Giant Lichen Orb Weaver (Araneus bicentenarius)

Physical description and identification

The giant lichen orb weaver is a heavy, broad-bodied member of the genus Araneus, and few orb weavers in the eastern United States match its bulk. What makes it hard to find is camouflage rather than rarity: the grey, green and cream mottling on its abdomen copies the crustose lichens on oak, pine and hemlock trunks.

Adults

• Size: mature females have a body length of roughly 12–25 mm and a leg span that comfortably covers the palm of a hand. Males are much smaller and narrower, about 8–12 mm, with proportionally longer legs.
• Color: the abdomen is pale grey-green to greenish white, marbled with darker grey, olive and reddish-brown blotches that form a broad, scalloped folium down the back. The carapace is grey with a darker central stripe, and the legs are strongly banded — reddish or orange near the base, ringed black and grey toward the tips. Colour intensity varies a great deal between individuals.
• Eyes: eight eyes in the typical araneid arrangement, a central square of four with a pair set well out to each side. Vision is poor and the spider reads its world almost entirely through vibration.
• Distinctive features: two low, rounded humps sit on the shoulders of the abdomen, as in several relatives in Araneus, and dense short hairs give the body a frosted, lichen-like texture. Males have swollen pedipalps and a much slimmer abdomen.

Eggs and egg sac

Mating takes place in late summer and early autumn. The female then builds a flattened, papery sac of pale yellowish silk holding several hundred eggs, tucked into a bark crevice, under loose bark or in a sheltered corner of a building near woodland rather than hung in the open web. The sac is the overwintering stage: the female dies with the first hard frosts and never sees her offspring.

Spiderlings

The young emerge in spring, pale and translucent, with only faint traces of the adult marbling. They cluster briefly, then disperse, many of them by ballooning on a thread of silk carried by rising air. Growth is slow and each stage ends in a molt, so adult size is not reached until late in the single season — which is why almost every large individual people photograph turns up between August and October.

The web

The species builds a classic vertical orb, and it builds it big. The sticky capture spiral is usually 30–60 cm across in a mature female, but the framework that carries it is what people remember: bridge and anchor lines can be strung two to three metres between trunks, across a forest track or from a porch roof to a shrub, so the whole structure spans the best part of 2.5 m. For how an orb is laid out, see our explainer on spider webs.

Unlike the yellow garden spider, which hangs head-down at the hub in daylight, this species retreats at dawn into a small silk shelter at the rim of the web — under a curled leaf, a bark flap or a piece of siding — keeping one leg on a signal line that runs back to the hub. At night it does sit at the centre, which is why the same web can look abandoned by day and occupied by torchlight.

Where the giant lichen orb weaver lives

Araneus bicentenarius is a North American endemic. Its range runs from the Maritime provinces and southern Ontario and Quebec south through New England and the Appalachians to Florida, and west to the Mississippi valley and eastern Texas. It is patchily distributed everywhere: locally common in the right woodland, absent from apparently similar woods a few kilometres away.

The habitat is mature, shaded forest with old trees, especially stands carrying a good growth of lichen and moss on the trunks: hemlock ravines, mixed oak-hickory woods, riverside timber and swamp edges. Because the spider needs wide gaps to sling its bridge lines across, it favours structural edges such as a trail, a stream corridor or a gap left by a fallen tree. It also uses human structures beside woodland, and is regularly reported from the beams of covered bridges, barn eaves, porch corners and the undersides of decks.

Are giant lichen orb weaver spiders venomous?

Yes — like nearly every spider it produces venom and uses it to immobilise the insects it catches, and that venom has no medical significance for people or pets. Orb weavers as a group, including every member of Araneidae, lack the tissue-destroying enzymes of the recluses and the potent neurotoxins of the widows, and none appear on any list of medically important spiders. No serious illness has been documented from a bite by this species.

Its real defence is concealment. A disturbed spider drops out of the web on a dragline or shuttles to its retreat and freezes against the bark, where the lichen pattern does the rest of the work.

Can giant lichen orb weaver spiders bite?

It can, but it very seldom does. A spider that is picked up, squeezed or trapped against skin may bite in self-defence; one met in its web will not. Reported bites produce a brief sharp pinch, a small red mark and perhaps a little itching or local swelling that fades within a day. The large fangs of a mature female break the skin more easily than those of a small orb weaver, so the pin-prick is more noticeable, but the reaction stays local.

Wash the area with soap and water, apply a cold pack and leave it alone. Seek medical advice only if redness spreads, a fever develops, or you show signs of an allergic reaction — those point to infection or sensitivity rather than the venom.

Ecological importance and behavior of the giant lichen orb weaver

This is a nocturnal ambush predator on the wing traffic of the forest. Moths make up much of the diet, along with beetles, craneflies, lacewings, caddisflies and any fly or wasp unlucky enough to cross the gap at night. Prey is wrapped in silk and either eaten at the hub or carried to the retreat.

Natural predators: birds take spiders resting on bark by day, and mud-dauber wasps hunt orb weavers specifically, paralysing them and sealing them into mud cells for their larvae. Ichneumon wasps, predatory bugs and larger spiders take their share; ants and parasitoid flies raid egg sacs. Our overview of what eats spiders sets out the wider picture.

Prey-predator dynamics: because its orb hangs high and wide in gaps other orb weavers cannot span, it intercepts a different slice of the insect community than the low webs of spotted orb weavers or the daytime webs of barn spiders, so several species share the same woodland without competing directly.

Seasonal behavior: the life cycle is annual — hatch in spring, grow through summer, mature in late summer, mate in early autumn, die with the frosts. Males stop building webs once mature and wander in search of females, plucking the threads of a female's web in a distinctive rhythm to announce themselves.

Relationship with humans: harmless and almost entirely beneficial. A web across a doorway can simply be knocked down; the spider rebuilds nearby the next night. No control measures are warranted.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The American arachnologist Henry Christopher McCook described the species in 1888; the name bicentenarius marks a two-hundredth anniversary, from his work in Philadelphia around the bicentenary of William Penn's arrival.
• The camouflage is a true resemblance to lichen, not a general grey: pale patches match the crusty grey-green thalli on hardwood bark, and the spider rests with its legs drawn tight against the body to erase its outline.
• Reports of eight-foot webs are not wrong, but they describe the whole framework. The sticky spiral that actually catches insects is a fraction of that; the rest is scaffolding.
• Being nocturnal and cryptic, the species is badly under-recorded; many county records exist only because someone walked into a web after dark and went looking for its owner.

In summary, the giant lichen orb weaver is a big, harmless, beautifully camouflaged forest spider that works at night. Finding one means finding woodland old enough to grow lichen on its trees, and the spider is a good sign rather than a problem.