COLEOPTERA 483 



The females deposit their eggs singly in punctures in the tissues 

 of living plants. The 

 larvas are known as 

 water-tigers, because 

 of their blood-thirsti- 

 ness. They are elon- 

 gated, spindle-form Fig. 568. 

 grubs (Fig. 568). The 



head is large, oval or roimded, and flattened; the mandibles are large 

 and sickle-shaped; in each there is a slit-like opening near the tip; 

 from this opening a canal leads along the inner surface to a basal 

 opening on the upper surface, which commimicates with the corner 

 of the mouth when the mandible is closed. The central part of the 

 mouth, between the mandibles, is closed, the upper and lower lips 

 being locked together by a dovetail joint. The mandibles are ad- 

 mirably fitted for holding prey and at the same time sucking juices 

 from its body. The thorax is furnished with six well-developed legs. 

 The abdomen is terminated by a pair of processes ; at the tip of the 

 abdomen there is a pair of large spiracles, which the larva protrudes 

 into the air at intervals, in order to breathe. 



When a larva is fully grown it leaves the water, burrows into the 

 ground, and makes a round cell, within which it imdergoes its trans- 

 formations. The pupa state lasts about three weeks in summer; 

 but the larvas that transform in autumn remain in the pupa state 

 all winter. 



This is the largest of the families of water-beetles; more than 

 three hundred North American species are known. 



The best way to obtain specimens is to sweep the vegetation grow- 

 ing on the bottom of a quiet pool with a dip-net. 



The larger of our common species belong to Cyhtster, Dyttscus, 

 and allied genera. In Cyhister the little cups on 

 the under side of the tarsal disks of the male are 

 similar, and arranged in four rows. In Dyttscus 

 and its allies the cups of the tarsal disks vary in 

 size. Figure 569 represents a common species of 

 Dyttscus. 



The most common of the diving-beetles which 

 are of medium size belong to the genus Acllius. In 

 this genus the elytra are densely pimctured with 

 very fine punctures, and the females usually have 

 Fig. 569- four furrows in each wing-cover (Fig. 567). 



There are also common diving-beetles which are 

 of about the same size as the preceding, but which have the wing- 

 covers marked with numerous very fine transverse strias; these be- 

 long to the genus Colymbetes. 



Of the smaller diving-beetles, measuring less than 6 mm. in length, 

 many species can be foimd in almost any pond. These represent 

 many genera. 



