s on Looper caterpillars (Known also
as Measuring-worms, Inchworms, Spanworms and Surveyors: the caterpillars
of the Geometrid Moths.--Translator's Note.), has just been reared in
my refectory on Spiders. Replete to the regulation point, it spins its
cocoon. What will emerge from this? If the reader expects to see any
modifications, caused by a diet which the species, left to itself, had
never effected, let him be undeceived and that quickly. The Ammophila
fed on Spiders is precisely the same as the Ammophila fed on
caterpillars, just as man fed on rice is the same as man fed on wheat.
In vain I pass my lens over the product of my art: I cannot distinguish
it from the natural product; and I defy the most meticulous entomologist
to perceive any difference between the two. It is the same with my other
boarders who have had their diet altered.

I see the objection coming. The differences may be inappreciable, for my
experiments touch only a first rung of the ladder. What would happen
if the ladder were prolonged, if the offspring of the Ammophila fed
on Spiders were given the same food generation after generation? These
differences, at first imperceptible, might become accentuated until they
grew into distinct specific characters; the habits and instincts might
also change; and in the end the caterpillar-huntress might become a
Spider-huntress, with a shape of her own. A species would be created,
for, among the factors at work in the transformation of animals, the
most important of all is incontestably the type of food, the nature
of the thing wherewith the animal builds itself. All this is much more
important than the trivialities which Darwin relies upon.

To create a species is magnificent in theory, so that we find ourselves
regretting that the experimenter is not able to continue the attempt.
But, once the Ammophila has flown out of the laboratory to slake her
thirst at the flowers in the neighbourhood, just to try to find her
again and induce her to entrust you with her eggs, which you would rear
in the refectory, to increase the taste for Spiders from generation
to generation! Merely to dream of it were madness. Shall we, in our
helplessness, admit ourselves beaten by the evolutionary effects of
diet? Not a bit of it! One experiment--and you could not wish for a more
decisive--is continually in progress, apart from all artifices, on an
enormous scale. It is brought to our notice by the parasites.

They must, we ar