Greater water boatman are often one of the first species to be spotted in a pond. Look into a pond in on a warm day and you might see a set of 3 ‘dimples’ in the waters surface. Look closely beneath these dimples and you will see they are made by 2 legs and end of the abdomen of a water boatman in its typical upside down resting pose. This habit of hanging from the surface and swimming upside down has given them the alternative name of backswimmer.
Once caught they can be recognised from their boat shape body with a keel, their red eyes and their pair of long oar like legs, which gives rise to the boatman in their name.
The backswimmer is somewhat infamous among pond dippers for being a biter. Of course being true bugs they don’t have any mandibles to bite with and rather stab with their needle like rostrum. This rostrum has formed as the 3 pairs of mandibles have evolved, with one pair forming the outside of the tube and 2 pairs inside which can be extended to pierce their prey. As predators this rostrum is used to inject digestive enzymes before sucking out the digested and liquidised insides. In one area of Spain this insect is referred to as “garapito”, which happens to be the name of a former tax collector, perhaps a reference to the insect sucking its prey dry!
Prey includes other invertebrates, both aquatic and terrestrial that fall into the water. They will also take prey larger than themselves, including vertebrates like amphibian tadpoles and fish.
They detect prey by 2 different methods. Their first is their large red compound eyes, which have some overlap giving stereoscopic vision and depth perception in these directions. They also locate prey by detecting the vibrations made by their prey swimming or the struggles of an insect stuck in the surface tension.
There are 4 species of Notonecta found in the UK:
N. glauca, the common backswimmer
N. maculata, the mottled or spotted backswimmer
N. viridis, the small or x backswimmer
N. obliqua, the bog or moorland backswimmer
Th adults breathe air by periodically returning to the surface to replenish their supply, using hydrophobic hairs at the tip of the abdomen to allow it access to air through the waters surface. The air diffuses through the bubble of air form on the underside of the abdomen by a large number of small hydrophobic hairs, which also act as a physical gill, allowing oxygen to diffuse in from the water and carbon dioxide to diffuse out.
They overwinter as adults in ponds and breed in spring, with the adults often flying from overwintering ponds to ponds that have refilled with winter rain. Once mated the eggs are laid on or in aquatic plants and they hatch into miniature versions of the adults, feeding on smaller prey such as water fleas, and sometimes other nymphs!