Starbellied Orb-weaver (Acanthepeira stellata)

Physical description and identification

The starbellied orb-weaver is one of the easiest North American spiders to name once you have seen one. The abdomen is not smooth but armed with a ring of blunt, conical projections — usually ten to twelve, the largest of them at the rear — so that the outline reads as a rough, lopsided star. The body is brown, mottled with cream and darker chestnut, and the whole animal looks dry and woody rather than glossy.

Adults

• Size: females measure about 7–15 mm in body length and males 5–8 mm, so a large female is roughly the length of a grain of rice and the male about half that. Females are also far heavier-bodied.
• Colour: shades of brown from pale tan to dark chocolate, usually with a paler central band and scattered light flecks. The legs are brown with darker bands and carry stout spines.
• The spines: the tubercles are firm outgrowths of the abdomen wall, not hairs, and they hold their shape. Counting them is the quickest confirmation; ten to twelve is normal, and the rearmost pair is the most prominent.
• Head shape: the front of the carapace is drawn upward and forward into a raised projection carrying the anterior median eyes. Popular accounts describe this as “two eyes on points”, which is close but imprecise — it is the head region itself that is produced, lifting that pair of eyes above the rest. Our guide to spider eyes explains the standard araneid arrangement.
• Sexes: males are smaller, longer-legged and have less pronounced tubercles, with swollen pedipalp tips once mature.

Eggs

The female produces a rounded silk egg sac holding a few hundred small round eggs, attached to vegetation or tucked into curled leaf litter rather than hung in the web. Most sacs are made in late summer, and the young of the year appear from the following spring.

Spiderlings

Hatchlings remain together in a loose cluster for a short period after emerging, then disperse — many on wind-carried silk — and begin building small orbs of their own in low vegetation. The tubercles are present from an early instar but become proportionally more obvious with each moult.

The web

The web is a classic vertical orb, modest at roughly 15–25 cm across, spun low among grasses, goldenrod stems and shrubby herbs, often less than a metre above the ground. It is rebuilt frequently, and the spider commonly leaves the hub and waits in a retreat of curled leaves or bunched stems at the end of a signal line. That habit, plus the cryptic shape, means people usually find the web first and the spider only after a careful search. See our spider web guide for how an orb is constructed.

Where the starbellied orb-weaver lives

Acanthepeira stellata is a North American species. Its core range is the eastern and central United States, from New England and the Great Lakes south to Florida and west to the Great Plains and eastern Texas, with records extending north into southern Canada and south into Mexico. Popular sources sometimes frame the range as “Mexico to Canada”, which makes those edges sound like the centre; the spider is far more abundant in the middle of that band than at either end.

Habitat is open and herbaceous. Meadows, old fields, prairie remnants, roadside verges, marsh margins, powerline cuts, woodland clearings and unmown field corners all suit it, and the key requirement is a stand of tall grass or forbs sturdy enough to support a small orb. It is not a house spider and is only occasionally found on buildings.

Are starbellied orb-weaver spiders venomous?

Yes, in the same way as almost every spider: the starbellied orb-weaver uses venom to immobilise the insects it catches. That venom has no medical significance for humans, pets or livestock. There is no antivenom because none is required, and there are no documented cases of serious illness or tissue injury attributed to this species. It belongs to the orb-weaver family Araneidae, a group with no medically important members anywhere in North America.

Can starbellied orb-weaver spiders bite?

It can, but almost never does. This is a timid spider that responds to disturbance by dropping from the web on a dragline, folding its legs and lying still — a posture in which it passes convincingly for a burr or dried bud. Bites are recorded only after deliberate handling or when a spider is pressed against skin.

The effect is minor: a brief sting, a small red mark, occasionally slight itching for a few hours. Wash the area with soap and water and apply a cold pack if it is uncomfortable. No further treatment is needed. Seek medical advice only if redness and swelling spread well beyond the site, which would point to an allergic response rather than to the venom itself.

Ecological importance and behavior of the starbellied orb-weaver

The starbellied orb-weaver is a web-bound ambush predator of open grassland. It rebuilds or repairs its orb regularly, waits with a foot on a signal line, and rushes out when vibration tells it something has struck the silk. Prey is bitten, wrapped and either eaten at once or stored. Because the web sits low in the herb layer it intercepts a different set of insects from the higher webs of larger orb-weavers, which is part of why several araneid species can share a single meadow.

Diet: small beetles, moths, flies, leafhoppers, small wasps and other grassland insects. In hayfields and pasture margins this adds up to a genuine, unpaid contribution to pest control.

Camouflage and defence: the combination of brown mottling, a knobbly outline and complete stillness is the species' main defence. Dropped into the litter, it is effectively invisible. The tubercles probably also make the spider harder for a small bird to handle, a strategy shared with the far more colourful spiny orb-weavers.

Natural predators: birds, mud-dauber and spider wasps, ants, lizards, robber flies and larger spiders. Parasitoid wasps that lay eggs on orb-weavers take a steady share of the population, and egg sacs are attacked by parasitic flies and wasps.

Seasonal behaviour: the spiders mature through early summer, and adults are most often seen from late spring into early autumn, peaking in midsummer. Males abandon web-building on maturity and search for females, approaching cautiously along the frame threads. Adults do not survive the winter in most of the range; the species overwinters as eggs and young juveniles.

Relationship with humans: harmless and beneficial. Leaving field edges and a corner of the lawn unmown is the single most effective way to keep them, and their prey, around.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The species name stellata is Latin for “starred”, a direct reference to the ring of abdominal points.
• It was described in 1805 by Charles Athanase Walckenaer, making it one of the earliest North American spiders to receive a scientific name.
• The genus Acanthepeira was erected in 1883 by George Marx, a German-born physician who became one of the first serious students of American spiders and worked for the US Department of Agriculture.
• Sweep-netting a meadow in July usually turns up starbellied orb-weavers in numbers that surprise people, because the species is far commoner than its visibility suggests.
• The spiny shape is a case of convergent evolution — unrelated orb-weavers such as the tropical Gasteracantha arrived at armoured abdomens independently.

In summary, the starbellied orb-weaver is a small, thorny, thoroughly harmless meadow spider that has made a career out of looking like plant debris. Count the points around the abdomen and you have named it.