304 



THE STUDY OF INSECTS. 



If it is discovered before it has spread from these places it can 

 be confined by surrounding the field with a ditch, or it may be 



destroyed by spraying the 

 grass with Paris-green water. 

 Ordinarily, however, the 

 worms are not observed until 

 after the}' have begun to 

 march and are wide-spread. 

 In such cases it is customary 

 to protect fields of grain in 

 their path by surrounding 

 them with ditches with ver- 

 tical sides; it is well to dig 

 holes like post-holes at in- 

 tervals of a few rods in the bottom of such ditches. The 

 worms falling into the ditch are unable to get out, and crawl 

 along at the bottom and fall into these deeper holes. We 

 have seen these insects collected by the bushel in this way. 

 The Diver, Bellnra gortynidcs (Bel-lu'ra gor-tyn'i-des).- 

 One of the most remarkable exceptions to what are usually 

 the habits of members of this order is presented by the 

 larva of this species. This larva is able to descend into 

 water and remain there for a long time. It lives in the leaf- 

 stalks of the pond-lily. It bores a hole from the upper side 

 of the leaf into the petiole, which 

 it tunnels in some instances to the 

 depth of two feet or more below 

 the surface of the water. This 

 necessitates its remaining below 

 the surface of the water while 

 feeding. The writer has seen one 

 of these larvs remain under water FlG - *&-B*ii*r a go,-t y , t id es . 

 voluntarily for the space of a half-hour. The tracheae of these 

 larvae are unusually large, and we believe that they serve as 

 reservoirs of air for the use of the insect while under water. 

 The form of the hind end of the larva has also been modi- 



