158 



is the maker of the gall — four inquilinous Cecidomyia — an inquilinous 

 saw-fly (Hymenoptera) — five distinct species of Microlepidoptera, 

 some feeding on the external leaves of the gall, and some burrowing 

 into the heart of the cabbage, but scarcely ever penetrating into the 

 central cell, so as to destroy the larva that provides them with food 

 and lodging — two or three Coleoptera — a Psocus (Pseiidoneiiroptera) 

 — a Heteropterous insect found in several other willow-galls — an 

 Aphis which is also found on the leaves of the willow, but pecu- 

 liarly affects this gall — and preying on the Aphides the larva of 

 a Chrysopa (Neuroptera) and the larva of a Syrphide (Diptera) — 

 besides four or five species of Chalcididae, one Braconide Ichneumon 

 (Hymenoptera) and one Tachinide (Diptera), which prey on the 

 Cecidomyia and the Microlepidoptera — making altogether about two 

 dozen distinct species and representing every one of the eight Or- 

 ders. ... If this one little gall and the insect that produces it 

 were swept out of existence, how the whole world of insects would 

 be convulsed as by an earthquake ! How many species would be com- 

 pelled to resort for food to other sources, thereby grievously disar- 

 ranging the due balance of Insect Life! How many others would 

 probably perish from off the face of the earth, or be greatly reduced 

 in numbers ! Yet to the eye of the common observer this gall is noth- 

 ing but an unmeaning mass of leaves, of the origin and history of 

 which he knows nothing and cares nothing!" 



With this conception of a community in mind it is only necessary 

 to refer to the following diagram (Fig. i8) to see how immaterial 

 it is as to where one begins to take up this thread of interrelations, 

 for sooner or later every animal and plant in the association will have 

 to be passed in review and its influence recognized as a response to 

 its conditions of life. 



ECOLOGICALLY ANNOTATED LIST 



I. Prairie Invertebrates 



An exhaustive study of the animal ecology of a region or an as- 

 sociation must be based upon a thorough investigation of the ecolog- 

 ical relations of the individual animals composing it. An ideal an- 

 notated list in an ecological paper should, therefore, include for each 

 species a complete account of its life history, its behavior, its physi- 

 ology, and the structural features which would in any way contribute 

 to an understanding of the response of the animal to its organic and 

 inorganic environment. At present we have no such knowledge of 

 the animals of any locality or of any complex association of animals. 



