Back swimmer (Anisops)

Taxonomic group

Notonectidae: Anisops

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.

[Anisops]. Long, oar-like hind legs. Image: Stephen Moore Image — Anisops. Long, oar-like hind legs. Image: Stephen Moore

[Anisops]. “Belly” facing upwards when swimming. Image: Stephen Moore Image — Anisops. “Belly” facing upwards when swimming. Image: Stephen Moore

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

Hard bottom: 5
Soft bottom: 2.2

The tolerance values (ranging from 0 to 10) give an indication of which are the sensitive taxa (values of 8 or more) and which are the tolerant taxa (values of 3 or less). For more information see: Indicator species

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).