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year by year in their annual reports, seldom giving- the cause of rarity 

 or abundance a thought. During the season which has just passed 

 the writer has given some attention to this subject, particularly in its 

 bearing upon insects affecting garden crops; and it is the object of this 

 paper to explain certain of the apparent phenomena of sudden appear- 

 ances and disappearances, the notes which follow being directed toward 

 showing that certain southern, mostly Austroriparian, forms of insects 

 occurring in and near the District of Columbia have been destroyed or 

 lessened in numbers by recent severely cold weather (as well as by other 

 causes), while certain northern, or Transition, species owe an evident 

 very perceptible increase to the same cause. 



As a preliminary it will be necessary to define briefly the location of 

 Washington as regards the life areas. 



THE LIFE ZONES ABOUT THE DISTRICT OF COLUMBIA. 



Inquiry of those who have collected for years in Maryland and Vir- 

 ginia, within a radius of 100 miles of Washington, brings out the fact that 

 many animals belonging to the Lower Austral, or more strictly Austro- 

 riparian, life zone maybe found within about 05 miles southward, while 

 a somewhat smaller number of Transition or Alleghaniau forms occur 

 within the same distance northward. 



At Piney Point, Md., zoologists, members of the Biological Survey 

 of this Department, and others, have found certain birds nesting which 

 are not known to breed farther north in this longitude. Mr. Schwarz, 

 who has done considerable collecting in this vicinity, particularly of 

 Coleoptera, informs me that many southern species occur tliere which 

 have never been taken farther north, and that many of these have found 

 their way up the Potomac into what is called the Eastern Branch, as 

 far north as Bladensburg, Md. (about 7 miles east and a little north of 

 Washington), that are identified with the Lower Austral life zone and 

 are seldom to be found much farther north. 



Xorthward the exact southern limit of the Transition life zone does 

 not appear to be so well defined. Some Subboreal and many Transition 

 forms of Coleoptera, Mr. .Schwarz has observed, are to be found on 

 some of the highest mountains near Harpers Ferry and between that 

 point and Penmar. in Pennsylvania, bordering the Maryland State line. 



During the writers first years in the city of Washington he was 

 impressed with the scarcity of individuals of many of the species 

 which were usually to be found in so much greater numbers farther 

 north, and was at first at a loss to account for the fact. Finally it was 

 surmised that the warmer weather of fall and winter interfered with 

 the proper hibernation of many species, the warm spells which are 

 usually experienced here during the winter inducing the hibernating 

 insects to come forth from their retreats and the subsequent sudden 

 cold snaps, for which this district is noted, being responsible for their 

 decrease, many of the insects being killed or so injured that they were 

 unable to survive the winter. 



