06/02/2026
Next up in our monarch biology series: Larvae!
The larval stage, or caterpillar stage, comes after a monarch has hatched from its egg and will last for about 10 to 14 days. During this time, the monarch will do all of its growing.
Milkweed is the only plant that a monarch caterpillar will consume (called a "host plant"). As it eats, it'll eventually get too big for its skin and will molt so it can continue eating and growing. A monarch will go through five of these intervals between moltings, called "instars," and will grow from about 2-6 millimeters to about 25-50 millimeters!
While milkweed doesn't appeal to many organisms, it does to monarchs! As a monarch caterpillar eats milkweed, it'll do something extraordinary and sequester some of the toxins in the milkweed within itself. This will make the caterpillar distasteful to many vertebrate predators, creating some protection around the caterpillar at this very vulnerable stage in its development.
To learn more about monarch caterpillar biology, head to our website. Stay tuned for Part 3 in our monarch biology series, where we'll highlight more of the larvae's anatomy!
Photo credit: Donna Barski
