Department of Zoology, University of Cambridge

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Hovering and forward flight in Eristalis

Syrphids (hoverflies) are extremely agile and adept fliers, capable of motionless hovering, accelerations of at least 3g from stationary hovering, and flight speeds approaching 10m/s over short bursts. The drone flies Eristalis tenax & E. pertinax are ideal study animals due to their abundance in the natural environment and propensity to fly even under hot, strongly lit laboratory filming conditions. Wild collection has provided sufficient filming specimens, although in addition eggs laid by captured females have been successfully reared through the larval & pupal stages to give more adult flies for filming.

High speed footage is obtained with a Phantom 7 high speed digital video camera fitted with Nikon optics. Kindly loaned to me by the EPSRC Instrument Loan Pool, this outputs crisp images at 4800 frames per second, effectively separating each wing stroke (there are 175 per second) into 27 images for analysis. The image above is a still image extracted from a video sequence taken using this camera. In the video (click on the text below), Eristalis pertinax hovers between two calibration pins.

The 3-dimensional kinematics will be recorded from these images, as well as the base morphological data that has been recorded from the flies themselves. The wings of all the filmed flies are preserved to aid the construction of model wings. Simple rotor-based dye flow modelling will be conducted to indicate qualitatively the type, character & magnitude of the translational components of the wing stroke cycle.

Smoke rakes will be used with subsequent filming of the flies. Although larger than most Syrphids, Eristalis is smaller than most insects where smoke rakes have been used. If successful, this will provide detail of the air flow and resultant forces pertaining to the rotational component of the wing cycle

Forward flight will require additional analytical complexity, although the filming system has already yielded exceptional images of forward flight in Eristalis. It would also be constructive to compare the Eristalis kinematics with those of Volucella pellucens & Helophilus pendulus (two species different in size to Eristalis that have already proven to be readily caught & filmed) in order to examine scaling effects.

Last updated July 2004
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