Another week has passed and with it the BIObus crew says goodbye to another of Canada’s national parks. Prince Edward Island National Park, while relatively small compared to the other parks, was not lacking in unique ecosystems to explore and research. From dunes of the extensive beaches, to sandy swamps, to mixed forests, there was no lack of things to do in P.E.I..
During one of our hand collecting events along the short Reeds and Rushes trail we came across a fairly incredible sight, though one that may easily be overlooked by the casual passerby. Thousands of small, black beetles were skittering across the pond’s surface, swimming in circles and reacting to us in waves of activity as we approached the water. Upon closer examination of the behaviour of the beetles, it appeared that they were haphazardly colliding with each other, though there was undoubtedly some sort of order or coordination to their movements. Dashing across the pond were thousands of (the aptly named) Whirligig beetles.
The Whirligig beetles, of the family Gyrinidae, are easy to spot in their adult forms due to their conspicuous appearance along the water’s surface and bizarre locomotory patterns. Many of these beetles can both swim below the surface and fly, though primarily they can be found as surface swimmers. If you’re lucky enough to examine one of the adults under a microscope, you will quickly notice a bizarre and amazing morphological feature: each of the eyes is divided into two separate halves, one for vision above the water and one for vision below the water’s surface. This is an adaptation I would consider an evolutionary triumph, the split-eye morphology secures the whirligig beetle’s dominance over the thin line that separates air and water. With the ability to spot predator, prey or potential mate in either zone and to react appropriately allows this organism to thrive.
It is no mistake that when we saw the Whirligig beetles we saw them in droves. Research suggests there is a level of complexity to their group structure that is based off of a number of variables that determine their position within a group. For instance, individuals that are hungrier tend to be on the periphery of the group, presumably to allow for greater opportunity to feed on detritus and other prey items.
Another fairly amazing feature of the Whirligig beetle is the physical gill it possesses. This physical gill occurs in the form of an air bubble held beneath the wing covering (the elytra), a fairly conspicuous feature when viewing an individual swimming below the surface of the water as a clear bubble of air is held against the rear-end of the insect. This bubble of air operates through the passive diffusion of oxygen from the water to the Whirligig beetle, allowing for a potentially indefinite stay under the surface. Incredible!