Observations on the behavioural sequences of looping and drifting by blackfly larvae (Diptera: Simuliidae)

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Abstract
Video equipment was used to record the behaviour of larval blackflies in a laboratory stream simulating natural current and substratum conditions. In this way it was possible to identify the following behavioural patterns associated with locomotion: 1. Landing: The first contact of drifting larvae with a new substratum was made with the mouthparts by means of a sticky secretion (silk). A “landing silk pad”; was created on the substratum, with the abdomen hanging freely in the current. The abdominal hook circlet was then fixed to the new silk pad. 2. Changing the attachment site: “Looping”; behaviour depended on whether the larvae were wandering across the substratum, or preparing for a long term attachment. 2.1. Wandering: Larvae moved across the substratum by displacing their mouthparts and thoracic prolegs alternately with the abdominal hook circlet. When building the “wandering silk pad”; the larval body was stretched ahead and anchored by the thoracic and posterior prolegs. 2.2. Transition to the “long term attachment site”;: Assuming a U‐shaped posture, the larvae formed the silk pad directly adjacent to the original site. They attached themselves for up to several hours, generally in order to filter feed.