188 THYSANOPTERA AND ORTHOPTERA. 



HABITS OF THYSANOPTERA. 



Locomotion. 



Crawling seems to be the only method of locomotion common to all 

 thrips. Many are wingless, which precludes flight, and of both winged 

 and wingless species a considerable proportion apparently do not leap. 

 Crawling may be quite rapid, as, for example, in Thrips 'physo'pus, 

 which crawls 1 inch in about a second, or very slow, as in Aptinothrips 

 rufiis, which travels 1 inch in 10 or 12 seconds in the average specimen. 

 The tests were made on a sheet of smooth paper. In their natural 

 habitat crawling may be much slower. Thus, for example, Anthothrips 

 verbasci crawls more rapidly on paper than it does in the spikes of mul- 

 lein (Verhascum thapsus), which is covered with large branching hairs. 

 Temperature seems to have some effect on the general activity of thrips, 

 and so to alter the rate of crawling. For example, Chirothrips mani- 

 catus, though at all times slow, would allow me, on cool mornings in 

 August, to separate the florets of timothy between which it was located, 

 and to push it with my brush before it would move. Sex also appar- 

 ently has an influence on the rate of crawling. Thus, in Euthrips 

 tritici, the female is larger than the male and nearly always crawls more 

 rapidly, though the male is usually quicker in its individual movements, 

 as Jordan (1888, p. 610) points out for the Terebrantia in general. It 

 would doubtless be better here to say that rate of crawling is correlated 

 with size, rather than with sex. In Anthothrips verbasci, where there 

 is less difference in size between male and female, the male is rather the 

 more active crawler ; and occasionally even in Euthrips tritici the male 

 crawls more rapidly, the female in one instance crawling 1 inch in 3.5 

 sec, the male 1 inch in 2.0 sec. These unusual cases are probabty de- 

 termined by physiological state. 



Among the more rapid crawlers are Euthrips tritici, Ctenothrips brid- 

 welli, Thrips physopus, Thrips tahaci, and Aeolothrips fasciatus. Several 

 of the -Others, especially Aptinothrips rufus and the phloeophilous 

 species, are quite sluggish. Between these are all gradations of rapidity 

 of crawling. It is interesting to note that the active species, when dis- 

 turbed, nearly always come out of their concealed places if they are so 

 located, and either take to flight, or crawl away along exposed surfaces. 

 Of the more sluggish species, at least Anthothrips verbasci and the 

 phloeophilous ones crawl at once, when disturbed, into some other 

 neighboring crevice. 



Flight is the chief method of locomotion for several species, and is of 

 particular interest, as is shown later on, because of its relation to the 

 dissemination of these insects. Three species, Euthrips tritici, Thrips 

 physopus and Thrips tahaci, were found to be preeminently fliers; 



