While students are raising monarchs and collecting growth data, they observe a range of behavior in larvae and adults. The larva are visible inside the egg just prior to hatching, and they are most easily observed under magnification in the first instar (first stage of larval development). As the larvae grow, students can study movement, feeding behavior, food choice, feeding patterns on leaves, and molting. Behavior of younger and older larvae can be compared if detailed descriptions and records are kept throughout the life cycle. Students can also observe the transitions from larva to chrysalis and the emergence of adult butterfly from the chrysalis. Adult behavior can be observed briefly before the butterflies are released.

Children begin by making brief, superficial observations of behavior, often casting it in human terms. For example, they describe the larva as "tired." They later write detailed descriptions of feeding, molting and movement. For example, they may describe how much the larva has eaten in a certain amount of time, or the pattern of feeding on a leaf.