166 



THE AMERICAN NATURALIST [Vol. XLVIII 



pupated, and many were crawling on the inside of the 

 bag. The spike that was exposed, on the other hand, bore 

 but little over half the number of larvae that were on the 

 protected one, none were quite full grown, and none had 

 pupated. Since nothing in the climatic conditions (heavy 

 rains, for example) could have caused this difference, 

 it is to be inferred that predatory bugs had devoured the 

 larger larvae in considerable numbers. 



Yet Anthothrips verbasci, according to my earlier ex- 

 planation, ' 'chooses" its habitat almost exclusively in re- 

 lation to food, protection being a minor consideration. 



Can we not explain habitat and behavior in these in- 

 sects in some way not implying choice, especially choice 

 between conflicting preferences ! May we not assume that 

 certain elements of behavior are what they are without 

 reference to their usefulness? If we grant the possibility 

 of an affirmative answer to these questions, the experi- 

 ments about to be described will have significance. 



Experiments on Behavioe 

 The following experiments were designed to show the 

 reaction of the commoner species of Thysanoptera to 

 what seemed to me the most probable external agents 

 affecting their distribution and behavior, namely, light, 

 contact and gravity. Inasmuch as I was not primarily 

 interested in hoiv a given reaction was brought about, but 

 only in its end result, the experiments were rather crude. 

 Eefinements were unnecessary, and their omission en- 

 abled me to use much greater numbers of individuals than 

 would otherwise have been possible. From ten to forty 

 repetitions of each test were usually made. The experi- 

 ments are described by species, only representative ex- 

 periments being given. 



Euthrips tritici 

 Light. Exp. 1.— Adults of this species were placed in 

 a glass tube about three feet long and one inch in diam- 

 eter, closed at the ends with corks. One end of the tube 



