FIELD WORK ON HYMENOPTERA. 145 



as gallflies. The green galls, if closed, are most probably 

 made by gallflies; besides this, when you cut them open, 

 if the gall is due to a gallfly, there will be found inside 

 nothing save the immature larval or pupal hymenopter- 

 ous gallfly; while in galls made by some of the other 

 gall-forming agents, it is the mother that enters the gall 

 and rears her young within its increasing structure, and 

 there will be found the opening by which the escape of the 

 insect has been made. 



Suggestions for the study of the ichneumons may be 

 found in the discussion of the big Thalessa and the 

 Pigeon Horntail. If a caterpillar outwardly in good 

 condition be found dead on a leaf, pick off the leaf with 

 the caterpillar on it, and store it in some box with a good 

 lid; put a label on the lid and also on the box so that it 

 may not be lost. Look often at the caterpillar for 

 developments. If the parasitic insects have not already 

 escaped you will be able to trace the life history of the 

 parasites from the larvae, which will appear, possibly, 

 beyond the body wall of the caterpillar when they have 

 attained their larval maturity and go through the pupal 

 transformation. And some day you may find some tiny 

 winged creatures flying about in the box when you open 

 it. When these do appear they should be given their 

 liberty out of doors to repeat the beneficial work of their 

 kind. Whenever you have learned to know a harmful 

 insect, miss no opportunity to kill it; in so doing you 

 destroy not only that insect, but also all of its descendants. 

 When you learn to know a beneficial insect, and this 

 may mean one or more of the enemies of the first sort, 

 be sure that neither you nor anyone else harms it; you 

 will thus be able to avail yourself of the good done by it 

 and by all of its descendants left unharmed. 



