32 INJURIOUS AND USEFUL INSECTS 



the leaves and blossoms of roses and fruit-trees. The beetle 

 is only half the length of the cockchafer. It has rusty wing- 

 covers, and a dark green head and thorax. 



6. A CARNIVOROUS WATER-BEETLE 

 {Dytiscus matgiaalis) 



The young naturalist, issuing forth with jam-pot and home- 

 made net to capture the living creatures of the ponds and 

 ditches, is likely to bring back insects of the Dytiscus-family, 

 together with the minnows, caddis-worms, and water-snails 

 with which he hopes to start his first aquarium. He will 

 perhaps notice that the water-beetles of this family are 

 excellent swimmers ; that they are of a flattened shape, 

 which enables them to glide without unnecessary resistance 

 through the water, and to penetrate narrow recesses ; that 

 their outline is oval, head, thorax, and wing-covers being 

 rounded off to an unbroken curve ; that their colours are 

 brown and black ; and that they are of various sizes, from 

 which he will probably draw the mistaken conclusion that 

 the small ones are the young, and the big ones the full-grown 

 beetles. A short experience of the behaviour of the beetles 

 when tumbled into a bowl of water with fishes, snails, and 

 miscellaneous water-insects will lead him to suspect, or 

 to know for certain, that the Dytiscus-family is eminently car- 

 nivorous, attacking and often devouring their fellow-prisoners 

 of all grades. A wider experience will teach our young col- 

 lector that the water-beetles have wings and can use them. 

 He will further come to know that an insect of any kind 

 which has wings is always adult. Its growth has been com- 

 pleted in the larval and pupal stages, and the imago, or 

 winged insect, neither grows nor changes its skin. The small 

 beetles will never grow into big ones : their size, like their 

 form and colour, are fixed characters of the species to which 

 they belong. 



The large species of Dytiscus, which is called Dytiscus mar- 

 ginahs, takes its name from the yellow stripe which runs round 

 the whole body on its upper surface. Remark its firm and 

 polished integument, the unbroken contour, and the angulation 

 of the under side of the abdomen along the middle line. 



