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Leech and Chandler: Coleoptera 



I k 



Fig. 13:7. Dytiscidae, structures of adults, a, Agabus bifarlus, reduced and fully developed 

 wings; b, Cybister explanaius, adult, showing scutellum; c, Dyfi'scus sp., head showing non- 

 emarginate eyes; d, Hydroporus sp., front tarsus showing very small fourth segment; e, Bidessus 

 sp., showing trochanter (tr) of hind leg of adult free, not covered by hind coxal process; f, Aga- 

 bus sp., head of adult to show emarginate eyes; g, Dytiscus sp., front tarsus of male; h, Hygrotus 

 sp., showing trochanters (tr) of hind legs covered at base by lobes of hind coxal processes; i,j,k, 

 Hydroporus spp., posterior margin of hind coxal process showing variation of this structure within 

 the genus; /, Rhantus sp., front tarsus of male (a, Leech, 1942; b. Leech, 1948; c,f, F. Balfour- 

 Browne, 1950; d,e,h, F. Balfour- Browne, 1940; g, Miall, 1903; f-fc, Guignot, 1950; /, Williams, 

 1936). 



Waters which have had but few beetles may become 

 populous for a time during the spring and fall migration 

 flights, usually May and September. Very little is 

 known about the flight habits of our species, or indeed 

 even about which ones can fly. Leech (1942) dis- 

 cussed dimorphism in the wings (fig. 13:7a) of Agabus 

 bifarius (Kirby), a species which often occurs in 

 ephemeral ponds. As late as 1948. Brinck was able 

 to cite only six species of dytiscids in which the 

 wings were known to be reduced. But in 1950 and 

 1952 Jackson, working in Scotland, opened up a 

 whole field for study; she found by dissection that 



many species which had fully developed wings had 

 atrophied flight muscles, and were in fact flightless. 

 However, not all examples of some species, or even 

 all specimens from a single pond, had the same 

 development of flight muscles. In other cases it 

 seemed that the muscles were functional for a short 

 time after the beetles emerged from their pupal cells, 

 then gradually atrophied. It is interesting to compare 

 this with the case of some solitary large queen ants. 

 Richards (1953:137) says that after a nuptial flight 

 and loss of her wings, such a queen ". . . hunts for 

 a crevice or digs a small cell under a stone. Here 



