Collective Behavior of the Whirligig Beetle

Abstract

Whirligig beetles live on the surface of the water and aggregate for three evolutionary reasons: predation risk, thermoregulation and anti-predator chemical concentration. If a predator were to strike from above or below, the distance of an individual’s neighbors determines the area over which that individual may be the nearest prey available to the predator, which determines its chances of being predated. By grouping, organisms are also often able to raise their body temperature through reduction in convective heat loss. They are also able to raise their collective concentration of a chemical called gyrinidal. While all three of these reasons are affected by the number of individuals in the group, they’re also affected by the density of the group itself. In this thesis, we ask how we do whirligig groups actually pack in comparison to the optimal packing for their body shape, and how does packing scale with group size? By establishing a link between density and group size, we’ve identified another way in which the benefits of grouping scale with group size. This analysis is performed through image analysis of the beetles and through monte-carlo simulations.