118 THE HUMBLE-BEE VII 
eventually disappearing without having harmed the 
bees. 
Several more of my nests came to grief through 
a sudden and mysterious destruction of the brood. 
In three or four instances the brood was in an 
advanced stage, within a few days of the emergence 
of the workers. The cocoons were torn open, and 
the fragments were scattered about the nest, which 
was in a state of great disorder. I never succeeded 
in catching the assailants at work, but I set traps in 
two of the nests the day after the cocoons had been 
rifled, baiting them with the empty cocoons, and 
caught shrews which I have no doubt were the 
culprits, as these animals are insectivorous, and 
the brood of a humble-bee would make a dainty 
meal for them. In another case I foundie 
field-mouse (Mus sylvaticus) occupying a nest from 
which the cocoons had disappeared.'’ Probably the 
common house-mouse also eats the brood when it 
can get a chance. Field voles (Avvicola agrestis), 
distinguishable from the true mice by their shorter 
tails, stouter bodies, and smaller eyes and ears, were 
common in the neighbourhood of my nests, and 
were sometimes found occupying the empty ones, 
but there was no evidence that they attacked the 
brood. Some of the nests had their material added 
to, others were largely reconstructed, and I| think 
this must have been chiefly the work of voles. 
1 T cannot corroborate Col. Newman’s statement, quoted by Darwin, that 
humble-bees’ nests are more numerous near small towns than in the open 
country, believed to be because the cats in towns keep down the field mice, 
and think that this must be the case only in particular localities. 
