In its manner of laying eggs this butterfly differs from most others.
The great majority of our familiar species lay their eggs one in a
place or possibly two or three near together. Some species deposit
several in a group, while some, like the Mourning-cloak, may lay two
or three dozen in a cluster. Very few, however, deposit hundreds in a
bunch. Two of these are the Baltimore and this American
Tortoise-shell. In the case of the latter the eggs are loosely laid,
hundreds together, upon the leaves of the common stinging nettle.
Probably each female can deposit six or eight hundred eggs. In less
than a week the eggs hatch into minute blackish caterpillars that feed
upon the tender tissues of the leaf upon which they were born and then
migrate together toward the top of the plant. In their habits they are
quite similar to the caterpillars of the Mourning-cloak. As each walks
it spins from its mouth a silken thread and the combined effect of
hundreds of these threads is to make a noticeable silken web over the
leaves. The caterpillars remain in colonies, feeding together from day
to day and gradually denuding the upper branches of the nettle plant,
leaving an unsightly silken web as a memento of their presence. This
webbing is very suggestive of the similar result left behind by a
colony of Mourning-cloak caterpillars upon the twigs of elm or poplar.
When about half grown these caterpillars are likely to scatter more or
less in accidental groups which may make small shelter tents from the
larger leaves. In each little nest there may be four or five or more
of the dark-colored caterpillars. From these shelter tents they sally
forth to feed upon the adjacent leaves and a little later become full
grown as caterpillars. Each now wanders away and finding such shelter
as it is able to, spins a button of silk and becomes a chrysalis. It
remains in this condition but a short time before it emerges again as
the beautiful butterfly.
This species is commonly reputed to have three broods a year,
hibernating both as a butterfly and as a chrysalis. It has been
suggested, however, by Mr. W. F. Fiske, one of our most painstaking
entomologists who has studied the butterflies of New Hampshire for
many years, that it is more probably double-brooded with a period of
aestivation during the later weeks of summer. This seems a very
probable condition and it is to be hoped that some observer will make
such a careful study of this species as to settle the point
definitely.
In the case of many butterflies the distribution of the species
coincides with the distribution of the food plant. This American
Tortoise-shell, however, is perhaps the exception that may prove the
rule, for its southward limit is far north of the southern range of
the stinging nettle. Evidently, it is a species which has developed in
adjustment to the cool climate of northern regions or high altitude,
and it does not easily adapt itself to a warmer territory.
Public-domain text, read in full here on John Shaqi.
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