abound in prodigious numbers, and take no precautions to conceal
themselves, even when at rest, during the night. Mr. Bates (the author of
the very interesting work "The Naturalist on the River Amazons," and the
discoverer of "Mimicry") found that these conspicuous butterflies had a
very strong and disagreeable odour; so much so that any one handling them
and squeezing them, as a collector must do, has his fingers stained and so
infected by the smell, as to require time and much trouble to remove it.

It is suggested that this unpleasant quality is the cause of the abundance
of the Heliconidae; Mr. Bates and other observers reporting that they have
never seen them attacked by the birds, reptiles, or insects which prey upon
other lepidoptera.

Now it is a curious fact that very different South American butterflies{30}
put on, as it were, the exact dress of these offensive beauties and mimic
them even in their mode of flight.

In explaining the mode of action of this protecting resemblance Mr. Wallace
observes:[25] "Tropical insectivorous birds very frequently sit on dead
branches of a lofty tree, or on those which overhang forest paths, gazing
intently around, and darting off at intervals to seize an insect at a
considerable distance, with which they generally return to their station to
devour. If a bird began by capturing the slow-flying conspicuous
Heliconidae, and found them always so disagreeable that it could not eat
them, it would after a very few trials leave off catching them at all; and
their whole appearance, form, colouring, and mode of flight is so peculiar,
that there can be little doubt birds would soon learn to distinguish them
at a long distance, and never waste any time in pursuit of them. Under
these circumstances, it is evident that any other butterfly of a group
which birds were accustomed to devour, would be almost equally well
protected by closely resembling a Heliconia externally, as if it acquired
also the disagreeable odour; always supposing that there were only a few of
them among a great number of Heliconias."

"The approach in colour and form to the Heliconidae, however, would be at
the first a positive, though perhaps a slight, advantage; for although at
short distances this variety would be easily distinguished and devoured,
yet at a longer distance it might be mistaken for one of the uneatable
group, and so be passed by and gain another day's life, which might in many
cases be sufficien