Butterflies Worth Knowing

by Clarence Moores Weed

The Yearly Cycle

The yearly cycle in southern New Hampshire may be taken as an illustration of the life of the species in regions where there is but one brood. The butterflies appear in open woods and on cut-over lands in May and June. They lay eggs upon the twigs of oak trees, one egg in a place and generally near a leaf stem. The egg soon hatches into a little caterpillar that crawls upon a near-by leaf and begins the construction of its tubular nest by bending over the margin and sewing it with golden silk. It utilizes this nest chiefly as a tent for resting and sleeping and wanders away from it generally to another leaf when it is ready to feed. It grows very slowly, having before it all the weeks of summer to complete its caterpillar growth. As it gets larger it needs a new tent and is likely to desert its early one. When it does this some observers have noted a curious habit. It cuts loose all the silk that binds the margin of the leaf down upon the blade so that the flap is free to spring back to its original position. It would be difficult to suggest an adequate explanation for this habit.

When autumn comes our caterpillar is faced with the problem of passing through the winter successfully. It must shelter itself from birds, spiders, predaceous beetles, and many other enemies. It must find a means of keeping out of the reach of snow and rain, for while it can survive a great degree of cold as long as it keeps dry, it might easily be killed by freezing up with moisture. But the caterpillar is able to provide against these dangers. It has apparently an abundant supply of liquid silk to secrete from the silk glands in its head, so it lines its tubular tent with a dense silken web that effectually excludes enemies and moisture. It thus has on the outside of its nest the thick oak leaf and on the inside a dense soft lining that makes a most admirable winter protection. So it remains here throughout the winter, the leaf commonly staying on the tree until early spring. Then leaf, nest, and enclosed caterpillar are likely to drop to the ground to remain until spring arrives in earnest. Just what happens then seems to be a bit doubtful. The caterpillar changes to a chrysalis, but whether it first works its way out of its winter nest and makes a new and less dense covering seems not to be certainly known. Here is another good opportunity for some careful observations.

At any rate, the caterpillar changes to a chrysalis, and late in spring it changes again to an adult butterfly that flits about on dusky wing for a few weeks before it dies.

The Sleepy Dusky-wing
Thanaos brizo

The appearance of this butterfly both as to size and marking is very similar to that of Juvenal's Dusky-wing except that the white spots are not present on the front wing of this species. The life-histories of the two species as well as their distribution seem to be closely parallel. The present butterflies are to be found early in summer in the same oak barrens as the other, the blueberry blossoms being freely visited for nectar by both species.

Persius's Dusky-wing
Thanaos persius

This is a rather small, dark brown Skipper, with a few white spots toward the apex of the front wing, but otherwise not marked except for a very pale transverse band which is almost obsolete. The butterfly is found from ocean to ocean along the northern tier of states. It also occurs in the Eastern states as far south as Florida as well as in the states along the Pacific Coast.

The food plants of the caterpillars differ from most of those of the other Skippers. The butterflies lay their yellowish green eggs, one in a place, upon the leaves of willows and poplars. These soon hatch into little caterpillars each of which cuts out a small flap along the margin of the leaf and folds it over, fastening it in place with silken threads. It thus forms a protecting nest within which it remains during the day, going forth at night to a neighboring part of the same leaf or to another leaf, and feeding upon the green surface tissues. In this first caterpillar stage it does not eat the veins to any extent. As it becomes larger it constructs a larger nest and feeds more freely upon the leaf tissues. When about half grown it has the curious habit of biting out small holes here and there in the blade so that the leaf takes on a very unusual appearance. The presence of these holes is generally the easiest way to find the caterpillars, for when the holes are seen, a little searching is likely to show one the characteristic tent-like nest.

After a few weeks the caterpillars become full grown. They then sew themselves in for the winter, fastening all of the crevices in the nest so securely with silken webbing that a very serviceable winter cocoon is formed. An interesting fact is that this sewing up for the winter is likely to take place about midsummer, the caterpillars remaining quiet from this time until the following spring. The nests of course fall in autumn with the leaves and the caterpillars remain unchanged until April or May, when they transform into chrysalids to emerge in May as butterflies. There appears to be normally but one brood a year although there is some evidence of a partial second brood.