236 



BULLETIN OF THE BUREAU OF FISHERIES. 



slow. Yet the Pel tody tes larva, when ready to pupate, travels farther from the 

 water's edge than the much larger Cybister or Hydrous larva. 



Leng (1913, p. 35) made a curious statement with reference to these larvae: 

 ''The larvae of the Haliplidae, Dytiscidae, Hydrophilidae, Gyrinidse, and Parnidae are 

 purely aquatic, living wholly in the water, but not swimming." This applies only 

 to the Parnidae and Haliplidae; the others can and do swim. 



The adult beetles can walk, run, jump, swim, and fly with varying ability. Fly- 

 ing is the means of locomotion by which they travel from one body of water to 

 another and so disseminate their species. The larger species of dytiscids and hydro- 

 philids can cover long distances and are sometimes found at night around electric 

 lights far removed from any water. Many instances of their capture about these 

 lights are recorded by Sherman (1913) in his paper on ''Some Habits of the 

 Dytiscidae." Needham in "Fresh-water Biology" (1918, p. 905) said of Hydrous: 

 "It is attracted to electric lights in vast numbers in the spring, where it falls 

 beneath them and flounders around in the dust of the street, * * Another 

 hydrophilid, which often swarms into trap lanterns set over streams, is Berosus." 

 Yet most of the adults can be safely kept in an open aquarium. Though the g3rrinids 

 have to climb up on some support above the water before they can spread their 

 wings for flight, yet once started, they prove to be strong fliers, for Fall (1901, 

 p. 55) has recorded: "I have seen hundreds of Gyrinus consohrinus about the 

 electric lights at Riverside (Calif.) in May." 



The order of excellence in swimming and walking amongst a series of representa- 

 tive adult dytiscids has been determined by student classes at Lake Forest for a 

 number of years, and, with the addition of jumping, was published in the Ameri- 

 can Naturalist (Needham and Williamson, 1907, p. 480). The general conclusion 

 that increasing fitness for swimming accompanies increasing unfitness for walking 

 and running seems to be well established. Incidentally it may be noted that the 

 Gyrinidae show this nearly as well as the Dytiscidae. Swimming with such swift- 

 ness and agility that it is almost impossible to catch them without a net, once they 

 are removed from the water they prove to be very poor walkers, and can not run 

 at all. 



Jumping seems to be a function peculiar to the dytiscids and gyrinids, and so 

 far as known is not found at all among the hydrophilids and haliplids. There 

 is another dytiscid whose jumping ability exceeds that of LaccopJiilus maculosuSj 

 the champion of the Lake Forest tournaments. This is Thermonectes ornaticoUis, 

 which, when captured in a net, leaps about like a small frog. Another peculiarity, 

 not mentioned by Needham and Williamson, is that both Laccophilus and Ther- 

 monectes can jump when lying on their backs as well as when right side up. The 

 ability to jump is evidently dependent upon the flattening of the hind legs, which 

 brings the basal joints into one plane of action, and greatly increases their effi- 

 ciency in that plane. To compensate for the lack of ability to jump, all the adult 

 hydrophilids and haliplids are good walkers, and many of the former can run with 

 agility. 



The relative swimming ability of the dytiscid and the hydrophilid is well shown 

 when they come to the surface for fresh air. The hydrophilid swims well but not 



