A RURAL IMPOSTOR. 
35 
veloped into a pointed projection of the form of one tooth of 
the serrate sweet fern leaf. The repetition of the projections 
along the whole length of the caterpillar’s body has rendered 
the resemblance to the leaf as a whole very striking. You will 
notice also that the head is small and angular, making a sug¬ 
gestive tip to the counterfeit leaf, while the underside of the 
body is flattened and the legs are inconspicuous. 
The color of the caterpillar also helps it out in its mimicry of 
the leaf. The foliage of the sweet fern is dull green or light 
rusty brown, there being nearly always many leaves of the latter 
hue upon the plant. The caterpillar is generally of this brown¬ 
ish color, although the precise tint varies considerably. 
If these sham leaves were constantly moving about, their 
shape and their color would profit them little. For birds know 
that true leaves do not wander from place to place upon a 
plant, and a bird seeing such a wanderer would be likely to 
peck at it to see what it is made of. Now to a caterpillar a 
peck is as bad as a swallow: if its skin is pierced its day’s work 
is done. So you will find when you keep your caterpillar under 
observation that it will assume a certain position and remain 
rigid and quiet by the hour, apparently sleeping through the 
day. After the friendly shades of night have fallen it will pro¬ 
bably wander about and feed freely upon the foliage, for then 
it is safe from observation by the eager eyes of the birds. But 
when day returns it will again become quiet. 
The position commonly assumed by this caterpillar is to take 
hold of the stem with the pair of feet at its posterior end, and 
to hold the body rigidly out at the same angle that the leaves 
make in their attachment to the stem. Very often the position 
involves such a resistance to the force of gravity that you won¬ 
der how the insect keeps its front end in position for so long a 
time. If you look carefully; however, with a lens or reading 
glass you can see a silken thread extending from the mouth to 
the twig ; this is the secret of the fixed position, for this thread 
holds the head in place. 
How did this wonderful adaptation come about ? Not so 
