Seasonality of prey size selection in adult Sympetrum vicinum (Odonata: Libellulidae)


Sympetrum vicinum is a sit and wait predator, which takes off and pursues small flying insects during its long flying season (July to November). We investigated whether foraging individuals become less discriminating regarding prey size selection during the fall season because the changeable fall weather has an impact on the prey population. To investigate the seasonality of prey size selection, we videotaped prey capture flights of females and tenerals chasing artificial prey of known sizes (1–8 mm beads) from September to October in 2002 and 2003 in upstate New York, USA. We calculated the probability of pursuit for each bead size and measured the distance of the bead at the time of takeoff (213 presentations in 2002 and 383 presentations in 2003). We found that 2 mm beads had the highest probability of eliciting takeoff in both years and throughout the study periods. Weather conditions, especially the early first hard frost in 2003, reduced prey abundance. S. vicinum opportunistically pursued a wide variety of prey sizes. The probability of pursuit of larger beads (3–5 mm) increased in late fall, but S. vicinum never pursued 8 mm beads. The mechanism of distance perception and therefore size detection is not known in Odonata and yet S. vicinum in this study is showing a preference for 2 mm beads no matter what the distance of the bead from the perch.

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