538 



THE COMMUNITY 



to pack suitable niches. The ladybird 

 beetles are notable in this regard." Such 

 aggregations may consist ot many different 

 species of ladybird beetles, other beetles, 

 bugs, spiders, earthworms, and other organ- 

 isms, or they may consist of one species. 

 Such heterotypic and homotypic aggrega- 

 tions may hold as many as 10,000 macro- 

 scopic individuals per square meter of forest 

 tioor. 



Forest leaf mold and forest margins are 

 notable, but not unique, sites for hiber- 

 nacula. In western United States the rapa- 

 cious tiger beetles, Cicindela oregona, 

 abandon their solitary, predaceous Ute at 

 the approach of winter, and burrow under 

 flat rocks to form a gregarious overwinter- 

 ing aggregation (Blaisdell, 1912), and hun- 

 dreds of histerid beetles, of several species 

 of Saprinus, form extensive gatherings in 

 bare sandy patches at the approach of 

 winter in western Ukraine (Spett, 1925). 

 In the Chicago area queens of the white- 

 faced hornet (Vespula maculata) over- 

 winter in log mold. Certain mound-building 

 ants {Formica ulkei and F. exsectoides) 

 form hibernating masses of individuals in 

 the deep nest galleries above the water 

 table, between November 1 and April 11 

 (Hohnquist, 1926, 1928, 1928a; Dreyer, 

 1932, 1938). 



Many terrestrial snails adjust by sealing 

 the aperture with a thin epiphragm of 

 secreted mucus. Many crayfish burrow into 

 the subaqueous floor of ponds (Creaser, 

 1931), and there is a long list of organisms 

 that overwinter in frozen aquatic com- 

 munities by encystment (various protozoans, 

 rotifers, nematodes, annelids and entomos- 

 tracans). 



Encystment would appear to be a general 

 adjustment to adverse conditions, of which 

 those obtaining in winter are simply one 

 of a number of groups of stimuH. This 

 seems clear from the evidence of investi- 

 gators who find that encystment in proto- 

 zoans and entomostracans can be brought 

 about by low or high temperatures, lack of 

 food, presence of an unfavorable concentra- 

 tion of waste products, or lack of oxygen 



' For overwintering aggregations in general, 

 see p. 393; for aggregations of coccinellid 

 beetles, see Hamilton, 1885; Schwarz, 1891; 

 Cook, 1898; Calvert, 1899; Carnes, 1912; Van 

 Dyke, 1919; Hawkes, 1920; Park, 1930; Allee, 

 1931. 



(Mast, 1912, 1917; Birge and Juday, 

 1911). 



In many of these cases of adjustment, 

 whether by encystment or moving into pro- 

 tected floors, loss of organismal water ap- 

 pears to parallel, if not precede, the loss 

 of physiologically accessible water in the 



PERIODICITY IN COLD HARDINESS 



SEPT. OCT 



MAY IJUNE 



Fig. 185. Degree of cold hardiness is cor- 

 related with ( 1 ) seasonal periodicity of tem- 

 perature, and (2) normal seasonal fluctuation 

 in temperature in the community or habitat 

 in which a given species is resident. (After 

 Payne. ) 



community approaching winter. Encyst- 

 ment in protozoans, among others, involves 

 desiccation. Again, many insects that move 

 into forest floor hibernacula have previously 

 undergone some dehydration (Payne, 1926, 

 1927, 1927a, 1928, 1929). 



Payne's work on the development of cold 

 hardiness in insects is of interest here, since 

 her experimental data have broad com- 

 munity impUcations. It was demonstrated 

 (Fig. 185) (1) that degree of cold hardi- 



