Fig. 13:21. Gyrinfdae, larvae, a, Dineutus sp.; b, Gyrinus sp. 

 (a, Wilson, 1923; b, Miall, 1903). 



the upper in the air. Each of these parts is structur- 

 ally best suited for vision in its respective medium. 



The larvae (fig. 13:21) are strictly aquatic. They 

 are long, slender, and have abdominal gills. 



Relationships. — Much has been written on the rela- 

 tionships of the Gyrinidae, and even among recent 

 authors there are wide differences of opinion. If 

 specialization for their mode of life (divided eyes; 

 short thick antennae, second segment with earlike 

 process; middle and hind legs as fanlike paddles) is 

 not overstressed, the gyrinids clearly belong in the 

 suborder Adephaga and to a caraboid stock. The larvae 

 have two free tarsal claws on each leg, a condition 

 not found outside the Adephaga. 



Respiration. — The adults take in air at a groove 

 just inside the posterior end of the lateral margin 

 of each elytron. It is stored in a dorsal reservoir 

 under the elytra, into which the abdominal spiracles 

 open. When a beetle dives, some of this air protrudes 

 as a bubble which glistens like quicksilver, and 

 which is held in place by the vestiture of the last 

 abdominal segment. In warm weather gyrinids go 

 beneath the surface only when frightened, or to lay 

 eggs, and do not stay under long. However, in regions 

 where winter forces them to hibernate they are said 

 to pass that time either buried in the bottom mud and 

 debris or clinging to submerged plants. Their air 



327 

 Leech and Chandler: Coleoptera 



reservoir presumably suffices during such a period 

 of low motabolic rate. 



The larvae (fig, 18:21) are independent of surface 

 air, since they have tracheal gills, a pair on each of 

 the first eight abdominal segments and two pairs on 

 the ninth, by which they obtain air directly from the 

 water. An undulant or trembling motion of (Ik 1 abdomen 

 provides the necessary current and movement of 

 water. The pupae are in mud colls (fig. 12:22</) above 

 the water, and breathe air in the regular manner. 



Life history. — In the north temperate zone winter is 

 passed in the adult stage, or perhaps in the larval in 

 some forms. Eggs are laid in the spring, attached 

 to Surfaces of the submerged parts of plants. They 

 are laid in rows or clusters and sometimes at a con- 

 siderable depth. Hatching takes place in from one to 

 three weeks. The young larvae drop to the bottom, 

 where they hide and hunt in the debris until nearly 

 full-grown. The larvae are predaceous and cannibalis- 

 tic, feeding on bloodworms, Odonata nymphs, and 

 even small fish, into which they inject a killing poison 

 through a canal in their slender curved mandibles. 



When mature, a larva of Gyrinus leaves the water 

 and either crawls up a suitable plant (Scirpus, Typha) 

 or onto some object at the water's edge. In the former 

 case it collects what adherent material it can scrape 

 from the surface of the reeds near the water line, 

 mixes in an adhesive substance, and places the mass 

 on its back. When it has enough it crawls up a stem, 

 shifts the load to the end of its abdomen, and while 

 in that position bends back and attaches the mass to 

 to the reed. It then bites a hole in the mass, works 

 its way in, closes the opening, and forms a pupal 

 cell within. A larva which goes to shore may collect 

 mud or sand and carry the load up a standing object, 

 or it may form its pupal cell under some shelter. The 

 larvae of Dineutus are said to build their cells around 

 them, a piece at a time, reaching to the ground each 

 time for the next load. 



Parasites. — The student is referred to the fine paper 

 by F. G. Butcher, 1933 (Hymenopterous parasites of 

 Gyrinidae with descriptions of new species of Hemi- 

 teles." Annals of the Entomological Society of 

 America, 26:76-85, incl. 1 pi.). Following is a list 

 of species reared from the cocoons of North American 

 Gyrinidae, and known to be primary parasites: 



Parasite 



Bathythrix gyrini 

 (Ashmead) 



Bathythrix pimplae 



Howard 

 Hemiteles cheboygan- 



ensis Butcher 

 Hemiteles hungerfordi 



Cushman 

 Eriplanus cushmani 



(Butcher) 

 Gyrinophagus dineutis 



(Ashmead) 



Host 



(this is the 



gyrinophagus 



of Butcher's 



Gyrinus sp. 



Hemiteles 



Cushman 



paper). 

 Gyrinus sp. 



Gyrinus sp. 



Gyrinus sp. 



Gyrinus sp. 



Dineutus assimilis, Gyri- 

 nus sp. 



