Arrowhead (Verrucosa arenata)

Physical description and identification

The arrowhead spider is a small, distinctive member of the orb weaver family and the best-known species in the genus Verrucosa. It is far more often noticed than most spiders its size, because the pale triangle on its back stands out against dark woodland foliage and because of where it sits in its web. Nearly all orb weavers wait head-down at the hub; the arrowhead spider waits head-up, with the broad front edge of the triangle pointing skyward.

Adults

• Size: females are 6–9 mm in body length — about a quarter of an inch — and males are smaller, around 4 mm and much slimmer.
• Colour and marking: the carapace and legs are reddish brown to chestnut. The upper surface of the abdomen carries a single large triangle, broad at the front and tapering to a point at the rear, coloured white, cream, pale yellow or, in some individuals, a soft pink. The sides and underside are brown, sometimes with fine pale flecks.
• Shape: the abdomen has low angular shoulders and small tubercles at the front corners — the genus name Verrucosa means “warty” and refers to these bumps. They are not horns or spines, and they are not used as weapons.
• Males: dull brown, without the bright triangle or with only a trace of it, and easy to mistake for a different species altogether.
• Eyes: eight small eyes in two rows. Sight is poor and the spider locates prey by feeling the tension in the radial threads.

Eggs and egg sac

Females mate in late summer and produce small, rounded egg sacs of pale silk, attached to a leaf, a twig fork or a stem near the web and often hidden in a curled leaf. Each holds a few dozen to a couple of hundred eggs. The sac is left unattended; the female does not survive the winter in the northern part of the range.

Spiderlings

Spiderlings emerge in spring, disperse quickly on silk threads and begin spinning tiny orbs in low vegetation within days. Young spiders are pale and the triangle develops gradually as they grow through successive molts. Adults appear from late spring onwards and are most obvious from midsummer into autumn.

The web

The arrowhead spider builds a classic flat orb, small by family standards at roughly 15–30 cm across, strung between shrubs, saplings, low branches and tall herbs. Webs are usually built in shaded woodland, along trail edges and in damp thickets, and very often at about eye level — hikers walk into them constantly. The orb is frequently tilted rather than perfectly vertical, and the spider sits at the hub with a free space in the centre.

Like most orb weavers in the family it maintains the web daily, taking down the damaged capture spiral and replacing it, usually in the early morning, while retaining the heavier frame lines. The species does not add a zigzag or cross-shaped silk decoration, which immediately separates it from the garden spiders. For how these different webs are built, see our guide to spider webs.

Where the arrowhead spider lives

Verrucosa arenata is a New World species with a wide range. In North America it occurs across the east, from southern Canada and New England south to Florida and west to Texas and the eastern Great Plains. It continues through Mexico and Central America into South America, and is also recorded from the Greater Antilles.

It is a spider of shaded, humid, structurally complex vegetation: deciduous and mixed woodland, forest edges, trail corridors, wooded stream banks, marsh margins, overgrown thickets and shrubby gardens that back onto woodland. It needs shrub-height vegetation with gaps to bridge, so closely mown gardens and open grassland rarely hold it. Numbers build through the summer and peak in late summer and early autumn.

Are arrowhead spiders venomous?

Yes, in the way that almost every spider is: it produces venom and uses it on the insects caught in its web. It is not medically significant to humans or pets. The fangs of a 6 mm spider are short, the venom is adapted to insect physiology, and there are no reports of tissue damage or systemic illness from this species. It is unrelated to the recluse and widow spiders responsible for medically important bites in the Americas.

Can arrowhead spiders bite?

In principle yes, but records are close to non-existent. An arrowhead spider that feels its web shaken will normally drop out of it on a dragline and hang motionless in the leaf litter until the disturbance passes. To be bitten you would have to close a hand around the spider itself — for example after walking face-first into a web and brushing it off blindly.

Any bite would amount to a faint pinprick with slight redness, settling within a few hours and leaving nothing behind. Wash the spot and use a cold pack if it is sore. The only reasons to seek medical advice are spreading redness or swelling over the following days, which suggests a skin infection, or symptoms of a general allergic reaction. Do not cut, suck or burn a spider bite.

Ecological importance and behavior of the arrowhead spider

This is a small sit-and-wait predator that stays in its web through the day, which is unusual — many orb weavers of this size hide at the edge and come out at dusk. Prey is small flying insects: gnats, midges, fungus gnats, small flies, leafhoppers, mayflies, tiny moths and parasitic wasps. It cannot handle large or heavily armoured insects and takes nothing like the frogs occasionally attributed to it; a spider this size is simply not equipped for vertebrate prey.

Defence: the abdominal bumps are not weapons. The real defences are dropping from the web on a dragline, staying motionless, and the colour pattern itself. A bright triangle surrounded by brown breaks up the spider's outline in dappled woodland light and makes it hard to read as a spider-shaped object — a form of disruptive camouflage. There is no evidence that the marking mimics a flower or attracts pollinators, a claim that is often repeated but has never been demonstrated.

Why head-up? The reversed posture is a real and consistent trait of the genus, not an occasional habit. Orb weavers that hang head-down rely on gravity for a fast drop onto prey below the hub; sitting head-up suits a small spider that builds a tilted web and runs upward. It also means the conspicuous triangle always faces the same way, which fits the camouflage explanation.

Predators: mud-dauber and spider-hunting wasps, birds, and larger spiders including other orb weavers. Parasitoid wasps attack both the spiders and their egg sacs.

Season and lifespan: the cycle is annual in the north — spiderlings in spring, adults through summer, egg sacs in late summer and autumn, adults gone by frost. Females live longer than males, which die within weeks of maturing. In the tropical part of the range adults can be found year-round.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The genus name Verrucosa comes from the Latin for “warty”, after the small bumps on the front corners of the abdomen; arenata derives from arena, “sand”, a reference to the pale sandy colour of the triangle.
• Sitting head-up in the web is rare enough among orb weavers that it alone can identify the genus, even when the triangle is faded.
• The colour of the triangle varies between individuals in the same wood — white, cream, yellow and pink forms can all be found within a few metres of each other.
• Males look so different from females, being plain brown and much smaller, that early naturalists described some of them as separate species.
• Because the webs are built at head height across woodland trails, this is one of the spiders most often carried home on a hiker's hat.

In summary, the arrowhead spider is a harmless woodland orb weaver with two features that give it away instantly: a pale triangle pointing backwards down the abdomen, and a spider sitting the wrong way up in the middle of its web.