ABSTRACT

The term ‘swarm’ has been applied to a variety of aerial mating systems. All are supposedly non–resource–based, although their relationship to resources is sometimes ambiguous. There are several selective contexts for mate choice. The choice of swarm markers has been implicated in species isolation. However, certain swarm markers are used by multiple species, which suggests that qualities other than specificity are important. In some instances, species appear sequentially at a marker, and there is evidence that not all times of day are equally valuable for swarming. It is not clear whether species compete for a universally best time. Swarms themselves, as well as markers, can attract participants, and a swarm's size can contribute to its attractiveness. The position of an insect within a swarm might influence its sexual opportunities. In species where male size is positively correlated with reproductive success, there is an instance where larger individuals occupy certain parts of the swarm. There are more observations of homogeneous size distributions in swarms, although in some species from several families of Diptera, the smallest males swarm very little or not at all. Presumably, they lack the energy resources to compete with larger males. Swarming insects may emit sexual signals. Pheromones seem to be rarely used, perhaps because of difficulties in determining the source of the signal. Visual signals are the easiest to trace to their sender, and furthest projected. Vision seems to be the paramount sense in swarming species.