754 Mr. Frank Balfour Browne [May 9, 



WEEKLY EVENING MEETING, 



Friday, May 9, 1913. 



His Geace The Duke of Northumberland, E.G. P.C. 

 D.C.L. F.R.S., President, in the Chair. 



Frank Balfour Browne, Esq. M.A. (Oxon.), F.R.S.E. F.Z.S. 



The Life-History of a Water-Beetle. 



The life-history of a water-beetle can be outlined in a very few 

 words. An egg is laid by the mother-beetle : an aquatic larva hatches 

 out which feeds and grows, and, during the process of growth, moults 

 several times. AYhen full grown it leaves the water and burrows into 

 the earth, forming a " cell," in which it changes to a pupa. After a 

 time the pupal skin is cast off, and the perfect insect makes its way 

 out of the cell and resumes its life in the water. 



There are, however, all sorts of interesting details in the life- 

 history, and these details often differ considerably in different types. 

 There are differences in the egg-laying habits ; differences in the 

 method of development of the embryo ; differences in the way the 

 larva gets out of the egg ; differences in the way it feeds and in 

 the nature of its food, and so on ; and it is these differences which 

 are of importance to each species in enabling it to fit in among other 

 species in the life of the community. 



Although there are a number of widely separated species of 

 beetles which inhabit the water, there are two groups which are 

 usually referred to as " water-beetles," and these may be broadly 

 distinguished as the swimming carnivorous group — the Hydradephaga 

 — and the creeping herbivorous group — the Falpicornia, or Hydro- 

 philidse. The descrijjtion of this second group is not strictly accurate, 

 as the larvffi are, apparently without exception, carnivorous, and the 

 perfect insects, althougli capable of subsisting upon a vegetable diet, 

 in at least many cases enjoy animal food ; and although they are 

 somewhat differently constructed from the swimming water-beetles, 

 some of them are very fair swimmers. 



I propose to outline the life-history of a type of the Hydradephaga, 

 and then to compare with it a type of the Falpicojmia ; and as a type 

 of the former group 1 will describe a species of Dytiscus, D. lapponicus, 

 whose life-history I worked out during last summer. 



Tlie male and female differ in general appearance, the former 

 having smooth wing-cases, the latter having these grooved or fluted. 

 The male has also a pad on each of the front legs, while the female 



