Hawaiian Garden (Argiope appensa)

Physical description and identification

The Hawaiian garden spider is one of the easiest large spiders in the Pacific to name on sight. An adult female sits in the open at the centre of her orb, head-down, legs arranged in four paired sets that form a rough X, with a bright black-and-yellow abdomen and a head region covered in dense silver hairs. Nothing else in her range combines that colour scheme with a zig-zag ribbon of white silk running through the web.

Adults

• Size: females have a body length of roughly 19–25 mm and a leg span that can reach about 6 cm. The often-quoted figure of "2 to 2.5 inches" describes the spider with her legs spread, not the body. Males are a different animal in scale: about 6–10 mm long and perhaps a twentieth of the female's mass.
• Colour — female: the carapace is black beneath a coat of silvery-white hairs. The abdomen is broad and shield-shaped, banded and blotched in yellow and black, sometimes with white or orange along the front edge. The underside is black with two pale yellow stripes. Legs are black with yellow to orange basal segments.
• Colour — male: plain light brown to tan, unbanded and easily overlooked. He usually lives on a small web attached to the edge of a female's orb.
• Distinctive features: the abdomen edge is slightly lobed rather than smooth, and the eight eyes sit in two rows with the side pairs on small mounds. In the Argiope genus the last leg pair is used to sling silk over prey, which is why an Argiope wraps a grasshopper into a parcel in seconds.

Eggs and egg sac

The female does not carry her eggs. She spins a papery, brown to tan sac shaped like a flattened urn or teardrop and fixes it to sturdy vegetation close to the web, often several hundred eggs to a sac and sometimes more than one sac in a season. The sac wall is tough and weatherproof, and the female guards it while she is still alive.

Spiderlings

Spiderlings hatch inside the sac, moult once, and stay there until conditions suit them. They leave as a crowd, disperse by ballooning on silk threads, and build miniature orbs in low vegetation. Juveniles often decorate the hub with a solid white disc rather than the adult's zig-zag band, so a small spider in a dense-centred web is usually a young Argiope.

The web

The web is a classic vertical orb, up to about 60 cm across, with an open hub and a strong framework anchored to shrubs, fence posts, banana leaves or the gap between two trees. Its signature is the stabilimentum: a band of thick white silk, usually a vertical zig-zag above and below the hub, occasionally arranged as a cross. Its purpose is still debated — proposed explanations include advertising the web to birds so they do not blunder through it, attracting insects that respond to ultraviolet reflectance, breaking up the spider's outline, and stiffening the hub. Evidence supports more than one of these, and none of them explains every case. What is clear is that webs are repaired or rebuilt frequently, and that our page on spider webs covers the construction sequence in detail.

Where the Hawaiian garden spider lives

Despite the name, Argiope appensa is not originally Hawaiian. Its natural range runs through the western Pacific and Indo-Malayan islands — Taiwan, Indonesia, New Guinea, Guam and the Mariana Islands and neighbouring archipelagos. It became established in Hawaii after arriving with human traffic and is now abundant on the main islands, which is where the common name comes from.

It is a spider of sunlit gaps rather than deep forest or bare ground: garden hedges, roadside shrubs, banana and ti plantings, forest edges, coastal scrub and the margins of trails, anywhere with anchor points a metre or two apart and a steady supply of flying insects. On some Pacific islands it is one of the most conspicuous animals in the landscape, with webs strung every few metres along a path.

Are Hawaiian garden spiders venomous?

Yes, in the ordinary sense that it uses venom to kill the insects it catches. It is not dangerous to people. Argiope venom is tuned to insects, and no member of the orb weaver family anywhere in the world causes medically significant envenomation. There is no tissue damage, no systemic toxicity and no antivenom, because none is needed. The spider is also not aggressive: cornered on a web, its first move is to drop to the ground on a dragline or to shake the orb violently to blur its own outline.

Can Hawaiian garden spiders bite?

A female can bite if she is grabbed, pinned or pressed against skin — for example when someone pushes through a web without seeing it and traps her between clothing and body. Bites are uncommon and mild: a sharp pinch at the moment of the bite, some local redness, and occasionally slight swelling or itching that settles within a day. Many reports compare it to a bee sting, and the fangs of a large female are long enough to break skin cleanly.

Ecological importance and behaviour of the Hawaiian garden spider

This is a daytime hunter. The female spends the light hours at the hub with her legs on the radii, feeling for the tug of an insect, then rushes out, throws a sheet of silk over the prey with her hind legs and bites through the wrapping. Grasshoppers, katydids, flies, bees, wasps, moths and beetles all appear in the diet, and large prey is stored in the web and eaten over hours.

Natural predators: birds, lizards, and mud-dauber and spider wasps that paralyse orb weavers to stock their nests. Argiope webs also attract kleptoparasitic dewdrop spiders, which live along the frame lines and steal small wrapped prey.

An accidental experiment on Guam: after the introduced brown tree snake eliminated most of Guam's forest birds, spider densities on the island were found to be many times higher than on neighbouring islands that still had birds, with Argiope appensa among the most visible beneficiaries. It is one of the clearest field demonstrations that insectivorous birds hold spider populations down.

Mating: the small male builds at the edge of the female's web and waits, often for her final moult, when her fangs are soft. Mating is brief and dangerous; in this genus the male's palp frequently breaks off inside the female and acts as a plug against rivals, and the male may be eaten. Females mature toward the end of the wet season and, in the warm tropical parts of the range, adults can be found almost year-round.

Relationship with humans: harmless and useful. A garden with several of these webs has fewer flies and leaf-eating insects, and the spider will not enter houses. If a web is in a doorway, cut the frame lines at night and the spider will simply rebuild elsewhere.

Similar spiders and how to tell them apart

Quick facts

Did you know?

• The genus name Argiope comes from a figure in Greek mythology and has been in use for these spiders since the early nineteenth century; the species was described in 1841 by the French naturalist Charles Walckenaer.
• The nature writer David Quammen describes meeting these spiders in enormous numbers on Guam in The Song of the Dodo — an observation that turned out to be an early clue to the island's missing birds.
• Spiderlings decorate their small webs with a solid white disc, and the decoration changes to the adult zig-zag as the spider matures.
• Females sometimes eat and recycle the whole orb before spinning a new one, digesting the old silk proteins.
• The spider's habit of shaking the web when disturbed is a defence: a vibrating orb makes the outline of the spider impossible for a bird to fix on.
• In Hawaii the species is sometimes called a banana spider locally, a name applied to so many unrelated spiders worldwide that it is worth ignoring.

In summary, the Hawaiian garden spider is a large, showy, entirely harmless orb weaver that earns its keep in a garden. Learn the silver head, the black-and-yellow abdomen and the zig-zag ribbon in the web, and you will recognise it anywhere in the Pacific.