THE LIFE-HISTORY OF HYDROBIUS FUSCIPES, L. 337 



that the pupae may lie dormant through the winter, or possibly the imago may emerge 

 from the pupal skin in the autumn and remain within the cell until the spring. Under 

 ordinary circumstances the beetle remains some time within the cell before breaking out, 

 but a newly emerged beetle is always recognisable on account of its comparative soft- 

 ness, and I have no record of having found newly hatched imagines before June. 



Whereas a large number, perhaps all of the Dytiscida3, pass the winter in the larval 

 as well as in the imago condition, I think that normally the Hydrophilidse are then only 

 imagines, and that they all usually complete their life-cycle within a single season. 

 This certainly is generally the case with Hydrophilus and, I think, with Philhydrus 

 maritimus, Thorns, and, were it not for Miall's statement, I should also include Hydro- 

 bius fuscipes, L. 



Fecundity. 



The egg-laying period of a single female apparently continues through the egg- 

 laying period of the species. I have isolated a number of females from the time they 

 built their first cocoon, and up to the end of June some have built as many as seven 

 egg-cocoons. In these cases no male has been with the females since they started their 

 first cocoon, with one or two exceptions, in which they received a $ after the completion 

 of the first cocoon. The average number of eggs in these later cocoons is rather smaller 

 than in the earlier ones, there being only about twelve ; but each of these females has 

 produced from eighty to a hundred eggs up to the end of June, and there may yet be 

 one or two cocoons built by them before the end of the season. The eggs are fertile, 

 the development of the embryos being quite normal. 



Hydrobius fuscipes is certainly a common species, but there must be a tremendous 

 mortality among the larva?. 



Summary. 



Hydrobius fuscipes, L., is a common water-bettle of which H. picicrus, Thorns, is 

 apparently only a variety, the two forms being extremes of a series and tending to prefer 

 different environments. 



The food of the imago is chiefly filamentous and confervoid algse, but it also 

 devours dead insects, etc. The jaws, as in all the Hydrophilidse, have grinding 

 surfaces at their bases, but the two jaws differ from one another in accordance with slight 

 differences in function. 



The courtship of Hydrobius is peculiar, the male on the back of the female bending 

 forward over her head and tapping upon her labium with his palpi. There are 

 apparently only certain times at which a female will accept a male. The peculiar 

 twisting of the penis in the process of copulation, which was observed in Hydrophilus 

 by Donisthorpe, is also seen in Hydrobius. 



