CONSPICUOUS INSECTS OF SUMMER-TIME 



261 



injurious. The grub lives within the 

 trunks of trees, feeding on the tissues of 

 the wood, and takes at least three or 

 four years to complete its development. 



Having glanced at the largest of 

 British land beetles, we may conclude 

 by a brief consideration of the largest 

 species of the Britisli \\'ater or Di\ing 

 Beetles. 



The photograph below shows a pvLir 

 of these beetles (Dyiiscus marginalis). 

 To see some of the beetles in the living 

 state is an eas}' matter. On the surface 

 of a pond a number of objects may be 

 seen floating like little corks ; throw 

 a stone into the water and instantly every 

 one of them disappears. Wait for a 

 while and remain quiet, however, and the 

 objects will, one after another, come 

 back to the surface again, simpl}'^ because 

 they are compelled to do so. They are 

 Water or Diving Beetles such as those 

 shown in the photograph, or nearly 

 related species, and as they are air- 

 breathers they must come to the surface 

 as soon as their air supply is exhausted. 

 So they float upwards and poke out of 

 the water the tail ends of their bodies 

 to breathe ; not that the insects breathe 

 through their tails, but in that position 

 they can take in air under their horny 

 wing-covers. The air is then in contact 

 with a series of little holes called 

 " spiracles " arranged along each side of 



their bodies, and it is through these holes 

 that the beetles breathe. Indeed they 

 breathe just as other insects do, for in- 

 sects do not respire through their mouths ; 

 even on the body of a caterpillar a row of 

 S]:)iracles will be found on both sides of 

 tlie body. Thus the beetles become, 

 as it were, diving bells. Xow, a little 

 observation of this kind not only teaches 

 how this insect breathes, but, if it be 

 desired to make a capture, it will be 

 obvious that, by waiting until the beetle 

 nears the surface of the water, a sudden 

 swoop with the water-net at that moment 

 will most probably be successful, as the 

 insect cannot return to the depths if its 

 air supply is e.xhausted. The insects, 

 however, are remarkably quick, and their 

 capture is not easy ; a better way to secure 

 them is to drag in the water-weeds and 

 search amongst them. Their wings are 

 large, and as evening approaches the 

 beetles climb the stems of water-plants to 

 expand them. In this way they reach 

 new ponds and seek their mates ; some- 

 times, too, as daylight approaches they 

 are in such a hurry to get back to their 

 aquatic surroundings before their daylight 

 enemies get abroad, that they not infre- 

 quently allow themselves to drop like 

 stones upon the roofs of greenhouses and 

 similar places, which from above they 

 have doubtless mistaken, in the twilight, 

 for a sheet of water. 



JoHx J. Ward. 



MALE AND FEMALE WATER OR DIVING BEETLES. 

 The male is on the left. 



