LIFE-HISTORY OF THE HERB ROBERT 103 
Lastly, there is the Great Yellow Slug,* that does 
not as a rule care about fresh food, but prefers high 
game, so I was not surprised at finding that he left 
his rations alone, until I supplied him with some 
leaves that were decaying, and this of course would 
not be harmful to the plant. 
It should be borne in mind by any one who makes 
experiments with slugs in captivity that, being devoid 
of the protective shell into which the snail retires, 
they must be kept moist, otherwise they will dry up 
and die even when supplied with suitable food, with 
the result that one may be misled into attributing 
death to poisoning instead of to drought. 
Again, I have far too many woodlice; I did not 
expect them to eat the leaves, for they like succulent 
fruits and petals as well as the same sort of nasty 
food as the Yellow Slug, but I was not prepared to 
find them all dead the next morning. 
Indeed, I was so surprised that I put a few into a 
moist box without food and a few more into one with 
some of the leaves, with the result that the former 
lived for three days, when I released them, whereas 
the latter died the same night : so it is possible that the 
leaves give off fumes that are fatal to these creatures. 
I may add that I took similar precautions with a 
view to eliminating possible sources of error in my 
other experiments, and that it is imperative always 
to do so, however troublesome it may be. 
I turned next to the caterpillars. One night I saw 
one of a Yellow-underwing on a leaf which was not 
quite whole. I did not catch it in the act of nibbling, 
and I meant to secure it in order to find out the 
truth: unfortunately I dropped it and could not find 
* Limaz flavus. 
