"He has an inordinate fondness for beetles," so the famous biologist, J.B.S. Haldane, described God a reference to the fact that there are more than 250,000 known species of beetles. Haldane would have come to a different conclusion if he had just sampled the Arctic! There are only 167 different beetles reported from the Arctic, and most of these are restricted to the low Arctic. The vast majority of beetles are terrestrial, but on a number of occasions, beetles have invaded freshwaters. Each beetle group that invaded water adapted differently to aquatic conditions because aquatic beetles are diverse in form and behaviour.
All beetles have caterpillar-like juvenile stages. Unlike caterpillars, however,
beetle larvae have well developed legs. The larvae of aquatic species have some
distinguishing features that set them apart, such as the presence of gills on
their thorax. Some aquatic beetles do not have gills, but instead capture an
air bubble at the water surface and carry it with them underwater as a source
of oxygen while they swim. In adult beetles, this bubble appears as a silver
sheen on their bellies. The arctic beetle, Hydroporus melanocephalus,
is one example of this adaptation.
Some aquatic beetles are voracious feeders. Several species from the family
Dytiscidae, the predacious diving beetles, occur in the Canadian Arctic, and
two species reach the High Arctic. Their larvae are known as water tigers, because
of their huge, rounded jaws that are excellent weapons in the capture of prey.
The water beetles then inject their captured prey with enzymes to turn their
insides into "soup" and use their hollow jaws like straws to suck
out their prey's insides. Like most other aquatic species of beetle, the adults
in this group have a rounded, compact body and a thick, solid "shell"
(exoskeleton). Using their legs as oars, they race through the water
at high speeds, capturing insects, crustaceans, and even small fish. These beetles
breathe by capturing air beneath their wing coverings, the elytra, but
they also readily use their wings for their primary purpose flying from
pond to pond.
A few species of beetles from other aquatic families are known to occur in ponds throughout the Low Arctic. The small, crawling water beetles, Haliplidae, have one Arctic representative, which feeds on algae. A few species of water scavenger beetles also occur in tundra ponds. These dark-coloured, oval beetles have a long, sharp beak that is used to suck the nutritious juice out of the corpses of other aquatic invertebrates.