirely harmless spider of the northern spruce forest. It takes moths at night from a wide, strong orb, hides in bark by day, leaves only its egg sac to face the winter, and carries a fearsome name for no better reason than its looks.