February 2016

Stick-like aquatic predator

We found this little guy in our swimming pool and were wondering if you could identify it? Our creeks have no water at the moment so where does it usually live? Is it even a water animal?

Answer

It may look awkward and gangly but this needle bug with its stick-like body is able to capture fast-moving prey. Image courtesy: Chantal Radoll Water Scorpion

The creature in your swimming pool is a needle bug. This insect belongs to the subfamily called Ranatrinae which is part of a larger group known as water scorpions (family Nepidae). Although they look like stick insects, they are actually more closely related to cicadas and stink bugs.

Needle bugs and other species of water scorpions live in wetlands, ponds and at the edges of slow-moving waterways. When under water they breathe through a long tube-like structure. They are the only aquatic bugs to have such a breathing tube; this makes identifying them relatively easy.

To locate their prey, these ‘sit-and-wait’ predators use their good eyesight and possibly also organs on their forelegs that are sensitive to vibrations.

When they hunt, needle bugs hang upside down with their breathing tube sticking out of the water and wait for prey to swim past.

They use their forelegs to capture quite fast-moving animals such as fly larvae, water boatmen, small shrimp and tadpoles. They feed by piercing the victim with a segmented proboscis or ‘beak’ and sucking out the body fluids.

Like many aquatic insects, these bugs can fly. This ability allows them to colonise new water bodies and explains why they are sometimes found in recently formed ponds and puddles after rains or flooding.

So the needle bug is an aquatic insect that breathes through a ‘snorkel’ on its abdomen, catches prey with its front legs, and can fly!

For more information please download our Water Bugs and Water Scorpions fact sheet (293 KB) pdf document icon.

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