Wasp (Argiope Bruennichi)

Physical description and identification

The wasp spider is one of the Argiope garden spiders, a genus of large, boldly marked orb weavers found on every warm continent. An adult female is unmistakable; the male is so small and drab that most people never notice him at all.

Adults

• Size: females measure about 14–17 mm in body length — a fingernail's length — and look bigger because of the broad abdomen. Males are only 4–5 mm, roughly a quarter of the female's length and a tiny fraction of her weight.
• Colour: the female's abdomen is broad and oval, crossed by about a dozen bands of bright yellow, black and silvery white that run right around the body. The carapace is covered in dense silver-grey hairs, and the legs are pale with dark bands. Males are plain pale brown with faint markings and no yellow.
• Eyes: eight eyes in two rows of four, the lateral pairs set well apart on the sides of the head. None are enlarged, so the spider hunts entirely by feeling vibration in the silk.
• Distinctive features: the combination of a wide, hornet-striped abdomen and a low orb web with a zigzag silk ribbon identifies this species instantly. The spider hangs head-down at the hub with its legs held in four pairs, forming an X.

Eggs and egg sac

After mating in late summer the female builds a remarkable egg sac: a brown, flask- or urn-shaped purse of papery silk about 20–25 mm tall, slung between grass stems a short distance from the web and anchored with guy lines. It holds roughly 200 to 400 eggs. She guards it for the few weeks she has left and dies in autumn, leaving the sac to overwinter on its own.

Spiderlings

The eggs hatch inside the sac in autumn and the spiderlings stay there all winter, living on their yolk reserves. They break out in spring, climb to the tips of grass and disperse by ballooning on silk threads, which is how the species colonises new ground so quickly. Juveniles grow through the summer and mature in July and August, so the whole life cycle takes one year.

The web

The web is a neat vertical orb, usually 20–50 cm across, built low in tall grass with the hub only a foot or two above the ground — exactly where grasshoppers jump. Fresh webs are spun in the low light of dawn or dusk and renewed every day or two. Its signature is the stabilimentum: a dense zigzag ribbon of white silk running above and below the hub. Its purpose is still argued over. The main hypotheses are that it advertises the web to birds so they do not fly through it, that it reflects ultraviolet light in a way that attracts insects, and that it breaks up the spider's outline; the evidence supports more than one of these, so treat any single confident explanation with caution. For the wider picture, see our guide to spider webs.

Where the wasp spider lives

Argiope bruennichi was originally a spider of the Mediterranean and central Europe — it has long been common in France, Italy and Spain — but its range has expanded dramatically over the last century as summers have warmed. It now reaches Scandinavia and the Baltic states, and it is established across much of Britain, where it was first recorded on the south coast in the 1920s and remained a rarity until it spread widely from the 1990s onwards. Beyond Europe it occurs in North Africa, the Azores, Turkey and the Caucasus, and eastwards through Central Asia to China, Korea and Japan.

The habitat is consistent everywhere: sunny, undisturbed rough grassland. Meadows, heathland, road verges, field margins, dune slacks, scrubby wasteland and the long grass at the edge of gardens all suit it, provided the vegetation is tall enough to anchor a web and open enough to catch the sun. It avoids dense woodland, mown lawns and buildings, so unlike many European orb weavers it is almost never found indoors.

Are wasp spiders venomous?

Yes, like nearly all spiders — the venom is what allows a 15 mm spider to subdue a grasshopper several times its own weight. It is not medically significant to people or pets. There is no tissue damage, no systemic illness and no recorded serious reaction from a wasp spider bite anywhere in its range.

Can wasp spiders bite?

A wasp spider can bite, but almost never does. Bites happen only when the spider is held, squeezed or trapped against skin — picking a female off her web by hand is the usual way it goes wrong. Her fangs are small and the puncture is often not even visible.

Where bites have been reported, the effect is a brief sting comparable to a nettle or a small bee sting, with a spot of redness and sometimes mild local swelling that clears within a few hours to a day. Wash the area with soap and water and apply a cold pack if it is sore. Seek medical advice only if the redness spreads, pain worsens after the first day, or there are signs of a general allergic reaction such as widespread hives or breathing difficulty. The simplest precaution is not to handle the spider: look, photograph, and leave her in the web.

Ecological importance and behavior of the wasp spider

The wasp spider is a daytime sit-and-wait predator that rarely leaves its web. It specialises in orthopterans — grasshoppers, crickets and bush-crickets — far more than most orb weavers do, and also takes bees, hoverflies, flies and beetles. Large prey is wrapped in a broad sheet of silk before it is bitten, which is why a female's web often carries several neat white parcels. In good grassland a population makes a measurable dent in grasshopper numbers.

Mating and cannibalism: males mature earlier than females and wait at the edge of a female's web for her final molt, when her fangs are still soft. Copulation lasts only seconds and a majority of males are caught and eaten during or just after it. The male's response is a form of insurance: he snaps off the tip of his pedipalp inside the female's genital opening, leaving a plug that makes it harder for a rival to mate with her.

Natural predators: birds, lizards, shrews and hunting wasps take adults, and the conspicuous egg sac is heavily attacked by parasitoid wasps and flies, and by ichneumonids whose larvae eat the eggs from inside. Many sacs fail entirely.

Seasonal pattern: spiderlings appear in spring, females are adult and most visible from late July to October, and the whole adult generation dies with the first hard frosts. Webs are easiest to find in late summer, when the females are largest and the grass is still standing.

Relationship with humans: harmless and useful. The species is a good indicator of unimproved, unsprayed grassland, and its arrival in a meadow is usually a sign that the habitat is in decent condition. It does not enter houses and needs no control of any kind.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The species was described in 1772 by the Italian naturalist Giovanni Antonio Scopoli and named after the Danish zoologist Morten Thrane Brünnich.
• Its northward march across Europe is one of the best-documented range expansions of any invertebrate, and genetic work shows the spread involved mixing between long-separated populations, which may have helped the spiders tolerate colder summers.
• A subspecies, Argiope bruennichi nigrofasciata, has been described from parts of the Mediterranean; most other named forms are simply colour variants.
• Grasshoppers are so central to its diet that the density of wasp spider webs in a meadow tends to track the density of grasshoppers there.
• Young wasp spiders build a circular disc of stabilimentum silk at the hub instead of the adult zigzag, so a juvenile web can look like a different species' work.

In summary, the wasp spider is a harmless grassland specialist wearing a hornet's warning colours. Find a low orb web with a white zigzag through the middle in late summer and you have found one — no treatment needed, and nothing to fear.