158 • [J^iy- 



ON Tllli MOVEMENTS OF THE "JUMPING BEAN." 

 BY DAVID ROLLO, University College, Dundee. 



In the bean of Croton collujuaja there is often found the larva 

 of Carpocapsa salt/fans, which by its movement inside produces the 

 peculiar jerking action from which the name " Jumping Beau " is 

 derived. The pale yellow larva is about 10 mm. long and 2 br'oad, 

 while the beau is about 9 mm. long by 7 mm. high. The contents of 

 the bean have been completely hollowed out, leaving a shell of about 

 5 mm. thick. The shell weighs '05 gr. and the larva about '025 gr. 

 In addition to the normal six thoracic legs, eight abdominal legs and 

 two claspers, the caterpillar has on the head a brown plate (clypeus) 

 which acts as a protective shield when the larva strikes the bean 

 a blow. By removing one side of a bean and replacing this with 

 a piece of micro-cover-glass, the movements of the animal were 

 observed. On gently warming the bean the larva is seen to creep 

 about in an excited manner. Sometimes it swings its head from one 



A A^ B b' 



side to the other, then by raising its body iuto position A, it delivers 

 repeated blows on the shell. In most positions this would only 

 produce a slight oscillation of the bean ; but when the larva causes 

 the bean to jump, it is not at the bottom but fixed to the upper side 

 of the bean, in position B. When its head comes in contact with the 

 shell, the larva is still curved, and the reaction seems to straighten it 

 when it again rears up to deliver more blows. A tap may be heard 

 when it strikes a blow, and the brown plate or clypeus appears 

 to be hard. 



I have never seen the larva fixed to the part of the bean next 

 the support and trying to strike the top ; nor has it ever jumped 

 more than 3 mm. high and 6 mm. along. The larva appears to desire 

 to remain inside the bean : on removing the glass it was covered with 

 a web and all corners had been closed up. 



I have had one for twenty-eight days in a small glass bulb, and 

 although no food has been supplied, it still moves about and tries to 

 cause a jump. 



April, 1905. 



