Dragon-flies

(Order Odonata.)

Excepting the butterflies, there are few more attractive and graceful insects than the "dragon-flies," as the members of this order are generally termed. They are insects which have always attracted attention, and which are known by a variety of vernacular names, of which dragon-fly is the commonest English term. They are known in some parts of the country as "devil's darning needles;" elsewhere as "snake feeders" or "snake doctors;" in Scotland as "flying adders," and in some parts of England as "horse stingers." Although the insects are perfectly harmless, these names well indicate the existence of numerous popular superstitions. Some believe that they will sew up the ears of bad boys; others that they sting horses; still others that they act as feeders and physicians to snakes, especially to water snakes.

The Odonata are slender insects with a very large head which moves most easily upon its slender neck, even rotating to a considerable extent. The eyes are very large, but the antennae are small and short. The wings are elongate, nearly equal in size, and have many veins, both longitudinal and transverse, so that the entire surface of the wing is cut up into many small cells. The legs are placed near the front of the thorax, and all curve forward and are used for grasping the prey of the dragon-fly, and never for walking. In fact, the legs are unfitted for walking, although they are used to grasp the twig or other object upon which the dragon-fly may rest. All of the dragon-flies are aquatic in their early stages. The metamorphosis is complete in so far that the larvae differ radically in appearance from the adults, but the pupa is not quiescent at any time. It is very active, and feeds up to the moment when the final metamorphosis begins. The jaws in all stages are strong, and both larvae and adults are extremely active and are among the strongest and most graceful flyers of all insects. Their flight is so perfect that it has been seriously suggested that flying machines should be modeled after the flight mechanism of these insects.

A very peculiar feature of the adult is the curious separation in the male of the intromittent organs from the opening of the ejaculatory duct. The former are placed on the under side of the second abdominal segment, while the latter are on the next to the last ventral plate. Therefore, before copulation, the male curves his abdomen around beneath, so that the ninth segment of the abdomen is brought into contact with the second, thus transferring the fertilizing fluid to the intromittent organ. The tip of the abdomen of the female is bent around and joins with the under side of the second segment of the male's abdomen, the male frequently grasping the female around the neck with certain appendages at the extremity of his abdomen. He retains this hold after fertilization, and frequently during the entire process of egg-laying. Even with such species as descend under the surface of the water to lay their eggs the male has been observed to still retain his grasp of the female's neck, and to be carried down under the water with her.

Dragon-flies capture their prey on the wing, and feed upon almost all flying insects, especially the small ones--that is, the gnats and midges. They alter their direction with perfect facility, and dart here and there, unerringly capturing their prey. Possibly some of the smallest are seized with the jaws, but the larger ones are undoubtedly captured by the legs, and are consumed during flight, and so rapidly is all this done that it is practically impossible to see the operation. The only way, in fact, that one can know that an insect has been captured is, as Dr. Needham expresses it, to see that the place that once knew them knows them no more.

Flies seem to be their commonest food, but large dragon-flies will eat small ones. Leaf-hoppers and even small butterflies and moths are captured by them. Some forms will occasionally pick up a moth from a weed or a grass stem on which it is resting, and even one of the large swallow-tailed butterflies has been seen captured by a dragon-fly, while Williamson states that he once saw one holding a large wasp in its jaws. The voracity of a large dragon-fly may easily be tested by capturing one and holding it by its wings folded together over its back, and then feeding it live house-flies. I should hesitate to say how many it will accept and devour, as I never tried one to the limit of its capacity. Beutenmuller found that one of the large ones would eat forty house-flies inside of two hours, while a smaller one ate twenty-five in the same time. It is an odd fact that a dragon-fly will eat its own body when offered to him. Even when insufficiently chloroformed and pinned, if one revives, it will cease all efforts to escape if fed with house-flies, the satisfying of its appetite making it apparently oblivious to the discomfort or possible pain of a big pin through its thorax. There is one record to the effect that a dragon-fly has been observed feeding upon the flesh of a dead reptile.