October, '17] DUNN: cocoanut-tree caterpillar 479 



Before reaching maturity they always gather in large numbers and 

 build nests for themselves. This nest building habit of these cater- 

 pillars appears to be peculiar to themselves as there seems to be no 

 record of any other lepidopterous insects utilizing leaves to form a 

 nest to the same extent as the B. isthmia does. 



The nests are formed by bringing the ends of the leaflets on opposite 

 sides of the main stalk of a leaf together so that they extend downward, 

 and at the lower end the narrowness of the leaflets give to the whole 

 affair the appearance of a long funnel shaped bag. The leaflets are 

 fastened together with a silken web spun by the caterpillars and they 

 also line the entire nest with an inner lining of this silk. Many of the 

 large nests are divided into several compartments by having parti- 

 tions of this silken floss extending longitudinally in the nests. This 

 inner lining of silken web does not reach to the ends of the leaflets form- 

 ing the nest, thus leaving openings at the bottom for all the excrement 

 within the nest to drop to the ground. 



As the leaflets of a cocoanut tree extend at nearly an obtuse angle 

 it evidently requires considerable skill to bring the ends down and 

 together in order to fasten them in the positions they occupy in the 

 nests, and this is probably accomplished by the weight of large num- 

 bers of the caterpillars. 



Close observation of this nest building has so far been impossible. 

 The low trees which would permit of such observation have been 

 remarkably free from infestation, and for the higher trees neither the 

 time nor the necessary conveniences have been available. 



One nest recently examined was 4 feet and 4 inches in length and 

 14 inches in width at the top, measuring over all the leaflets fastened 

 together. Thirty-three leaflets were fastened together to form this 

 nest, 16 on one side and 17 on the other. 



The number of caterpillars found in a nest varies greatly, ranging 

 from as low as 50 up to as high as 2,000. Apparently a great deal 

 depends upon the size of the nest and the time that it is cut down. 

 Undoubtedly, in a small nest, many of the caterpillars, finding their 

 quarters overcrowded, emigrate to large nests in close proximity, or 

 there may have been only a small number to start with when the nest 

 was begun. Nests that are cut down late in the season are liable to 

 contain smaller colonies than those found earlier, as they are then 

 full grown and many may have already left the nest to find suitable 

 places for pupation. 



In the particular nest just mentioned, 615 caterpillars were found. 

 All were full grown and ready to pupate and there were probably many 

 more that had left the nest to pupate before it had been cut down. 



Usually there are but one or two nests to be found in a tree, but 



