Net-casting spider fact sheet | Field of Mars EEC

What are net-casting spiders?

Net-casting spiders are unusual spiders that hunt with a small stretchy silk net. They hang head-down at night, hold the net in their front legs and throw it over insects and other small prey. In Sydney bushland and gardens, the species students are most likely to see is the rufous net-casting spider, Asianopis subrufa. Older books and image files may still use its old scientific name, Deinopis subrufa.

Net-casting spiders have long thin legs, a narrow body and eight eyes. In the rufous net-casting spider, two of these eyes are much larger than the others and face forwards like small searchlights. These large eyes help the spider detect prey movement at night.

A net-casting spider.

A rufous net-casting spider holds a small silk net ready to throw over passing prey.

Where do net-casting spiders live?

Net-casting spiders live among shrubs, trees, low vegetation, bark and leaves. They are found in forest, woodland, heathland, bushland and gardens. During the day they often hide among leaves or twigs, where their long narrow body helps them blend in.

At night they become active. They often hunt above a leaf, tree trunk, bark surface or wall where insects may walk past. Their small net is usually made among low vegetation and can be left suspended for reuse if it is not damaged.

Young net-casting spiders can be difficult to see when they rest like a twig.

How do net-casting spiders catch their prey?

Net-casting spiders have one of the most unusual hunting methods of any spider. At night they make a small rectangular net from thick, stretchy, bluish-white silk. The spider hangs head-down from silk support lines and holds the net in its front legs.

The spider often places white spots below the net as aiming marks. When an insect walks across the target area, the spider opens the net to two or three times its resting size and lunges downward. The silk stretches over the prey and tangles it. The spider then bites, wraps and eats its catch.

The small net is made from stretchy silk that can expand over prey.

What do net-casting spiders eat?

Net-casting spiders are predators. They eat insects and other small invertebrates, including ants, beetles, crickets, cockroaches, moths and other spiders. They can catch prey walking below them and may also strike at flying insects that come too close.

By catching insects and other arthropods, net-casting spiders help keep food webs balanced in bushland and gardens. They are also food for other animals such as birds, reptiles and larger predatory invertebrates.

Net-casting spiders wait quietly at night before lunging down with their silk net.

What is the life cycle of a net-casting spider?

Net-casting spiders mature in summer, with mating and egg-laying occurring into autumn. The female makes round egg sacs that are about 9–10 mm across. These egg sacs are covered in tough brown or salmon-brown silk and may be disguised with bits of leaf litter. They are usually suspended from low vegetation by a short silk stalk.

Spiderlings hatch from the egg sac and begin life as tiny versions of the adult spider. After a short time, they begin to make their own tiny nets. As they grow, they shed their outer skin several times before becoming adults.

A female net-casting spider makes a protective silk egg cocoon.

Net-casting spider egg sacs are round and may be hidden among leaves and twigs.

What adaptations do net-casting spiders have to help them survive?

Net-casting spiders have many adaptations that help them survive. Their large forward-facing eyes help them see movement at night. Their special wool-like silk stretches over prey and tangles it. Their long thin body helps them look like a twig when they are resting. Hanging head-down also helps them stay ready to strike quickly.

Their behaviour is also an adaptation. Instead of chasing prey, they wait in the right position, use aiming spots and throw their net at the right moment. This helps them catch insects while using little energy.

Net-casting spiders have large eyes to help see movement at night.

Why are net-casting spiders important?

Net-casting spiders are important because they are predators in bushland and garden food webs. They help control populations of insects and other small invertebrates. They are also part of the diet of larger animals. Like other spiders, they show how important invertebrates are in healthy ecosystems.

Net-casting spiders are also fascinating because of their unusual hunting behaviour. Their large eyes, stretchy silk and net-throwing technique help scientists and students learn more about animal adaptations.

Net-casting spiders help to control the population of insects in natural areas.

How can you help net-casting spiders?

You can help net-casting spiders by protecting bushland and leaving natural habitat in gardens. Leaf litter, bark, shrubs and low vegetation provide places for spiders and their prey to live. Avoiding unnecessary pesticide use also helps protect spiders and other invertebrates.

If you find a net-casting spider, leave it where it is. Watch carefully, take a photo if you can do so safely, and avoid breaking its silk support lines.

Leaf litter, bark and low plants provide shelter for spiders and other invertebrates.

Related fact sheets

More invertebrate fact sheets

• Spider fact sheet – Learn about spider body parts, silk, prey and how spiders live.
• Arachnids fact sheet – Compare spiders with other arachnids, including mites, ticks and scorpions.
• Flower spider fact sheet – Another plant-dwelling spider that hunts without using a large capture web.
• Jumping spider fact sheet – Another spider with excellent eyesight and active hunting behaviour.
• Wolf spider fact sheet – A ground-hunting spider that also relies on movement, camouflage and sensory adaptations.

Habitats and ecosystems

• Shrub habitats fact sheet – Explains how shrubs provide shelter, hunting places and habitat for small animals.
• Leaf litter habitats fact sheet – Explores the ground-layer habitat used by many small invertebrates.
• Eucalypt forest fact sheet – Explains the local bushland habitat where spiders and other invertebrates live.
• Field of Mars Reserve fact sheet – Explores the reserve habitats that support spiders, insects and other small animals.

Food webs and ecological relationships

• Praying mantid fact sheet – Another invertebrate predator found in bushland, shrubs and gardens.
• Fly fact sheet – Explores a common group of insects that can be prey for spiders.

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