INSECT BEHAVIOR 349 
parallel with the long axis of the trunk of the tree and the 
head pointing upwards. When disturbed they fly off, but 
very soon alight nearer the earth and again walk upward.’ 
(Wheeler.) Coccinellidze and cockroaches are also negatively 
geotropic. The latter insects, as Loeb has observed, tend to 
leave a horizontal surface but come to rest on a surface that 
is vertical or as nearly so as possible. 
Wheeler says, “ Geotropic as well as anemotropic orienta- 
tion 1s not altered for the sake of response to hight. Even if 
the insect be strongly heliotropic, as 1s the case in most Dip- 
tera, it orients itself to the wind or to gravity no matter 
‘whence the light may fall.” 
Phototropism.—It is a matter of common observation that 
house flies, butterflies, bees and many other diurnal insects fly 
toward the hght; and that cockroaches and bedbugs avoid the 
light. These are familiar examples of phototropism, or the 
“control of the direction of locomotion by light.” The pho- 
Fic. 280. 
A, tracks made on paper by a larva of Lucilia cesar moving out of a spot of ink 
under the influence of light; A and Bs show respectively the first and second 
directions of the light. B, tracks made in the dark.—After PoucHeEr. 
