1968 ] 
Robinson — Behavior of Pterinoxylus 
205 
gigas during a wing erection display. Rehn (1957) gave an incom- 
plete description of the female display in Pterinoxylus spinulosus 
quoting from the observations of Scholander and Ruud made at Barro 
Colorado Island. Only in the case of E. goliath were both sexes 
observed. In this species both sexes have large wings and their 
display was essentially similar (Bedford and Chinnick, loc. cit.)* 
Orxines macklotti and Metriotes diocles have displays which in both 
sexes involve vertical wing erection without sound production. The 
tendency to display in O. macklotti is much stronger in females than 
males whereas the tendency to jump from the substrate in response 
to tactile stimulation is greater in males. A stridulatory organ on 
the third antennal joint has been described for the leaf insect 
Pulchriphy Ilium crurifolium (Serville), where it is restricted to the 
female sex (Henry 1924). My own experience with Phyllium 
bioculatum Gray shows that the female does not use the stridulatory 
apparatus when disturbed or restrained or in any other context 
which would suggest that its function was defensive. Thus the 
display of P. spinulosus seems to be unique as far as phasmids are 
concerned in that although both sexes display the displays differ 
markedly in form. 
Sound production by insects which are attacked, disturbed or re- 
strained by other animals is well known for insects of several orders 
(see, for instance, Alexander i960 and Dumortier 1963). There 
has been considerable discussion about the function of these sounds. 
In some animals they serve to alert conspecifics but there is no direct 
proof of a startle function. 
A further point of interest with regard to phasmid startle displays 
is that these, unlike other defensive adaptations in phasmids (with 
the exception of escape flight) are available only to the adult. So 
far I have not found any defensive adaptations which are present 
in the immature stages which are additional to those of the adult 
and might compensate for the lack of the full adult defensive reper- 
toire. A possible exception to this may be the fact that color changes 
occur during the first instar of some species (e.g. Phyllium sp.) and 
at the final ecdysis in others (e.g, Metriotes diocles Westw.) The 
first of these can be related to the fact that many phasmids hatch on 
the forest floor where the predominant color may differ markedly 
from the predominant color of the twigs on their food plant. The 
second type may be related to a change in the ecology of the animal 
at maturity. Such a change could render the animal more vulnerable 
to predation and might explain why the nymphs can survive with 
