HABITS OF THE LARVA OF BELLURA MELANOPYGA. Ill 



motion, even with full-grown larvae, and little or no headway 

 can be made against them. Owing to the fact that the situations 

 which are favorable for the growth of their food plant are char- 

 acterized by quiet water, the interference with dissemination due 

 to surface disturbances is not great. 



The advantage to the larva of this surface swimming is obvious. 

 It must have free air and many of the journeys which it makes 

 require a longer time than it can remain under water but the 

 ability to swim on the surface makes it possible to secure air 

 with ease. 



When larvae are placed beneath the surface of the water and 

 released they immediately orient themselves in such a way that 

 the head is towards the surface and, by means of the undulatory 

 movements of the body, swim diagonally upward, continuing 

 the effort until the surface is reached. Swimming below the 

 surface is much less efficient than on the surface but it is usually 

 effectual in assisting the larva in getting back to the top. When 

 submerged they appear to lack the ability to do effective climbing 

 on stems and other objects with which they come in contact. 



When swimming on the surface the larva shows a strong ten- 

 dency to climb upon any object which comes in its way and in 

 case the object is immovable, has a smooth upper surface, is 

 above the surface of the water, and broad enough to support the 

 greater part of the length of the body, it will usually come to 

 rest for a time. In cases w T here the object is very limited in 

 size, as for example a stick, twig, or stem, the larva usually climbs 

 over it and continues the journey. Larvae may desert the leaves 

 and voluntarily take to the water. When once in the water the 

 swimming movements are usually kept up continuously until 

 another flat, emergent object is reached. When a larva deserts 

 one lily leaf the search for another food plant is entirely a random 

 one and the contact with another leaf seems to be purely acci- 

 dental. It merely keeps on swimming until it happens to choose 

 a course which leads to a leaf. The larva apparently has no 

 means of recognizing the presence of a food plant except when 

 in contact with it. The writer observed instances where larvae 

 swam aimlessly about for a half hour without finding a food plant, 

 having passed several times within a centimeter of a lily leaf. 



