THE LIFE-HISTORY OF HYDROBIUS FUSCIPES, L. 335 



water, head downwards, on the side of the tumbler, and with the jaws widely expanded. 

 Under natural conditions it may be found in a similar position on projecting water 

 plants, or it is often to be seen enveloped in spirogyra with only its head projecting out. 

 Its food consists largely of Entomostraca, daphnids being the chief item, though it also 

 attacks small insect larvae and is quite ready to devour one of its own kind. 



The prey sooner or later comes within reach of the jaws and is at once seized. The 

 larva then rapidly wriggles backwards out of the water, and having once got to a fairly 

 dry spot, it raises its head and thoracic segments off the substratum and, holding the 

 prey with antennae, maxillae, and labium, it proceeds to puncture it through and through 

 by opening and closing the jaws, turning the captive round and round by movements 

 of the antennae and maxillae. The outwardly projecting points on the upper surface of 

 the submentum and the row of small spines on. the cardo of the maxilla assist in holding 

 the prey and prevent the solid parts from being sucked down, as only the juices, with a 

 large quantity of air, are absorbed. When there is nothing left but a crumpled mass of 

 solid substance the larva lays this down beside it and either rests for a while or returns 

 to the water in search of more food. It is apparently absolutely essential that the 

 larva should get at least its head out of the water for feeding. By preventing larvae 

 from so doing I found that they died in spite of being in the midst of daphnids. They 

 would seize one and carry it about for quite a long time, always endeavouring to get out 

 of the water. 



Quite recently I discovered a larva with its head buried in an egg-cocoon devouring 

 a batch of fresh-laid eggs, but whether this is a usual occurrence or was a special 

 discovery on the part of this individual I do not know. The cocoon was floating on 

 the water, but I imagine that the eggs must have been submerged by the time the larva 

 had penetrated the wall of the cocoon. 



The larvae seem to spend a great deal of their time out of water. I have often found 

 them on the muddy sides of ponds, where they must be largely devoured by small birds 

 and in the tumblers they were constantly to be seen on the sides. I have seen them 

 seizing one of their own kind when out of water, but as a rule they return to the water 

 for their food, and if they wander too far from it they are apt to suffer from drought. 



The duration of the first larval stage varies considerably. In specimens hatched in 

 the middle of April the usual time until the first moult was about fifteen days, but later 

 on, in warmer weather, the first stage only lasted from six to ten days. A second 

 moult takes place at the end of a period about as long as the first. The two moults 

 have, as far as external characters are concerned, produced no change in the appearance 

 of the larva. In the young larva the head and jaws are much larger in proportion to 

 the body than they are in the older larva, but this change is merely due to a more 

 rapid growth of the body as compared with that of the head and is not connected 

 with the moults. 



Having moulted twice the larva is in its last stage, and this occupies five to seven 

 or even eight weeks. At the end of that time the full-grown larva crawls out of the 



