The Descent of Man

worker-bees is a much more difficult case, but I
have endeavoured to shew in my 'Origin of
Species,' how these sterile beings are subjected
to the power of natural selection.)
Mutilla Europaea makes a stridulating noise;
and according to Goureau (62. Quoted by
Westwood, 'Modern Classification of Insects,'
vol. ii. p. 214.) both sexes have this power. He
attributes the sound to the friction of the third
and preceding abdominal segments, and I find
that these surfaces are marked with very fine
concentric ridges; but so is the projecting thoracic
collar into which the head articulates, and
this collar, when scratched with the point of a
needle, emits the proper sound. It is rather surprising
that both sexes should have the power
of stridulating, as the male is winged and the
female wingless. It is notorious that Bees express
certain emotions, as of anger, by the tone of
their humming; and according to H. Muller (p.