Darwin, and often quoted for its striking and almost
eccentric character. It is now well known that many flowers require to
be fertilised by insects in order to produce seed, and this
fertilisation can, in some cases, only be effected by one particular
species of insect to which the flower has become specially adapted. Two
of our common plants, the wild heart's-ease (Viola tricolor) and the red
clover (Trifolium pratense), are thus fertilised by humble-bees almost
exclusively, and if these insects are prevented from visiting the
flowers, they produce either no seed at all or exceedingly few. Now it
is known that field-mice destroy the combs and nests of humble-bees, and
Colonel Newman, who has paid great attention to these insects, believes
that more than two-thirds of all the humble-bees' nests in England are
thus destroyed. But the number of mice depends a good deal on the number
of cats; and the same observer says that near villages and towns he has
found the nests of humble-bees more numerous than elsewhere, which he
attributes to the number of cats that destroy the mice.
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