Triangular Spiders

Introduction

Triangular spiders are brightly coloured, distinctive spiders. Their unusually shaped and brilliantly coloured and patterned abdomens make them stand out from the crowd.

Identification

As their common name suggests they have a very distinctive triangular or heart-shaped abdomen that is often brightly coloured and patterned in a combination of red, yellow, orange, black or white. Their first two pairs of legs are enlarged, covered in spines and held curving forward to catch prey. The last two pairs of legs are much shorter in comparison.

Males and females are very similar in colour, but males usually have a narrower abdomen than their respective females and slightly smaller size.

Triangular spiders have been placed in several different families since their original description, including Araneidae, Mimetidae and Tetragnathidae. Since 2017 they have been placed in the family Arkyidae along with one other small genus. Arkys was sometimes previously spelled with a ‘c’ instead of a ‘k’ but this spelling is no longer used.

Not all species in the genus Arkys are the brightly coloured triangular spiders. Some other species in this genus mimic bird droppings in size, colour and shape.

Habitat

Triangular spiders are found in a range of habitats throughout Australia, in particular the east coast of Australia. They are commonly found in eucalypt forests and woodlands, but can be found in gardens. They are often seen on trees, shrubs and on or under leaves.

Triangular spiders are also commonly found on plant regrowth after forest fires.

Distribution

Triangular spiders are found through out the Australasian region including Australia, Papua New Guinea, Indonesia and New Caledonia.

Seasonality

Most prevalent in summer.

Feeding and diet

Triangular spiders ambush their prey. They wait motionless, usually on the underside of leaves with their front two pairs of legs widely separated. When their prey passes by they capture it. Their sit and wait prey capture behaviour is similar to how flower spiders catch their prey.

Triangular spiders feed on insects, mainly flies.

Other behaviours and adaptations

Whilst triangular spiders are usually found on the underside of leaves by day, at night they are often seen moving along a silk line between leaves or hanging on a few lines with legs outspread.

Triangular spiders do not catch prey in webs, they use their silk for their egg sacs, for silk lines and holding on to leaves. They dab silk onto the leaf and are attached through the spinnerets as well as several legs.

Life history cycle

In late summer, females produce a small egg sac that can can contain around 50 eggs.

Danger to humans

Are harmless to human beings.

References

Main, B (1982) Notes on the reduced web, behaviour and prey of Arcys nitidiceps Simon (Araneidae) in South-Western Australia. Bull. Br. Arachnol. Soc: 5(9): 425-432