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Back swimmer

Guide to New Zealand's freshwater invertebrates

Back swimmer ( Notonectidae : Anisops )

Long, oar-like hind legs
“Belly” facing upwards when swimming

Diagnostic features

Anisops bugs have elongated hind legs designed to act like oars. Anisops is often referred to as the “backswimmer” because it swims with its “belly” facing upwards, unlike the other common swimming bug Sigara (water boatman). Also unlike Sigara, the forelegs of Anisops do not end with a trowel-like segment.

Typical habitats

Anisops are most common in ponds and lakes, but they can also be common in the backwaters of streams and rivers.

Feeding

They are predators, feeding on other pond invertebrates.

Indicator value

An abundance of Anisops is likely to be the result of pond-like habitat conditions (at the site or upstream) rather than any particular water quality condition. They have medium to low tolerance values of 5 (hard bottom sites) and 2.2 (soft bottom sites).