NERVE-WINGED OR LACE-WINGED INSECTS 297 



NERVE-WINGED OR LACE-WINGED INSECTS, OR DRAGON-FLIES AND THEIR RELATIVES 



By THE REV. TllKOnORK WOOD, F.E.S. 



The Nerve-winged Insects owe their title to the pecuHar character of their wings, the horny 

 veins which form the framework of those organs being multipHed and siib-di\ided to such an 

 extent that they assume the appearance of exceedingly delicate network. 



These insects fall naturally into two great groups, in one of which the chrysalis, or pupa, is 

 active, and continues to take food like the grub, while in the other it is passive and helpless, like 

 that of a butterfly or a moth. 



Prominent among the members of the first division are the Dragon-flies, which owe their 

 title partly to their extreme voracity, and partly to the fact that they feed entirely upon living 

 insects, which they pursue through the air. Thc\' are exceedingly swift of wing, and maj- 

 be seen hawking over ponds and streams on an)- tine day throughout the summer and early 

 autumn. 



The earlier part of their lives is spent in the water, in which the eggs are laid by the 

 parent insect. The grubs are usually of a dull grey or brownish-green colour, and are remark- 

 able for a curious organ known as the " mask," 

 which partly covers the lower surface of the 

 head. This apparatus consists of two joints, 

 which fold upon one another, but can be ex- 

 tended at will, the one farthest from the head 

 terminating in a pair of large and powerful 

 jaws. When the grub perceives an insect- 

 victim, it swims cautiously beneath, and seizes 

 it by means of these jaws. The " mask " is 

 then folded, and the prisoner drawn down 

 within reach of the mandibles, by means of 

 which it is speedil}' de\-oured. 



The method of swimming practised by 

 the dragon-fly grub is also very curious. 

 Through the centre of the body runs a 

 longitudinal tube, terminating in a circular 

 orifice, closed by means of five tightly fitting 

 vah'es. These valves, which together form a 

 •sharp spike when closed, can be separated at 

 ■will. When the insect wishes to swim, it 

 fills the tube with water, and then squirts 

 the contents forcibly out, the result being 

 that it is driven swiftly forwards by the 

 Teaction. 



The pupa of the dragon-fly is very much like the grub, with the exception that the 

 rudiments of the future wings may be seen on the back. 



About forty species of these insects are found in the British Islands, of which the Gre.VT 

 Drac.OX-FLY is a well-known example. The body is 3 inches in length, while the extended 

 wings measure about 4 inches from tip to tip. In colour it is light rusty brown, with a 

 few pale markings. The " Horse-stin(;er " — which is perfectly harmless, notwithstanding its 

 popular title — is also common, and may be recognised at once by its flat dull \'ellow body, 

 which becomes blue in the fully developed male. In the graceful and beautiful DemoioELLE 

 the male is deep blue, with black patches on the wings, while the female is entirely green. 



Allied to these insects is the Common M.W-FLV, popularly supposed to li\-e for one day 

 only. As a matter of fact, however, it spends a couple of \-ears in the grub and pupa states, 

 inhabiting burrows in the banks of ponds and streams. These burrows are cur\'ed, and have 



Ph,:, by «'. p. Ddnd,, F.Z.S. 



DRAGON-FLY 



Theie insecfs are often knoivn as ^^ Horse-itin^ers^''* although the^ da 



not iting horses ; in Jacty they are perfectls harmleis^ except 



to insects smaller and iveaker than themselnjes 



