Hovering and Swarming Behavior of Male Tabanus calens (Diptera: Tabanidae) in Tennessee and New Jersey, USA

Hovering and swarming activity of male Tabanus calens L. were documented at distinctive sites above a woodland road clearing in Knox Co., TN (7 d), and above a slow-flowing river in Morris Co., NJ (6 d). Activity was restricted to the period near sunset. Mean activity typically began about 10 min before sunset and continued until about 10 min after sunset, with an average duration of 18.7 min (Tennessee) and 20.8 min (New Jersey). Swarming began earlier and thus lasted longer (55 min) on one cool New Jersey date. Onset and particularly cessation of activity tended to be statistically correlated with sunset time. Most males hovered at heights of 5-8 m in Tennessee, and they hovered in stable locations for a median of only 10 s (maximum 2 min 57 s) before darting away. Hovering in New Jersey was observed from 0.5-8.0 m above the water. The behavior of T. calens might be especially interesting to study in more detail, given its unusual eye morphology (lack of obvious dorsoventral facet size differences found in males of most other Tabanidae).