CHAPTER 13 



Aquatic Coleoptera 



By H. B. Leech and H. P. Chandler' 

 California Academy of Sciences, San Francisco 



The Aquatic Coleoptera are commonly termed "water 

 beetles." This is convenient and descriptive, but 

 does not imply close relationship among all the 

 included species. In the Nearctic region alone there 

 are ten families in which both larvae and adults of 

 virtually all species are aquatic, three in which at 

 least one stage is aquatic, two in which the larvae 

 occur in water or in the underwater parts of plants 

 and the adults are usually semiaquatic. These all 

 live in fresh (including mineralized and saline) or 

 land waters, in contrast to examples of five other 

 families (see Carabidae, Staphylinidae, Melyridae, 

 Eurystethidae, and Limnichidae) which are found in 

 the intertidal zone of the Pacific Coast sea beaches. 

 In addition there are many species which burrow in 



i wet mud and sand or hunt and hide under debris and 

 stones at the water's edge. These forms, and insects 

 which have merely fallen into the water are often 

 caught in collecting true aquatics. Hence, the com- 

 moner riparian groups are included in the following 

 keys to families. 



Sabrosky (1953) claims that some 277,000 species 

 of beetles were described from the world fauna by the 

 end of 1948. In the sense of the present study (but 

 excluding the terrestrial Ilydrophilidae) about 5,000 

 species are "aquatics." Some three hundred and thirty 



1 of these oc.cur in California, more than one-third of 

 them being Dytiscidae. Comparatively little collecting 

 has been done here as yet, and there are undoubtedly 



I many undescribed species of water beetles. 



The Nearctic water beetles represent two of the 



! three currently recognized suborders of Coleoptera. 

 The families Amphizoidae, Haliplidae, Dytiscidae, 



1 Noteridae, and Gyrinidae belong to the Adephaga; the 

 remainder to the Polyphaga. Adults of the aquatic 

 Adephaga carry an air supply under the elytra, and 



1 when returning to the surface to renew it, break the 

 surface film with the tips of the elytra and abdomen; 



All the keys to larvae, except that for Helodidae, are to be 

 credited to the late Harry P. Chandler. He also wrote the texts 

 for the families Limnichidae, Psephenidae, Dryopidae, Elmidae, 

 Ptilodactylidae, Chrysomelidae, and Curculionidae. The re- 

 mainder of the article was written by Hugh B. Leech. 



the underside of the body is virtually hairless. The 

 aquatic Polyphaga also carry air between the elytra 

 and abdomen, but in addition almost all of them have 

 the underside of the body covered with a short, dense 

 hydrofuge pubescence. This holds a sheet of air, 

 which is in connection with the elytral reservoirs. 

 When coming up to renew their supply, hydrophiloid 

 beetles break the surface film with an antenna. 



The mature larvae of virtually all aquatic beetles 

 leave the water to form their pupal cells. Exceptions 

 include those which pupate in gas-filled cocoons 

 (Noterus of Noteridae, Donacia, and Neohaemonia of 

 Chrysomelidae, Lissorhoptrus of Curculionidae); and 

 the genus Psephenoides of Psephenidae, which nor- 

 mally has the water actually in contact with the pupal 

 cuticle. 



Details of relationships of the various families, 

 methods of respiration, life histories, habitats, and 

 distribution will be discussed separately for each 

 family. All Nearctic families having one or more 

 aquatic or semiaquatic species are included except 

 Chelonariidae, the larvae of which are said to be 

 semiaquatic, but are unknown to us in nature. 



Fossil water beetles. — The first undoubted Coleo- 

 ptera fossils are from the Upper Permian, of about 

 200 million years ago. Some elytra of this age, from 

 Australia, appear to be of beetles related to the 

 modern family Ilydrophilidae. What appear to be dytis- 

 cid types occur in the Upper Jurassic, and Hatch 

 refers one Liassic or Lower Jurassic fossil definitely 

 to the Gyrinidae. Specimens which can be referred to 

 modern genera date from about Eocene time, the period 

 preceding the Oligocene of Baltic Amber fame. 



Sixty-eight species of fossil aquatic or semiaquatic 

 water beetles have been described from North America: 

 Dytiscidae (25), Gyrinidae (2), Hydrophilidae (25), 

 Psephenidae (3), Chelonariidae (1), Limnichidae (1), 

 Dryopidae (2), Helodidae (1), Chrysomelidae (8). The 

 Hydrophilidae are largely Eocene and Miocene, with 

 a few from the Pleistocene; the Dytiscidae are pre- 

 dominantly Pleistocene, with some from the Miocene; 

 species of the other families are from the Miocene, 

 except the Chrysomelidae (Donacia) which are Pleis- 



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