Make a drawing of the lateral aspect of the whole body.

Life-history and habits.—The tiny, conical, yellowish-green eggs of the monarch butterfly are deposited on the under side of the leaves of milkweeds (Asclepias) and when examined under the microscope are seen to be very beautiful little objects finely ribbed with longitudinal and transverse striæ. The eggs are laid in April and May (depending on the latitude and season) by females which have hibernated in the adult condition. From the eggs the minute, cylindrical, pale-green, black-headed larvæ hatch in four or five days. As soon as hatched the larva devours the eggshell from which it has escaped and then feeds voraciously on the milkweed leaves. It grows rapidly, and in three or four days a blackish band or ring appears on each segment, and for the rest of its life it is very conspicuously colored with its black rings on a yellowish-green background. It molts three times, and in from twelve to twenty days is ready to pupate, or change to a chrysalis.

When ready to pupate the larva usually leaves the milkweed plant, and seeks some such protected place as the under side of a fence-rail or jutting rock. Here it attaches its posterior extremity by a small silken web to the rail or rock, and casting its larval skin appears as a beautiful pale-green chrysalis with ivory black and golden spots. It hangs motionless, and of course without taking food, for from a week to two weeks (according to season and temperature), when the pupal cuticle breaks and the great red-brown butterfly (fig. [165]) issues.

The butterfly feeds (as is indicated by the structure of its mouth-parts) very differently from the larva; it sucks up by means of its long tubular proboscis the nectar of flowers, nor does it confine itself at all to the flowers of milkweeds. It is a fine flyer and a great traveller. Many thousands of these butterflies often make long flights or migrations together. At other times tens of thousands of these butterflies congregate in a certain limited area, clinging sometimes to the branches of a few trees in such numbers and so closely together as to give the tree a brown color. Such a "sembling" of monarch butterflies occurs every year near the Point Pinos lighthouse on the Bay of Monterey, California. The object of this assembling together is not understood. Both the larvæ and adults of the monarch butterfly are distasteful to birds, by their possession of an acrid body-fluid. The species is thus protected against the most dangerous enemies of butterflies, a fact which chiefly accounts for the great abundance and wide distribution of the monarch (see p. [137]). For a full account of the life-history of the monarch butterfly, see "Scudder's Life of a Butterfly."

LARVA OF MONARCH BUTTERFLY (Anosia plexippus)

Technical Note.—For directions for finding and identifying the larvæ of the monarch butterfly see p. [171]. If larvæ (caterpillars) of Anosia cannot be found, those of any other butterfly or moth will do. Use naked, smooth kinds like cutworms, cabbage worms and the like, rather than hairy or spiny ones. Use large specimens. Kill the caterpillar with ether or in a cyanide bottle.

Structure (fig. [44]).—As we have learned from the study of the life-history of the locust, water-beetle and butterfly, some insects are hatched from the egg in a condition resembling that of the parents in most structural characters. This is true of the locust. Other insects, as the beetle and butterfly, are hatched in a form and condition apparently very different from that of the parents. The external appearance of a beetle or butterfly larva differs much from that of the adult or imago of the same individual. It will be of interest to examine more particularly the structural condition of one of these larvæ and to compare it with the structure of the adult.

Fig. 44.—Dissection of the silkworm, larva of the moth Bombyx mori.