Triangular Spider Identification Australia: Arkys Guide

About the Triangular spider

Triangular spider is a useful common name for members of the genus Arkys, a group of small Australian ambush spiders in the family Arkyidae. A likely identification comes from a combination of features: a body around 6–9 mm long, a triangular or heart-shaped abdomen, two enlarged spined front leg pairs held forward, much shorter rear legs, and a leaf or shrub setting without an orb web. Bright red, orange, yellow, black and white patterns occur, but some Arkys look more like bird droppings, so colour alone is not a dependable test. This is a genus-level guide: a clear photograph can support Arkys, but identifying an individual to species may require locality, sex and microscopic characters.

How to identify an Arkys triangular spider

Start with structure rather than pattern. From above, many Arkys have a pointed triangular or broad heart-shaped abdomen attached to a compact front body. The first and second leg pairs are conspicuously larger than the rear pairs, armed with visible spines and often swept forward in a crab-like prey-waiting pose; the third and fourth pairs are much shorter. The spider is small—Australian Museum gives a body length of about 6–9 mm—so a 5-cent coin comparison that includes the outstretched legs can exaggerate its size. The usual context is also informative: one animal sitting still on a leaf, under a leaf or among shrub foliage, with no circular orb or messy prey-catching web. Photograph the whole animal before trying for a macro image; dorsal shape, side-on leg proportions and the surrounding plant are all useful evidence.

Clues that are not enough on their own

• A red, orange or yellow body: several unrelated foliage spiders share these colours.
• A triangular silhouette in one photograph: camera angle, a folded abdomen or partly hidden legs can change the outline.
• A crab-like pose by itself: true crab spiders also hold enlarged front legs sideways or forward.
• A bird-dropping pattern by itself: some Arkys mimic droppings, but several orb-weaver groups do too.
• Finding it in a named state: the genus is widespread, while individual Arkys species have narrower and incompletely documented ranges.

Colour, sex and life-stage variation

The bright studded form in the main photograph is Arkys walckenaeri, one species example rather than a colour template for the whole genus. Australian Museum notes red, yellow, orange, black and white forms, and also warns that not every Arkys is brightly coloured or sharply triangular. Some species are dark, knobbly or convincingly bird-dropping-like; the documented black melanic form of Arkys curtulus is a striking counterexample to the hero image. Males and females can have similar colours, although males tend to be slightly smaller with a narrower abdomen. Juveniles may lack the proportions or finished pattern of adults. The historic spelling Arcys appears in older literature, including the 1982 behaviour paper, but Arkys is the accepted genus spelling. Because visible variation overlaps among species, do not assign a species name from a single top-view photo unless diagnostic evidence and locality support it.

Behaviour, web and retreat

Triangular spiders are sit-and-wait hunters rather than conventional orb-weavers. By day an Arkys may remain motionless on or beneath a leaf with its two long front leg pairs spread to seize passing insects, especially flies. It does not build a sticky capture web. Australian Museum reports that individuals may move at night on a silk line or hang from a few lines, while Barbara York Main's study of the south-western species then called Arcys nitidiceps described a non-sticky single-line suspension web and recorded flies plus one moth as prey. Those safety lines are not evidence of an orb web. Silk is also used for egg sacs and attachment to leaves; females may make a small egg sac in late summer. This ambush behaviour and the exaggerated front legs are often more useful than the abdomen colour in a field photograph.

Australian distribution

Arkys is an Australasian genus, and Australian Museum describes triangular spiders as occurring throughout Australia, particularly along the east coast. They are associated with trees and shrubs in eucalypt forest, woodland, garden foliage and regenerating vegetation, and are most prevalent in summer. Atlas of Living Australia and the Australian Faunal Directory confirm Arkys as an accepted Australian genus in Arkyidae and list multiple Australian species, but genus-level presence does not mean every species occurs in every state or territory. Online occurrence coverage and converted state lists can also be incomplete. Treat location as a supporting filter: retain the date, suburb or broad locality and habitat with your photographs, then check a species-level distribution only after the structural features support that species.

What to do if you find one

Leave the spider on its leaf if practical; it is a small predator of insects and the Australian Museum describes the group as harmless to humans. Do not handle it simply to obtain a closer view. For an identification request, take a directly overhead photo, a side view showing the spines and relative leg lengths, a wider habitat photo, and one frame with a ruler or coin beside—not under—the spider. Note whether a capture web was genuinely present. If moving it is necessary, guide it into a container with paper rather than using bare fingers, then release it into sheltered foliage nearby. If a bite is suspected, ordinary wound care and symptom monitoring are appropriate; the health advice above is for symptoms, not evidence that Arkys is medically significant.

Compare with similar spiders

Use body shape, web or retreat, location and behaviour together before settling on a likely match.

• Flower spider / crab spider — Shares enlarged front legs and a foliage ambush posture, but a true crab spider usually lacks the characteristic Arkys combination of a sharply angular abdomen, extremely short rear legs and studded Arkys patterning.
• Trapezoid crab spider — Can be angular and sit on foliage, but compare its more crab-spider-like body, rear-leg proportions and abdominal outline rather than relying on the common name.
• Bird-dropping spider — May be lumpy, black-and-white and bird-dropping-like, but many bird-dropping orb-weavers have different leg proportions and web-related behaviour; some Arkys also mimic droppings, so this comparison may remain at genus level.
• Jewel spider — Has a hard, often spined or shield-like abdomen and normally occupies an orb web; an Arkys is an ambush hunter with enlarged front legs and no prey-catching orb.

Sources for this profile

These accessible authoritative sources support the identification and bite-safety context on this page.

• Australian Museum: Triangular Spiders, Arkys spp.
• Australian Faunal Directory: Arkys
• Atlas of Living Australia: Arkys
• World Spider Catalog: Arkys
• Main 1982: Reduced web, behaviour and prey of Arcys nitidiceps
• healthdirect: Spider bites

Profile review

Published by Spider Identifier Australia. Last factual review: 10 August 2026.