e other hand, may have as many
as eight pairs of pro-legs, the series beginning on the second abdominal
segment; here, however, the pro-legs have no hooklets. Among the
Lepidoptera, we notice a reduction in the number of pro-legs in the
'looper' caterpillars of Geometrid moths. Here only two pairs are
present, those on the sixth and tenth abdominal segments. Consequently,
as the caterpillar can cling only by the thorax and by the hinder region
of the abdomen, the middle region of the body is first straightened out
and then bent into an arch-like form, as the insect makes its progress
by alternate movements of stretching and 'looping.'

[Illustration: Fig. 17. _c_, Ruby Tiger Moth (_Phragmatobia
fuliginosa_); _a_, caterpillar; _b_, cocoon. After Lugger, _Insect
Life_, vol. II.]

Caterpillars, with their relatively soft bodies, feeding openly on the
leaves of plants, are exposed to the attacks of many enemies, and the
various ways in which they obtain protection are well worth studying. A
clothing of hairs[7] or spines is often present, and it is interesting
to find that many species of our native Tiger and Eggar Moths (Arctiadae
and Lasiocampidae) which pass the winter in the larval stage, have
caterpillars with an especially dense hairy covering (fig. 17).
Experiments have shown that hairy and spiny insects are distasteful to
birds and other creatures that prey readily on smooth-skinned species, a
conclusion that might well have been expected. Certain smooth
caterpillars however appear to be protected by producing some nauseous
secretion, which renders them unpalatable. Many of these, as the
familiar cream yellow and black larva of the Magpie Moth (_Abraxas
grossulariata_), are very conspicuously adorned, and furnish examples of
what is known as 'warning coloration,' on the supposition that the gaudy
aspect of such insects serves as an advertisement that they are not fit
to eat, and that birds and other possible devourers thus learn to leave
them alone. On the other hand, smooth caterpillars which are readily
eaten by birds are usually 'protectively' coloured, so as to resemble
their surroundings and remain hidden except to careful seekers. Many
such caterpillars are green, the upper surface, which is naturally
exposed to the light, being darker than the lower which is in shadow.
When the caterpillar is large, the green area is often broken up by pale
lines, longitudinal as on the larvae of many Owl Moths (Noctuidae) o