green moth, Bryophila muralis {glandifera) (PI. II, fig. i). This 

 is a medium-size moth, about i to i\ in. across the spread wings, 

 which is found during the summer resting on walls and rocks around 

 our south and west coasts. Its coloration is very similar to that 

 of old lichen-covered stucco, but is exceedingly variable within 

 definite limits, and careful study soon provides a theory to account 

 for this. The caterpillars feed upon the green confervoid growths 

 to be found on all old stone- and brick-work, especially after damp 

 weather, and consequently each wall has a colony of them to itself, 

 large or small. 



Now, of course, the general tone of colour on an old stone wall is 

 different from that of old brick, and in different localities there is 

 even greater variation due to local conditions and the type of the 

 local rocks. But it will be found that the majority of the moths on 

 each wall harmonise so perfectly with it as to be very difficult to 

 find ; and the conclusion at once presents itself, that those which do 

 not do so in each succeeding generation have met with a speedy 

 and violent death from natural causes, leaving those that are best 

 protected to propagate their species, and producing more or less on 

 each wall, certainly in each locality, a varietal race, and, of course, 

 in the aggregate accounting very satisfactorily for the great variability 

 of the insect. 



Another very potent factor bearing on the position selected by an 

 insect for resting is the weather. They object to wind, and most 

 moths object to sunshine as well. 



My own experience has led me to conclude that it is very little 

 use searching on palings or the sides of tree-trunks which have faced 

 the wind during the previous night, especially if it has been at all 

 strong, and I have often been struck with the particular potency of 

 this factor when cycling or walking along a road bordered on both 

 sides with palings, at finding practically all the moths on one side 

 of the road. I feel so confident on this point now that I pay very 

 little attention to the side which has been facing the wind of the 

 previous night. The point that I want to settle to my own satisfac- 

 tion is — what happens when the sun shines full on the sheltered side 

 of a tree or fence, or the wind changes after daybreak? Actually, the 

 result one finds is that the moths disappear, and I fully expect they 

 creep away into the grass near the ground, but I have never been 

 able to catch one actually doing so and satisfy myself as to its inten- 

 tions. Moths usually, if undisturbed, pass the whole time between 

 sunrise and sunset without moving, and it would be an experiment 

 of very great interest to locate one at rest on the south side of an 

 exposed tree-trunk on a bright, sunny morning, and keep him under 

 close observation, as the sun worked round until it shone upon him, 

 to see whether he moved away, or the sunlight passed round and left 

 him in the shade again. Unfortunately, the experiment would take a 

 good deal of time in all probability, and if the experimenter relaxed 

 his attention for a few minutes, the anticipated move would be sure 



