206 PHILIP p. CALVKKT. 



iuger (Ent. Nach. vii, p. 187j. The Egyptian Bee-eater (Merops persicus) includes 

 dragonflies in its diet (Allen, Ibis, 1862, p. 360). 



Means of Distrihidion. — The highly-developed power of flight pos- 

 sessed by the Odonata constitutes a most efficient means of distribu- 

 tion, to which must be added the important aid afforded by the winds. 

 Migratory swarms composed of many individuals of one or more 

 species have frequently been observed. Koppen has brought together 

 the records of sixteen migrations from 1494 to 1868 (Stett. Ent. Zeit. 

 1871, pp. 183-90), and Beutenmiiller (54, pp. 161-2) adds twenty- 

 six instances, mostly between 1872 and 1888. Representatives of 

 the Calopteryginse, Agrioninse, Aeschninse and Libellulinie have 

 taken part in such migrations, but the chief migratory species is 

 Libellula quadrimaculata, swarms of which have been met with both 

 in Europe and in North America. Annual migrations of this spe- 

 cies occur in the Charente Inferieure according to Riveau, and a 

 similar statement is made by Brown for Aeschna eremita (= clepsydra 

 Say, see post) in Wisconsin. The cause of these migrations is un- 

 known ; in some cases they are believed to be due to the drying up 

 of ponds, but this explanation does not appear to account for all the 

 known instances. 



Dragonflies have frequently been met with flying over the ocean, 

 many miles from land, so that bodies of water of moderate size do 

 not offer barriers to their dispersal. The observations of Schwarz 

 (Proc. Ent. Soc Wash, i, p. 208-15) lead to the conclusion, however, 

 that many individuals do fall into the water and so perish. 



The number of eggs laid by a single female is very variable, but 

 often amounts to several hundreds, and each imago pairs more than 

 once. As a considerable number of eggs are usually laid in each 

 body of water, a number of imagos is to be expected at that locality, 

 for at least a short period after imagination. Eggs and nymphs, 

 however, are probably frequently transported from one place to 

 another by currents of water. 



GEOGRAPHICAL DISTRIBUTION. 



The Odonata are found over nearly all parts of the world, being, 

 of course, more numerous in the tropics. Nowheres are they known 

 to pass beyond the northern and southern limits of permanent human 

 habitation, as these are shown by Bartholomew (Hand Atlas), but 

 they probably occur above the northern limit of trees. The most 

 northern localities known for these insects are near Alten, in Fin- 



