Journal of Comparative Physiology A

, Volume 169, Issue 4, pp 451–459

A visually evoked escape response of the housefly

  • Mats H. Holmqvist
  • Mandyam V. Srinivasan

DOI: 10.1007/BF00197657

Cite this article as:
Holmqvist, M.H. & Srinivasan, M.V. J Comp Physiol A (1991) 169: 451. doi:10.1007/BF00197657


Flies (Musca domestica) avoid danger by initiating a rapid jump followed by flight. To identify the visual cues that trigger the escape response in the housefly, we measured the timing and probability of escapes when the fly was presented with a variety of visual stimuli created by moving targets toward it. Our results show that an escape response is triggered by an approaching dark disk, but not by a receding dark disk. On the other hand, a bright disk elicits escape only when it recedes. A disk with black and white rings is less effective at eliciting escape than is a dark solid disk of the same size. This indicates that the darkening contrast produced by an approaching stimulus is a more crucial parameter than expansion cues contained in the optical flow. Escape is also triggered by a horizontally moving dark edge, but not by a moving bright edge or by a grating. An examination of several visual parameters reveals that the darkening contrast, measured from the onset of stimulation to the start of escape is nearly constant for a variety of stimuli that trigger escape reliably. Thus darkening contrast, coupled with motion may be crucial in eliciting the visually evoked escape response. Other visual parameters such as time-to-contact or target angular velocity seem to be relatively unimportant to the timing of escapes.

Key words

FlyVisionEscape responseMotionGiant fiber pathway



Probability of successful escape


radius of disk target


radius of shielding arena


linear velocity of disk target


linear velocity of edge


angular velocity of disk target boundary


angular velocity of edge


target distance at escape


target distance before onset of target movement


height of the edge above fly


distance from corner of triangle to start position of edge (0 or 50 mm)


distance from corner of triangle to the position of the edge when the fly escapes


distance from corner of triangle to point above the center of the pad


distance from the corner of the triangle to the base (height of triangle = base of triangle)

Copyright information

© Springer-Verlag 1991

Authors and Affiliations

  • Mats H. Holmqvist
    • 1
  • Mandyam V. Srinivasan
    • 1
  1. 1.Centre for Visual Sciences, Research School of Biological SciencesAustralian National UniversityCanberraAustralia