INSECTA: COLEOPTERA 



247 



The Pupa. 



The segmented body narrows down towards its eleventh 

 and last segment, and bears terminally two fringed appendages 

 (Fig. 173, t). When the larva floats up to the surface, with 

 its tail upcurved as in Fig. 173, in order to take in a fresh 

 supply of air through the two spiracles at the tip of the 

 tail, these hairy appendages float out on the surface film 

 and help to buoy up the body. Seven other pairs of spiracles 

 are present down the sides, but they are closed. After having 

 drawn in sufficient air, the larva, with a few vigorous strokes 

 of the tail, swims down, and seizes the weeds with its jointed 

 thoracic legs, and there lies in wait for its prey. 



Late in the summer the larva leaves the water, 

 and pupates in the damp earth near. It first 

 excavates a little cell, then sheds its skin, and the pupa is 

 displayed. This stage may last only a week or two if it is 

 reached fairly early in the summer, but if late, the perfect 

 insect will not emerge until the following spring. When first 

 the pupal skin is discarded, the beetle is white and soft, and 

 it is not until after some 

 days that its skin turns 

 brown and hard, and it takes 

 its first flight into the air. 



Other Water Beetles allied 

 to Dyticus. 



Acilius. 



FIG . 174. A cilius sulcatus. 



The first pair of legs is hidden below the 

 body. 



Another very 

 common water 

 beetle closely allied to Dyti- 

 cus is Acilius sulcatus, the 

 " furrowed " Acilius. It is 

 smaller than Dylicus, being 

 not more than f of an inch 

 long, and it has a very flat 

 body, greyish-brown above and darker underneath. It has 

 peculiar black markings on the head and thorax (Fig. 174), 

 and also some dusky spots near the hind end of the elytra. 

 The sides of the abdomen may be spotted with yellow. As 

 in Dyticus, the male has an enlarged disc on each of the 

 front pair of legs, though these are usually carried tucked 

 away under the body, and are therefore difficult to see ; if, 



