THE HABITS AND NATURAL HISTORY OF THE 

 BACKSWIMMERS NOTONECTIDAE 



CHRISTINE ESSENBERG 



From the Zoological Laboratory oj the University of California 



The purpose of this article is to record observations made 

 on the aquatic Hemiptera Notonectidae. These insects were 

 chosen for the experimental work because they are found in 

 great abundance and because very little is known about their 

 behavior. The work was done in the Zoological Laboratory of 

 the University of California under Professor S. J. Holmes, to 

 whom I wish to express my gratitude for kind suggestions, and 

 criticisms. Thanks are also due to Professor C. E. Van Dyke 

 for his help in determining the species. 



The Notonectidae are commonly known as backswimmers 

 from their habit of swimming on their backs. They are widely 

 distributed, extending from the arctic to the tropical regions. 

 Kirkaldy has recorded about twenty different species of Noto- 

 nectas. According to J. R. de la Torre, Bueno, twelve of these 

 species are peculiar to America. The bugs here described were 

 collected in a small pond on the university grounds, the species 

 identified being four in number, Notonecta insulata Kirby, 

 Notonecta undulata, variety Charon, Notonecta indica, and an 

 unidentified spec es. The last named is most abundantly rep- 

 resented. Notonecta insulata is the largest of the four species, 

 ranging in size from five to five-tenths mm. in width. It is 

 usually of a dark or bluish-black color. Notonecta undulata 

 and Notonecta indica are smaller and more slender than Noto- 

 necta insulata. Notonectas show many striking adaptations to 

 aquatic life : their backs are convex and boat-shaped, the ventral 

 surface being flat. The hind legs are long, specially flattened 

 and fringed, thus serving as oars. The two pairs of forelegs 

 are sparsely covered with hairs and are provided with claws. 

 The latter serve for the capture of food and for attachment to 

 the surface film, from which they hang with their heads down- 

 ward, the posterior part of the ventral surface being exposed 



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