22 NEW ZEALAND ENTOMOLOGY. 



smaller. Twenty-one closely allied insects belonging to 

 two genera are described by Captain Broun in his Manual,. 

 the largest being PterosticJms australasicz, which is found 

 in similar localities to the present species, but is not so 

 common. 



Group HYDRADEPHAGA. 

 Family Dyticid^:. 

 Colymbetes rufimanus (Plate I., fig. 4, 4a larva). 

 This insect is found plentifully in all still waters during 

 the summer months. Its larva is a soft elongate grub, 

 provided with six slender thoracic legs, and a pair of 

 powerful mandibles. The posterior extremity of the body 

 is furnished with two curious appendages bearing a spiracle 

 at the apex of each, which the larva frequently protrudes 

 above the surface of the water. The air is taken in through 

 the spiracles, and conveyed to all parts of the body by two 

 main air-tubes, one of which springs from each spiracle, and 

 branches throughout the insect in every direction. During 

 the spring months the larvae may be found of various sizes 

 in similar situations to the imago ; they are very voracious,, 

 devouring freshwater shrimps, Ephemera larvae, and occa- 

 sionally, when pressed by hunger, they will even destroy 

 individuals of their own species for food. These they 

 capture by means of their powerful mandibles, retaining a 

 firm hold of the victim until they have consumed all the 

 fleshy portions, the rest of the carcase being thrown aside, 

 and a fresh search made for more. One individual I kept 

 for some time, remained perpetually concealed in a small 

 patch of green weed, growing in the middle of its aquarium. 

 In a short time it became surrounded with the skeletons 

 of small water shrimps which had been seized by the 

 larva as they passed by its hiding place, the unfortunate 

 crustaceans only discovering their enemy when it was 

 too late. I have not yet observed the pupa of this 



