lies Sesiidae and Aegeriidae, many of
which resemble bees, wasps, ichneumons, or saw-flies, and have received
names expressive of the resemblance; and the parasitic flies (Volucella)
which closely resemble bees, on whose larvae the larvae of the flies
feed.

The great bulk of such cases remained, however, unnoticed, and the
subject was looked upon as one of the inexplicable curiosities of
nature, till Mr. Bates studied the phenomenon among the butterflies of
the Amazon, and, on his return home, gave the first rational explanation
of it.[98] The facts are, briefly, these. Everywhere in that fertile
region for the entomologist the brilliantly coloured Heliconidae abound,
with all the characteristics which I have already referred to when
describing them as illustrative of "warning coloration." But along with
them other butterflies were occasionally captured, which, though often
mistaken for them, on account of their close resemblance in form,
colour, and mode of flight, were found on examination to belong to a
very distinct family, the Pieridae. Mr. Bates notices fifteen distinct
species of Pieridae, belonging to the genera Leptalis and Euterpe, each
of which closely imitates some one species of Heliconidae, inhabiting
the same region and frequenting the same localities. It must be
remembered that the two families are altogether distinct in structure.
The larvae of the Heliconidae are tubercled or spined, the pupae
suspended head downwards, and the imago has imperfect forelegs in the
male; while the larvae of the Pieridae are smooth, the pupae are
suspended with a brace to keep the head erect, and the forefeet are
fully developed in both sexes. These differences are as large and as
important as those between pigs and sheep, or between swallows and
sparrows; while English entomologists will best understand the case by
supposing that a species of Pieris in this country was coloured and
shaped like a small tortoise-shell, while another species on the
Continent was equally like a Camberwell beauty--so like in both cases
as to be mistaken when on the wing, and the difference only to be
detected by close examination. As an example of the resemblance,
woodcuts are given of one pair in which the colours are simple, being
olive, yellow, and black, while the very distinct neuration of the wings
and form of the head and body can be easily seen.

[Illustration: FIG. 23.--Methona psidii (Heliconidae). Leptalis orise
(Pieridae).]

B