DRAGON-FLY, an order of insects, the Odonata, allied the may-flies and ephemerids, with long, slender bodies, very large mobile heads, immense eyes, short antenna, and two pairs of long, nearly equal wings of 'a firm and glossy texture, and closely netted with many veins. The mandibles are powerful, the mouth-parts being so fused and solidified as to form a most effective trap for catching the small insects upon which dragon-flies feed. The prothorax is small, the meta-thorax and meso-thorax large, and the meso-thorax slopes over the meta-thorax, by which arrange ment the spinous legs are thrust forward, so that they project under the head. These legs are unfitted, and are never used, for walking; but as instruments for catching and holding prey or for clinging to plants. The hind body is proportionately longer than in any other group of insects; it has 10 evident segments, the hindmost carrying a pair of stiff unjointed cercopods. The male genital armor is situated on the second abdominal segment — a position unknown in any other insect; and the intromit tent organs are separate from the ejaculatory ducts, the latter being near the extremity of the abdomen. °Therefore,° as Howard explains, °before copulation the male curves his abdomen around beneath, so that the ninth segment of the abdomen is brought into contact with the sec ond, thus transferring the fertilizing fluid to the intromittent organ. The tip of the abdomen of the female is bent around and joins with the underside 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. This compli cated embrace commonly observable where these flies are numerous in midsummer, once obtained is likely to be held during the whole process of egg-laying, even in many cases when the deposition takes place under water.
Dragon-flies are semi-aquatic in all their life and habits. The eggs are laid in the stems bf submerged plants by some species, which are provided with an instrument for cutting through the bark, each egg being pushed into the cutting as the female moves down the stem. As a rule, however, the eggs are dropped into the water, or washed off by dipping the tip of the abdomen. The number of eggs laid is large, exceeding 100,000 in the case of many libellulids.
When the eggs hatch the young immediately begin a life of activity and depredation. Molts follow one another rapidly, and the first larval form soon changes into a °nymph,° a form equivalent to the pupa stage of other insects, but differing in the fact that activity continues. These young remain under water, have short, broad hinder bodies, walking legs, feelers, and breathe by means of °rectal gills.° They prey upon everything edible, including their own weaker brethren. To assist them in doing this the mouth-parts are modified into an insect catching trap, forming an innocent-looking mask, within which are concealed grasping organs, ready to be shot out when an unsus pecting 'little animal creeps too near and the mask is suddenly lifted. When the broad and
flattened nymph has become full-grown it crawls out of the water upon some warm rock, where presently its skin splits open and the adult dragon-fly emerges. These changes are easily studied'by breeding dragon-flies in an aquarium.
The voracity of dragon-flies is notorious. They seize and devour all sorts of insects, in chiding smaller species of their own race, and sometimes moths, butterflies and wasps. Flies form their principal fare, however, and they consume vast quantities of house-flies and mosquitoes, but their service in killing the latter pests is mainly done during the larval stages. They abound, in midsummer, in most parts of the world, and sometimes appear in enormous swarms, millions moving across the country in company; such swarms are the result of various local conditions and are not migrations, properly speaking. The great beauty which most of the species have, glittering in metallic hues and skimming through the sunshine on brilliant, gauzy wings, has made them objects of univer sal admiration; but this admiration is strangely coupled with a popular fear and superstition toward them. Thus they are commonly known among American children as °devil's clarniing and are accused of an intention to sew up the ears of bad boys, or work mischief in the hair of naughty girls. The negroes of the Southern States call them "snake-doctors,* and say they feed and nurse ailing serpents. In Great Britain, they are known as °horse 'flying-adders* or and are believed to carry a poisonous sting in their tails. All these superstitions are calum nies upon a harmless and beneficial insect.
About 2,000 species of dragon-flies have been described of which an eighth are peculiar to the United States. The order contains two well marked groups: the Libellulidm, or dragon-flies proper, and the Agrionidm, demoiselles or damsel-flies, distinguished broadly by the fact that in the former the front wings are dis similar, and are held horizontally in repose; while in the latter the wings are alike and are held vertically when the insect rests. Another distinguishing feature is the fact that in the Libellulidm the eyes are sessile, sometimes meet ing on the top of the head, while in the Agrionidm the eyes are constricted at the base and peduncled. An important subdivision of the Libellulidm, regarded by some as a separate family, is the fEschnidm, which is characterized by the fact that the eyes touch on the top of the head. To this group belong many of the largest and most gaudy dragon-flies.
An excellent illustrated account of North American dragon-flies will be found in L. O. Howard's 'The Insect Book (1901), which con tains further references. For British species consult Lucas' (Handbook of British Dragon flies' (1899).