346 THE GYPSY MOTH. 



mining, as fully as possible, how far the males might be 

 assembled by the females. The question to be solved was, 

 from how great a distance can a male moth recognize and 

 follow up the scent of the female ? There are many condi- 

 tions affecting the distance over which assembling may be 

 possible. The following are a few of the more important : 



1. The place in which the female emerges. If this occurs 

 in a stone wall or rubbish heap, or in a hollow tree, the odor 

 could not possibly escape and be diffused as fully as if the 

 moth were exposed to the air on the outside of the tree, and 

 at some height from the ground. 



2. The condition of either the male or female after emerg- 

 ing. If the female is strong and in perfect condition, she 

 will assemble more males than a female partly denuded. If 

 the male is strong and active, he will, of course, be superior 

 in flight and action to one partially crippled or enfeebled. 



3. The direction and velocity of the wind. The wind 

 must blow from the place where the female emerges toward 

 some place where male moths occur. A wind of high velocity 

 will carry the odors farther than a light breeze, but, at the 

 same time, offer greater resistance to the flight of the male 

 while following up the scent. 



4. Weather and temperature. The flight of the males 

 is more vigorous on bright, warm days than when the air is 

 cold and damp. 



5. The contour of the land and whether it is wooded or 

 not, thus forming wind-breaks. If there are forests or hills 

 between the female in question and the males to be attracted, 

 they will interfere with the direct passage of currents of air 

 carrying the odor, so that males may fail to be attracted 

 from much shorter distances than if in a region without these 

 obstructions. 



Details of the Experiments. 



A level area on the salt marsh between Edgeworth and 

 Somerville, entirely free from obstructions, was selected for 

 the scene of operations, and stations were established from 

 day to day, according to the direction of the wind. 



Stations. The first station chosen in each experiment 

 was the one where one or more females were to be located, 



