In general it may be said that mimetic butterflies are comparatively rare
species, but there are exceptions, for instance Limenitis archippus in
North America, of which the immune model (Danaida plexippus) also occurs in
enormous numbers.

In another mimicry-category the imitators are often more numerous than the
models, namely in the case of the imitation of DANGEROUS INSECTS by
harmless species. Bees and wasps are dreaded for their sting, and they are
copied by harmless flies of the genera Eristalis and Syrphus, and these
mimics often occur in swarms about flowering plants without damage to
themselves or to their models; they are feared and are therefore left
unmolested.

In regard also to the FAITHFULNESS OF THE COPY the facts are quite in
harmony with the theory, according to which the resemblance must have
arisen and increased BY DEGREES. We can recognise this in many cases, for
even now the mimetic species show very VARYING DEGREES OF RESEMBLANCE to
their immune model. If we compare, for instance, the many different
imitators of Danaida chrysippus we find that, with their brownish-yellow
ground-colour, and the position and size, and more or less sharp limitation
of their clear marginal spots, they have reached very different degrees of
nearness to their model. Or compare the female of Elymnias undularis with
its model Danaida genutia; there is a general resemblance, but the marking
of the Danaida is very roughly imitated in Elymnias.

Another fact that bears out the theory of mimicry is, that even when the
resemblance in colour-pattern is very great, the WING-VENATION, which is
so constant, and so important in determining the systematic position of
butterflies, is never affected by the variation. The pursuers of the
butterfly have no time to trouble about entomological intricacies.