2 DRAGOXFLIES OF OHIO. 



is accessible to most students in the papers cited and in 

 the Synoptic Catalogue of W. F. Kirb\'. References 

 will be made, b}' foot notes, to descriptions made since 

 the papers cited were published. 



Dragonflies occur in most parts of the earth. Rep- 

 'resentatives of this ancient race fl\' beyond the Arctic 

 Circle and at an elevation of 10,000 feet. However, 

 they are heat-loving insects and of course are more 

 numerous in tropical and sub-tropical countries than 

 elsewhere. The number of known species in the whole 

 world exceeds 2000; in North America about 300; and 

 in Ohio 100. 



The Odonate fauna of Ohio is essentialh' rich in 

 species ancj in the number of individuals. The great 

 lake system on the north, and the Ohio River on the 

 south afford favorable conditions for their life, and 

 avenues for their approach from south-west and north- 

 west; while our diversified area Avith its numerous 

 rivers and morasses is not an unfavorable habitat. 

 The number of living species listed for Great Britain is 

 forty-five, for France seventy, and for all Europe one 

 hundred and twenty. Still our Century of Odonates, 

 it is supposed, represents a waning race; once, when the 

 climate w^as more nearh' tropical, the number was 

 probably much greater. A question of equal interest is 

 whether the results of the changes incident to civiliza- 

 tion have produced a diminution of our resident species. 

 There is an impression abroad that we have lost species 

 in, for example, the present century; that some species 

 cannot withstand the consequences of stream pollution, 

 drainage of morasses, and the more inconstant charac- 

 ter of the stre'ams and ponds. There are no data for 

 determining the question. It is the opinion of the 

 writer that some few forms once residents are no longer 

 within our limits, but that others have taken up their 

 homes here at the same time ; in fact it appears proba- 

 ble that the number has increased rather than dimin- 

 ished up to the present time. 



