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 they 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, Bellura gortynides (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 larvae remain under water F,G * 368.— Beiium gortynides. 
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- 
Fig. 367 .—Leucania unipuncta. 
