Red-femured Spotted Orbweaver Spider (Neoscona domiciliorum)

Physical description and identification

The red-femured spotted orbweaver is a heavy-bodied, strongly patterned araneid, and easier to name than most of its relatives because the leg colour alone settles it. Every leg has a bright red or orange-red femur — the thick first segment closest to the body — while the rest is banded black and grey. No other southeastern orb weaver combines that with a dark, cross-marked abdomen.

Adults

• Size: females run about 7–16 mm in body length, males about 6–9 mm and noticeably slimmer. A well-fed autumn female is a substantial spider, roughly the size of an acorn.
• Abdomen: the upper surface is dark, almost black, overlaid with bright yellowish-white markings: a pale transverse band across the shoulders and two flanking stripes that together read as a rough cross or cruciform. The underside is reddish brown with four crisp white spots arranged in a square — the "spotted" in the common name, and a reliable check when the spider is hanging upside down at the hub.
• Legs: red femora, then black and grey banding. The pattern is strongest in adult females; young spiders can look duller and the red may be closer to orange.
• Other features: like other Neoscona the abdomen carries a shallow groove down the midline, and females are dusted with sparse short grey hairs. The carapace is dark with a pale central stripe.
• Sexes: mature males have swollen pedipalps and longer legs, build little or no web of their own, and wander in search of females in late summer.

Eggs and egg sac

Mating takes place in late summer and early autumn. The female wraps several hundred eggs in a rounded sac of pale silk and hides it in a rolled leaf, a crack in bark, a soffit or a window frame near her web. She dies within a few weeks of laying. The eggs, and the spiderlings that hatch inside the sac, pass the whole winter there.

Spiderlings

The young emerge in spring, disperse by ballooning on threads of silk, and immediately begin building tiny, neat orbs. They grow through spring and summer, and it is only in August that they become large enough for people to start noticing the webs. The species completes one generation a year.

The web

The web is a large vertical orb, reaching about 50 cm across in a mature female, built in the classic wheel form with long frame lines that run out to shrubs, railings, gutters or all the way to the ground. Inside the central hub there are only one or two threads rather than the dense mat of silk some orb weavers lay down, and there is never a stabilimentum.

It is a night web. The female spins it at dusk, sits in the hub through the dark hours and takes it down towards dawn, eating the silk to recycle the protein. By day she waits in a retreat of curled leaves at the end of a signal line, one leg on the thread so any struggle in the web is felt at once. A female preparing to lay eggs often stops rebuilding for a few nights, saving the material the sac will need. Our guide to spider webs explains how the radials and sticky spiral go up in under an hour.

Where the red-femured spotted orbweaver lives

Neoscona domiciliorum is a spider of the eastern United States, and overwhelmingly of the Southeast. It is common from South Carolina, Georgia and Florida west along the Gulf to Louisiana and eastern Texas, and it thins out northward, reaching Massachusetts on the coast and Indiana and Missouri inland. Older accounts that list only Indiana, Massachusetts and Texas are simply quoting the corners of the range; the centre of abundance is the humid Southeast.

Its preferred habitat is woodland with hardwood trees, and especially the edges of that woodland: clearings, trail sides, stream banks and the boundary between forest and garden. It is equally at home on buildings, which is where the species name comes from. Porches, eaves, shutters, carports, fence posts and outdoor light fittings all provide the solid anchor points a 50 cm web needs, and a porch light provides the insects. It is an outdoor spider, however, and unlike a true house spider it does not breed indoors.

Are red-femured spotted orbweaver spiders venomous?

Yes, in the ordinary sense that it uses venom to subdue insects caught in the web. That venom is not medically significant to people, pets or livestock. Neoscona spiders have no tissue-damaging enzymes of the kind found in recluse spiders and none of the neurotoxins that make widow bites a medical emergency, and no serious envenomation by this species has ever been documented.

Can red-femured spotted orbweaver spiders bite?

It can, but only under pressure. This is a large, conspicuous spider that a homeowner sometimes brushes off a doorframe with a bare hand, and a spider squeezed against skin will defend itself. Left alone it does the opposite: at the first heavy vibration it either drops out of the web on a dragline or retreats into its leaf shelter.

A bite is usually compared to a bee sting — a sharp pinch, a red mark, mild swelling and itching that settles within a day. Wash the site with soap and water, use a cold pack and take a simple painkiller if needed. Get medical advice only if the redness spreads over following days, if pain increases rather than fades, or if you develop hives, wheezing or dizziness; those mean infection or allergy, not the venom. Never apply heat, cutting or suction.

Ecological importance and behaviour

The red-femured spotted orbweaver is a nocturnal ambush predator that relies entirely on the web. Hanging head-down in the hub, it detects prey through the radial threads, rushes out, and either bites small insects at once or wraps larger ones in bands of silk before biting. Prey is often cut from the web and carried back to the hub to be eaten.

Diet: moths, midges, mosquitoes, craneflies, beetles, lacewings, flying ants and other night-flying insects. Webs built near porch lights and security lamps intercept an unusually rich stream of prey, which is why spiders in those positions grow so large by September.

Natural predators: mud-dauber and spider wasps paralyse orb weavers to stock their nest cells, wrens and chickadees take them from the web, and lizards, mantids and larger spiders prey on them too. Parasitoid wasps lay eggs on the abdomen; the larva feeds externally and eventually kills the spider.

Seasonal rhythm: spiderlings hatch in spring, mature in mid to late summer, and the population peaks from August into October. Males wander and die after mating; females survive until the first hard frosts, by which time the egg sacs are already hidden away.

Relationship with people: harmless and useful. A single porch-corner female removes thousands of mosquitoes and moths over a season, and where a web is in the way, brushing it down is enough — the spider rebuilds a little further off.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• Described in 1847 by Nicholas Marcellus Hentz, the French-born American naturalist who wrote the first serious treatment of the spiders of the United States.
• Domiciliorum is Latin for "of dwellings" — Hentz named it for its habit of building on the walls and porches of houses.
• Rebuilding a 50 cm orb every night costs a great deal of protein, so the spider eats the old web before dawn and recycles the silk proteins into the next one.
• The four white spots on the reddish underside are the quickest field check of all, because an orb weaver at the hub is normally seen from below.
• It belongs to a genus of more than 120 species worldwide; see our overview of the Neoscona orb weavers.

In summary, the red-femured spotted orbweaver is one of the most recognisable and most useful of the southeastern orb weavers: red-legged, cross-marked, harmless to people, and quietly clearing the night air of mosquitoes from a porch corner every evening between August and October.