|Outside view, with flash and quadruple reflections.|
|From the inside, no flash.|
Since this spring, I have been working my way through a college textbook on invertebrates. (Living Invertebrates, Pearse/Buchsbaum) It's a fascinating read. A few weeks ago, I came across this fact: see those two little knobs sticking out from the sides of the crane fly? They are all that remain of the second pair of wings many other insects (bees, beetles, dragonflies, butterfies, etc.) have. The flies belong to the order Diptera, meaning "two-wings"; they only have one pair of wings and these useless-looking knobs.
That I knew; what astounded me was that, if you cut off these tiny halteres, the insect can't fly.
The halteres serve as balancing rods and part of the fly's guidance system. Both of them flap up and down when the wings do, but out of phase with the wings, each one vibrating, as well, in a different plane. As the fly's body turns in flight, sensory organs at the base of each haltere register the resistance of the knob to this change; this information enables the flies to control their flight, and incidentally, to thumb their noses at me and my fly swatter.*
This kind of work revealed why, while fleeing a rolled-up newspaper, for example, a fly can carry out a right angle turn in as little as 30 thousandths of a second. The secret seems to rest in their halteres, a pair of club-shaped organs that beat out of phase with the wings. Prof Dickinson found they act as critical way-stations for information from the insect's brain, taking visual cues from the eye and then relaying them to wing-steering muscles, in addition to making counter motions to help to end a turn. (From The Telegraph, 2005)
*Used mainly for mosquitoes. Which escape to bite another day, as often as not.