14 UNITED STATES NATIONAL MUSEUM BULLETIN 2 76 



food as all of the earlier instars combined. By the time the last instar 

 has been reached, caterpillars are about 2 inches long, have lost their 

 gregarious habit, and ti'avel extensively searching for food. They are 

 rather indiscriminate about what they eat at this stage, and this has 

 resulted in many species of plants being listed as hosts even though egg 

 masses may never be laid on them. 



Toward the end of the last instar they become quite restless and 

 often are seen wandering about in an apparently aimless way. Even- 

 tually they select an appropriate site in which to spin their cocoons, 

 such as within the old tent, inside logs, beneath loose bark, between 

 folded leaves, etc. The cocoons are about 1 inch long, fairly loosely 

 constructed, and colored white or yellow by a powdery material 

 dispersed between the strands of silk. The prepupal stage takes about 

 2 days and the pupal stage up to 2 weeks, depending on temperatures. 



The adults emerge in late afternoon or early evening. Mating may 

 take place the first day, and the female soon lays her eggs on a suit- 

 able host. Both males and females die in a few days since functional 

 mouthparts are absent and no food can be taken. 



Methods 



The major part of the field work was carried out during the springs 

 and summers of 1960 and 1961, with some additional work done in 

 the spring of 1962. The general plan was to collect larvae and rear 

 them to adults, starting in the south at low elevations and working 

 north as the season progressed. 



It is apparent that an area as large as western North America can- 

 not be studied both intensively and extensively in two field seasons, 

 and that only relatively widely scattered samples can be taken except 

 in areas believed to be of particular importance for one reason or 

 another. Possibly the most important reason for covering a large area 

 is to determine what forms are present in areas that have never been 

 collected and to determine the distributional limits of known popula- 

 tions. All available infomiation pointed to much greater variations 

 from area to area rather than from valley to alpine areas. Therefore, 

 priority was given to covering as much area as possible. Consequently, 

 in many areas it was not possible to study the alpine populations before 

 it was necessary to move north to study more northern populations 

 occurring at lower elevations. 



All of the field collecting was based on the fact that those "species" 

 of tent caterpillars whose status was doubtful and most in need of 

 study build a rather conspicuous tent which can be spotted with little 



