INSECT BEHAVIOR 353 
crawl downward; in other words, they are positively photo- 
tropic only so long as they are unfed. Here the kind of pho- 
totropism is dependent upon nutrition. 
Phototropism may be overruled by chemotropism and influ- 
enced by conditions of metabolism, as Parker found for the 
butterfly Vanessa antiopa. In his words: Vanessa antiopa, in 
bright sunlight, comes to rest with the head away from the 
source of light, that is, it is negatively phototropic, when the 
surface on which it settles is not perpendicular or very nearly 
perpendicular to the direction of the sun’s rays. When, how- 
ever, this surface is perpendicular to the sun’s rays the insect 
settles without reference to the direction of the rays. When 
feeding or near food [such as running sap] the butterflies do 
not respond phototropically. 
This negative phototropism is seen only in intense sunlight 
and after the butterfly has been on the wing, 1. e., after a cer- 
tain state of metabolism has been established. 
V. antiopa creeps and flies toward a source of light, that is, 
it is positively phototropic in its locomotor responses. Posi- 
tive phototropism also occurs in intense sunlight, and is not. 
dependent upon any particular phase of metabolism. 
Both negative and positive phototropism in this species are 
independent of the “ heat rays’ of sunlight. 
The position assumed in negative phototropism exposes the 
color patterns of the wings to fullest illumination, and prob- 
ably has to do with bringing the sexes together during the 
breeding season. 
To these may be added other important conclusions of 
Parker’s: 
No light reactions are obtained from the butterfly when 
shadows are thrown upon any part of the body except the 
head. When one eye is painted black the butterfly creeps or 
flies in circles with the unaffected eye always toward the cen- 
ter. When both eyes are painted black all phototropic re- 
sponses cease and the insect flies upward. Butterflies with 
normal eyes liberated in a perfectly dark room come to rest 
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