208 FIELD ZOOLOGY. 



color suffuses the whole wing. In the damsel flies these 

 colorations are often bright green, blue, or red. The 

 iridescent gleam from the wings of a living dragon fly is 

 probably due to the refraction of sunlight from the 

 minute blood drops mingled with air, as this fluid circu- 

 lates through the delicate double sac forming the wing, thus 

 refracting the light components of different length, giving 

 corresponding color impressions. These colors fade in 

 death and the wing seems uniformly colored or colorless. 



The wing movement in flight is a figure eight per- 

 formed by the wings acting separately. These are the 

 insects which have the tracheal pockets reinforcing the 

 usual tracheary tubes of the respiratory system. They 

 do not fly so high as do some of the butterflies; nor do 

 they make migrations as do some of the lepidopters, but 

 their flight is much stronger, they can go much longer on 

 the wing, and they hunt their prey exclusively from on 

 the wing. The Odonata, both immature and adults, 

 have strong mandibles and maxillse for seizing their prey 

 and tearing its flesh in pieces. 



The head is unusually large, more than two-thirds 

 of it being made up of the compound eyes. There are 

 more than thirty thousand facets in the compound eye 

 of a dragon fly; that means more than thirty thousand 

 parts in the mosaic of yourself when the dragon fly looks 

 at you. And with the Odonata as with the Lepidoptera, 

 the finer the mosaic, the better the image. Indeed you 

 will find it very difficult to catch a dragon fly off its guard. 

 You may be obliged to steal upon it from behind, and then 

 feel ashamed for killing an insect so intelligent and so 

 beneficial in every way. Dragon flies have a special 

 fondness for flies and mosquitoes, and they also devour 

 wasps. If you are ever sneaking enough to catch one late 



