WATER BEETLES IN" RELATION TO PONDFISH CULTURE. 



237 



rapidly, turns on its side as it reaches the surface, pauses an instant, and then 

 swims back to the plants below. The dytiscid sweeps to the surface like a flash 

 and without a sensible pause darts back again. The direction of its movement 

 is the only indication that it has obtained a new supply of air. The actual taking 

 of the air is too rapid to be detected, although it can be plainly seen in the 

 hydrophilid. Miall (1895, p. 74) has noted another difference between the swimming 

 of the hydrophilids and dytiscids. The former, together with the haliplids, use their 

 oar legs alternately, whereas the latter move them in unison. In other words, the 

 dytiscids gallop, but the hydrophilids and haliplids merely trot, and there is a 

 corresponding difference in the rapidity of the resultant motion. The inability to 

 jump on the part of these last two beetle families may be due to the fact that they 

 can not, or at least do not, move their hind legs in unison. 



To summarise, the adult dytiscids are excellent swimmers, excellent jumpers, 

 and poor walkers, without any ability to run. The hydrophilids are good swimm'ers, 

 good walkers, and good runners, but can not jump at all. The gyrinids are excellent 

 swimmers, fair walkers, poor jumpers, and can not justly be classed as runners. 

 The haliplids are excellent walkers and can run with considerable agility, but are 

 very slow swimmers and can not jump. 



MIGRATION FROM ONE POND TO ANOTHER. 



The marked differences in the fauna of adjacent ponds and the restriction of so 

 many species to comparatively limited areas is the more remarkable in view of the 

 rapidity with which a new pond is populated when filled with water for the first 

 time. 



The following is taken from manuscript notes made by Geo. B. Lay during the 

 summers of 1916 and 1917: On the morning of July 22, 1916, water was first 

 let into two newly constructed ponds, numbered 2 and 3, series E. At 4.30 p. m. 

 the ponds were full of water, but absolutely devoid of beetles. 



After standing for 24 hours the following beetles were obtained from the two 

 ponds, Dineutes americanus, Gyrinus ventralis, G. limbatus, Hydrous triangularis, 

 Tropisternus lateralis, Coptotomus interrogatus , Berosus striatus, Peltodytes edentu- 

 lus. On the 25th Laccofhilis maculosus was fairly abundant, and a few Lacco- 

 fhilus proximus, Acilius semisulcatus, and Haliplus triopsis were taken. One 

 Eydroporus consimilis was captured. On the 26th seven adult Hydrous triangu- 

 laris were secured from pond 3, and 18 from pond 2. Two egg cases were found 

 in pond 3 and one in pond 2, and in both ponds the eggs hatched a few days later. 

 On the 27th six more adult Hydrous triangularis were captured in pond 2 and five 

 in pond 3. On the 28th Dytiscus hyhridus was taken in pond 3, and there were a 

 few small larvae in both ponds. These observations show how quickly any pond 

 situated near others will become populated with adult insect life. 



In 1918 pond 2E was drained July 9 and left absolutely dry until August 15, 

 when it was refilled. During this month the bottom of the pond became hard 

 and thoroughly baked in the hot sun, so that all insect life was destroyed. The 

 present author examined the pond August 16, the morning after it was filled, and 

 found the following beetles in it: Tropisternus lateralis, abundant; Coptotomus 



