Wildlife Talkback with Jess Price

Sussex Life - January 2014 cover

Sussex Life - January 2014 cover - Credit: Archant

With Jess Price of Sussex Wildlife Trust

Dip a net into almost any pond in the UK and you are likely to pull out a backswimmer. Also known as Greater Water Boatman, backswimmers are true bugs that can be found throughout the country. The official scientific name for this species is Notonecta glauca, but its common names come from its habit of swimming upside-down just under the surface of ponds.

Backswimmers are a light brown or green colour with reddish eyes, but often have a silvery sheen when they are in water. This is caused by bubbles of air that get trapped by the bristly hairs that cover the lower side of their body. The trapped air helps to prevent water getting into the spiracles - the openings that insects breathe through.

With a maximum size of about 2 cm, the backswimmer is relatively small, but it is still a ferocious hunter attacking prey as big as tadpoles and small fish. They can even catch the fearsome larvae of the great diving beetle.

Backswimmers hunt by sensing vibrations in water. They float motionlessly at the surface until they detect a movement nearby. Their eyesight only becomes useful at near distances i.e. an inch or two, so it uses its oar-like rear legs to propel itself through the water to get close enough to its potential prey. They kill by injecting toxic saliva, using the hard feeding tube, called the rostrum, which is a feature of all true bugs. Be careful when pond dipping as backswimmers can give a nasty nip which is not poisonous to us, but can certainly be painful.

Backswimmers can be found in most freshwater habitats with still or slow moving water. The adults are able to fly and will colonise areas quickly. They are often one of the first creatures to arrive in a new garden pond. Mating occurs in winter and spring with eggs being laid in submerged plant stems between February and May. The larvae are white or greenish and look fairly similar to adults. It takes two months for backswimmer larvae to become adults as they undergo a series of moults.

Backswimmers should not be confused with Lesser Water Boatman (Corixa punctata). Although the two species look similar and are both common, they are not closely related. Lesser water boatmen swim on their fronts and are vegetarian, feeding mostly on algae.