NO. 1275. BEETLES OF THE DLSTRICT OF COLUMBIA— ULKE. ' 3 



The soil formed by the decomposition of the above .sediments and 

 roclcs is so varied in character that it is able to support no less than 

 1,400 species and varieties of vascular plants. 



Now, as about half of all the beetles depend upon plants for theii' 

 food, the greater the variety of food plants the larger we find tiie 

 nund)er of species of beetles. 



The geographical position and topographical features of the District 

 of Columbia also largely account for its diversified insect fauna. 



The coastal plain deposits, concealing the crystalline rocks of the 

 eastern and southern portions of the District, are formed into numer- 

 ous terraces, so that Washington is surrounded by low hills on all 

 sides, except where the Eastern Branch and southeastern shores of 

 the Potomac flatten out into marshy grounds. 



As the District lies on the border of the crystalline plateau and the 

 lower coastal formation and at the head of tide water on the great 

 lowland plain, which extends from New York to Richmond, the local 

 fauna has the composite character belonging to the upper austral, 

 lower austral, and the transition zones, or, to be more exact, it has 

 the facies of the Allegheny, Carolina, and austro-riparian regions, as 

 classified by Dr. C. Hart ]\lerriam.^ 



In a region so restricted and comparatively level, there are of course 

 no such changes in the temperature as in mountainous countries, 

 where we find forms of insects on the top of mountains ver}^ different 

 from those below, the former being always of a more northern type. 

 The appearance of northern and southern forms are here controlled by 

 the change of seasons, so in early spring we may always expect more 

 northern types, while in midsummer the southern ones predominate. 



There are other local causes which influence the character of our 

 fauna. The Potomac River ever}^ spring carries down quantities of 

 flood debris from the mountain districts, containing insects which 

 properly belong to higher elevations, for example, Phellopsis obcor- 

 data^ Pinodytes cryptopliagoldes^ Carehara longula^ Enchodes sericea, 

 and several Carabidfe, Longicorns, and Elateridte. Southern forms 

 have been observed chiefly in the middle and eastern part of the 

 District as along the Eastern Branch, where species were collected, 

 such as' Casnonia licdoviclana^ Cymmdls elegans^ Tludpiws dorsal !s^ and 

 several Chry some lidte . 



The great attraction of the electric lights for insects has also resulted 

 in the disco verj- of certain kinds, whose occurrence here was not pre- 

 viously known with certainty, such as Oinoj)hron lahiatimu Cllvina 

 punctigeifa^ Platynus picticoimis^ Rliantus calidus^ Ataenius figurator. 

 PleurojplioTus ventraUs, and Donne/ a hypoleuca^ which belong to the 

 austroriparian fauna. 



'The geographical T)istril>ntiun <if AniiiuiLs and I'lants iu Ndrth AimM-ica. Bull 

 Nat. Geog. Soc, 1895. 



