THE INSECT ASSOCIATION OF A LOCAL ENVIRONMENTAL .COMPLEX. 
49 
be stated here : “ (l) The animals studied react to air of a given high rate of 
evaporation whether the evaporation is due to moisture, temperature, or rate of 
movement ; (2) the sign and degree of reaction to the given rate of evaporation 
are in accord with the comparative rates of evaporation in the habitats from which 
the animals were collected ; (3) the animals of a given habitat are in general agree- 
ment in the matter of sign and degree of reaction ; the minor differences which 
occur are related to vertical conditions and kind of integument, but no agreement 
between survival time and habitat when a number of members of a community are 
taken together.” 
The Insect Association. 
A large number of the insect species which occur in meadows and pastures are 
not peculiar to them. The real index of an insect’s habitat is where it breeds, and, 
although this may be the same as where it feeds during various of its life-history 
stages, there are innumerable instances where this is not so. If this fundamental 
principle be recognised, it is a very simple matter to distinguish between those 
forms which are proper or peculiar to an association ( endemic ) and those which are 
invaders {jpolydemic ) , provided always the larval habits are known. The second of 
these classes may be again subdivided into two groups, viz. : — 1. Temporary in- 
vaders. 2. Permanent invaders. Only the first of these concern us. The second 
may be better considered in a discussion of the phenomena of succession. In any 
given area the physical conditions, climatic or topographical, may undergo such a 
change that its fauna or certain members of it can no longer exist within the en- 
vironment. The new conditions may, however, be suitable to another set of 
organisms which invade the locality and make it their own. Thus a new order of 
things is established, lasting only so long as the fresh conditions do not vary to any 
great extent. Similar results may also be produced by a change of the biological 
conditions. In time, living organisms may render their surroundings toxic to their 
own kind by the accumulation of waste matter or excreta, or it may be that the 
food supply will give out. On the other hand, other organisms will thrive in just 
those conditions and replace their benefactors (Shelford, pp. 308, 309).* In the 
process of reduction and demolition of a felled log to humus one obtains a good idea 
of what is meant by succession, where the Scolytid and large Cerambycid beetles are 
followed by the larvae of Elateridae. With the advance of decay these forms give 
place to the larvae of Muscidae, Tipulidae, Mycetophilidae and attendant predaceous 
forms, such as the larvae of Leptidae, Xylophagidae, Staphylinidae, and Carabidae. 
Ants will frequently rear their broods in the old burrows of the wood-boring forms. 
In the final stages, when fungus and moisture have aided materially in reducing the 
wood to pulp, earthworms enter and complete the processes of demolition. 
We also recognise definite changes or succession of organisms from season to 
* Op. cit. 
