,28 BAKER : HYDROBIUS FUSCIPES. 3 



vegetarian in a state of nature I am unable to say, but on dissecting 

 tank-reared specimens I have found small crustaceans, such as 

 Cypris, inside their oesophagus , but it is hard to imagine how such 

 lively little creatures as these can be obtained in any abundance by 

 such, comparatively speaking, slow-moving insects as Hydrobius. 

 Whatever the cause, however, it is an undisputable fact that the 

 further north one gets, the smaller are the Hydrobii, and one 

 specimen I got at Sledmere only measured barely 5 mm. in length. 



In colour the beetle varies from light brown (in recently hatched 

 specimens) up to a very dark brown or even black. This, however, 

 is subject to variation, for many of the Hydrobii which inhabit ponds 

 or ditches near to the coast show a tendency to a metallic blue tint. 

 This I noticed more especially in the ponds on the banks of the 

 Humber to the east of Hull, and also in a pond on the sand dunes 

 near to Cleethorpes. 



Generally speaking, it is a typically vegetarian beetle, and, 

 wherever a weed-grown pond is found, there you may be sure to 

 find our friend, generally accompanied by a companion of like 

 habits, Htlophonis aquaticus. No matter if the pond be covered 

 with a continuous covering of duck-weed, stretching from bank to 

 bank, a few minutes' search will, as a rule, discover one, if not both, 

 of these creatures. In fact, it is in such ponds as these that they 

 thrive best and occur in the greatest numbers, for their great 

 enemies, the carnivorous aquatic beetles of the family Dytiscidce 

 do not, as a rule, frequent ponds in which there are no open 

 spaces where they can easily come to the surface to breathe, and 

 consequently they are not so much ' thinned.' Other enemies of 

 theirs there are, however, in abundance, including all such birds 

 as ducks, teal, and water-hens, and last, but not least, frogs and 

 newts are responsible for numbers of them. Their sluggish habits 

 and slow mode of locomotion place them in a very great measiire at 

 the mercy of these numerous enemies. 



Their legs are formed more for climbing along the stems and 

 leaves of water-plants than for swimming, but they can, by rapidly 

 working their legs, proceed at a fair pace through the water. As 

 a rule, they turn over on their backs when they wish to swim, for 

 two reasons. In the first place, being lighter than water, their whole 

 body is not immersed, and the smooth surface of the dorsal portion 

 offers much less resistance to the water than the ventral surface, 

 which is thickly clothed with hairs. The second reason is connected 

 with their respiratory system. In most aquatic beetles the air 

 necessary for the purpose of respiration is stored between the elytra 

 and the dorsal surface of the abdomen, the beetle elevating the tips 



Nov. 1894. 



