184 THYSANOPTERA AND ORTHOPTERA. 



Thrips physopus 



Thrips tahaci 

 b. Phloeophilous division, inhabiting bark. 



Allothrips 7negacephalus 



Neothrips corticis 



Trichothrips beachi (?) 



Trichothrips tridentatus 

 2. Superficial, living in exposed situations, 

 a. Poephilous division, li\dng on grasses. 



Anaphothrips striatus 



Aptinotkrips rufus (with its variety connaticornii) 



Baliothrips basalis 

 h. Phyllophilous division, found on leaves other than grasses. 



Ctenothrips hridivelli 



Heterothrips salicis 



Phyllothrips aspersus 



Trichothrips hrevicruralis 



It is not meant by this classification that a given species is to be 

 found only in the situations designated. Even Euthrips tritici, which 

 is almost exclusively anthophilous, was taken on leaves of blackberry 

 (Ruhus canadensis), and in several other equally superficial situations. 

 Some species really belong to more than one group. For example, 

 Chirothrips manicatus is to be found on grass and in flowers. Such as 

 these have been placed in the group which the majority of collections 

 would indicate as the principal one. Other species have been found 

 in too small numbers to warrant as yet a final ecological grouping. 

 These are placed tentatively in the groups indicated by the few col- 

 lections made. Further work is needed on the less common species; 

 but care should be taken to note the condition of the indi\aduals when 

 captured. Thus, while some species undoubtedly live all the year 

 round under bark scales, others apparently only hibernate there. Such 

 species belong to the group indicated hj their habitat during their sea- 

 son of activity. 



Factors determining Habitat. 



The C[uestion naturally arises, what are the factors which determine 

 the habitat of a given species?- Why is one species nearly always in 

 flowers, another exclusively on bark? In the great majority of cases, 

 the home of any animal is where proper food may be found or its ene- 

 mies avoided or both. Other factors, such as climatic conditions, often 

 play a role, but in a cosmopolitan order like the Thysanoptera this role 

 can not, I believe, be other than a minor one. To the question regard- 



