APOSEMATIC INSECTS CROWD TOGETHER 215 



procryptic to an aposematic type, the larvae still retaining 

 the characteristic shape and the attitude which follows 

 from the absence of the first three pairs of claspers, but 

 acquiring the habit, most unusual among Geometrid larvae, 

 of grouping themselves so that the effect of the warning 

 colours is accentuated — a habit not at all uncommon 

 among aposematic insects. 



The Peyitatomidae, highly odoriierous Hemiptera, resplend- 

 ent in green or blue and gold, commonly mass together. 

 In 1917 I met with a very marked instance of this 

 aggregation. An Acridian grasshopper, ^ conspicuously 

 coloured green, orange and black, and of typically apose- 

 matic habits, was proved very definitely to be distasteful 

 to a young monkey. When very young it is coal black, 

 speckled with yellow, and on several occasions large 

 numbers were found closely crowded together to form a 

 black mass at the end of a spray of herbage, which attracted 

 my attention, whereas a single individual from its small 

 size would easily have escaped notice. Some of these 

 black youngsters were given to a monkey, who would 

 not even taste them, although hungry, as was proved 

 by his subsequently eating other insects. Although the 

 habit of collecting in a mass, whereby the conspicuousness 

 'of an individual is much exaggerated, is most commonly 

 made use of for aposematic purposes, yet I have met 

 with an instance where a full effect of procrypsis was 

 only produced when a number of individuals collected 

 together in a certain way. The effect produced was a 

 likeness to a bird-dropping on a leaf, and could not so 

 well have been produced by a single individual. 



The species concerned is the Bombycid moth, Trilocha 

 obliquissima, of which the type specimen, from Angola, 

 was the only one in the British Museum collection. A 

 company of very young caterpillars was found on Bugalla 

 Island on a leaf of a Sapotaceous tree, Chrysophyllum. 



^ Zonocerus elegans. 



