Height:  1.2 mm   Width:  0.9 mm
Appearance:  Monarch eggs are usually attached to the underside of young milkweed leaves.  They are laid singly, and it is uncommon (though not unheard of) to find more than one on a single plant.  The eggs look off-white or yellow, and are marked with a series of longitudinal ridges.  The hard outer shell, or chorion, protects the developing larva.

First Instar

Body length:  2 to 6 mm
Body width:  0.5 to 1.5 mm
Front tentacles:  Small bumps
Back tentacles:  Barely visable
Head capsule:  0.6 mm in diameter

Appearance:  A newly-hatched monarch larva is pale green or grayish-white, shiny, and almost translucent.  It has no stripes or other markings.  The head looks black, with lighter spots around the antennae and below the mouthparts, and may be wider than the body.  There is a pair of dark triangular patches between the head and front tentacles which contain setae, or hairs.  The body is covered with sparse setae.   Older first instar larvae have dark stripes on a greenish background.

After hatching, the larva eats its eggshell (chorion).  It then eats clusters of fine hairs on the bottom of the milkweed leaf before starting in on the leaf itself.  It feeds in a circular motion, often leaving a characteristic, arc-shaped hole in the leaf.  First (and second) instar larvae often respond to disturbance by dropping off the leaf on a silk thread, and hanging suspended in the air.

Second Instar

Body length:  6 mm to 9 mm
Body width:  1 to 2 mm
Front tentacles:  0.3 mm
Back tentacles:  Small knobs
Head capsule:  0.8 mm diameter

Appearance:  Second instar larvae have a clear pattern of black (or dark brown), yellow and white bands, and the body no longer looks transparent and shiny.  An excellent characteristic to use in distinguishing first and second instar larvae is a yellow triangle on the head and two sets of yellow bands around this central triangle.   The triangular spots behing the head do not have the long setae present in the spots on the first instar larvae.  The setae on the body are more abundant, and look shorter and more stubble-like than those on first instar larvae.