THE MACHINERY OF INSECT FLIGHT* 



Edward G. Boettiger 

 University of Connecticut 



Nature, in the course of evolution, has experimented with the problems 

 of heavier-than-air flight. Three different solutions have proven success- 

 ful, and today birds and insects share with man the control of the air. Once 

 in possession of a supplementary power source, man required only knowl- 

 edge of the principles of flight to develop the airplane. The flying machinery 

 of birds and insects could furnish necessary clues, and so during the latter 

 half of the nineteenth century, many studies of animal flight were under- 

 taken. These provide the background of our present knowledge. 



Among birds, the mechanical aspects of the flight mechanism are quite 

 similar, while insects exhibit a variety that is obvious even to the casual 

 observer. The presence of an exoskeleton makes possible different me- 

 chanical arrangements to couple the driving muscles to the wings and gives 

 to insects the remarkable features of their flight : rapid starts and changes 

 in direction, hovering, and in some cases even backward flight. Insect 

 flight machinery includes many tiny structures moving in intricate designs, 

 and the muscles that move them. Our knowledge of this complex mech- 

 anism is still only fragmentary, but already new and exciting physiological 

 adaptations have been found. The intent of this paper is to consider in 

 some detail the most interesting of these — after a brief introduction to the 

 general features of insect flight. The appearance in recent years of an ex- 

 cellent review by Chadwick (1953) relieves me of the necessity of dealing 

 with the earlier work. As a source of information on power output of in- 

 sects in flight, one should study the beautiful experiments of Hocking 

 (1953) and of Weis-Fogh (unpublished) ; and for flight muscle histology, 

 morphology, and development, the recent work of Tiegs (1955). 



Classification and Distribution of Flight Mechanisms 



To sustain an insect in flight at its normal cruising speed requires the 

 consumption of relatively large quantities of fuel by the driving muscles. 

 Only 3-5% of the food energy can be used to give momentum to the air 

 flowing through the wings (Hocking, 1953). That the air flow can be 



* The original work discussed here was begun and carried out through several 

 summers in collaboration with Dr. Edwin Furshpan. Other students who have par- 

 ticipated in various phases of the work include Frances McCann, Richard Baranowski, 

 William McEnroe, and Rudolph Pipa. The generous financial assistance of the Na- 

 tional Institutes of Health made the study possible. 



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