Dispersal and Migration

Aciagrion occidentale

Dispersal is perhaps the most relevant and least understood mechanism in odonates.  Since odonates are good fliers, it is difficult to track them by direct observation and quantitative records are rare.  It is generally observed that big and powerful fliers have wider geographic range than small and weak fliers do.  Many damselflies make use of their light weight and depend on air currents for dispersal. It has been observed that they will rise almost vertically into the air to the air currents, which will then carry them away.  Fraser (1933) has reported encountering Aciagrion occidentale (a damselfly) from 40 miles out at sea off the western shores of India and Sri Lanka.

According to Corbet (1999), migration in odonates can be defined as spatial displacement that entails part of (or an entire) population leaving the habitat where emergence took place and moving to a new habitat in which reproduction takes place.  Depending on the species, migration can be facultative or an obligate part of life cycle.  Obligate migration is typically associated with temporal habitat discontinuity imposed by seasonal drought or cold.  In the tropical regions, seasonal movements of the Intertropical Convergence Zone (ITCZ) cause the seasonality of the rainfalls associated with it.  The well-known migratory species, Pantala flavescens travels with the air masses bringing the rains which enable this species to exploit temporary pools as larval habitat.

Recent studies of the migration of Pantala flavescens (Anderson et al. 2009) indicate that this species uses monsoon winds to cross the Indian Ocean.  Anderson proposes that P. flavescens, in four generations, would cover a total distance of at least 14000 km aided by alternating monsoons.  According to him, they would breed in equatorial East Africa in October-November, in Southern Africa in December-February and again in East Africa in March-May, before returning to India with the ITCZ in June-July. 

Several Aeshnidae members are also known to be migratory.