30 UNITED STATES NATIONAL MUSEUM BULLETIN 2 76 



but, on the other hand, caterpillars may escape by hiding in the tent. 

 Wellington (1957) noted that tachinid flies were more attracted to 

 clusters of larvae than to individuals, but pointed out that this may 

 be an advantage to the population as a whole, since the less active, 

 sluggish individuals which are less likely to become adults spend more 

 time in clusters than the active larvae, and thus would tend to absorb 

 a higher percentage of the parasite eggs. 



Larvae often are found with several eggs attached on or near the 

 head (figs. 339, 370). On several occasions during this study larvae 

 which were being molested by tachinids have been observed to jerk 

 violently the anterior part of their body from side to side, efTectively 

 preventing the deposition of eggs on them.selves, and forcing the 

 tachinids to approach less active larvae. (If the eggs are not laid 

 near the head, the caterpillar can easily chew them off.) If the dis- 

 turbance by tachinids or other means is severe enough, older larvae 

 have been observed to drop to the ground, and in the case of younger 

 larvae they may spin down on silk threads and hang suspended for a 

 while before making their way back to the tent. 



It is not known whether the larvae which show the jerking reaction 

 are the "active" or "sluggish" types described by Wellington, but it 

 is difficult to imagine how a tachinid could lay several eggs on an 

 individual which reacted this way, and any larva with several eggs on 

 it must certainly not have been very active. This same jerking move- 

 ment has been observed when branches bearing larvae have been 

 suddenly jarred, and Stretch (1881) and Ancona (1930) noticed a 

 similar reaction when loud noises were made near tents. A loud shout is 

 sufficient to set off the jerking response. Therefore, the jerking response 

 appears to be a general type of response that is initiated in some 

 individuals and/or colonies by unusual disturbances of various sorts. 



It remains to be determined whether the tent provides more protec- 

 tion than attraction to potential enemies, but a tent certainly would 

 not hamper a large predator such as a bird once it comes to realize 

 there is a meal inside, and smaller enemies such as ants and spiders 

 can wait for larvae to come out to feed, or even crawl inside the tent 

 searching for them, although this may not always be done with safety 

 from the predator's viewpoint. Sullivan and Green (1950) reported 

 seeing pentatomid predators being entangled in silk spun by large 

 larvae of M. americanum, and that this behavior did not appear to be 

 entirely accidental in some instances. 



As far as disease is concerned, a group of caterpillars which returns 

 to the same tent time after time would seem likely to pick up any 

 disease organisms that are present in the tent, since it contains much 

 frass, and diseased caterpillars often die inside. Wellington (1960) 



