Larvae of the net-winged midges possess 6 ventral suckers that are used for maintaining position in torrential habitats and for walking. Although the structure and function of these suckers are well known, reports about the locomotory behavior of blepharicerid larvae remain contradictory. Using video macroscopy and digital image processing, the locomotory behavior of Liponeura cinerascens minor, L. cinerascens cinerascens, and Hapalothrix lugubris was investigated. Observations were conducted in a high-speed flume at 1.4 m/s and 2.0 m/s (except for L. cinerascens cinerascens). Six basic locomotion patterns were quantitatively described and analyzed: 1) straight forward movement, 2) backwards movement, 3) slow sideways movement, 4) rapid sideways movement, 5) re-orientation and 6) foraging. In addition, a defensive behavior sometimes preceded the rapid sideways movement. Movement speed ranged from 0.1 mm/s (foraging behavior) to 0.96 mm/s (rapid sideways movement). Movement patterns of all locomotion types, except foraging, seem to be stereotypic (i.e., constant) in reference to all suckers, whereas foraging behavior is primarily governed by the cephalic division. The results indicate that some types of locomotion differ between H, lugubris and Liponeura spp. During all types of locomotion, the larvae remained attached most of the time by at least 2 suckers. This minimal number apparently allows maximal mobility and speed, yet guarantees mechanical stability and safe attachment.
