Flies Flying-By

Flying about in a crowded airspace is difficult enough, but the biggest problem is landing. Not just anywhere mark you, but on a precise spot that is coming up fast and is often moving. Of course, birds do it and bees do it, but so do fruit flies.

Fruit flies aren’t very large and have to rely on their in-built guidance systems to reliably work on the fly.  Van Breugel and Dickinson, in the current edition of the Journal Of Experimental Biology have been scrutinizing the success and failure of fruit fly landing sequences with a combination of high-speed photographs and 3-D tracking software (1).

The touchdown sequence commences with a sharp turn towards the target and a deceleration that the authors explain is governed by the growth of the image size on the fly’s retina. The go/no-go decision is made at the point that the target image takes up an include angle of about 33 degrees of the fly’s vision field.

If the decision is go – the deceleration sequence continues until the target image angle has increased to about 60 degrees and then the landing gear is deployed. On touch down the feet grasp the target. From gear deployment to touchdown was about 50 ms – pretty fast reactions are a must.

If the no-go decision is called for, the fly’s fly-by procedure is a sharp turn away and off to another target. This occurred in 1065 attempts out of 1242-recorded measurements.

Flies flying-by may have been due to too fast an approach or maybe just the fickleness of the fly. They did record some crash landings when flies came in too fast and failed to abort, but none included any fatalities.

  1. http://jeb.biologists.org/content/215/11/1783

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