Diamondback moths start out life in the form of eggs. Female diamondback moths typically deposit 150 eggs but may deposit as many as 300, placing them in small groups or single increments in the depressions of foliage. The eggs are oval-shaped, vary from pale green to yellow and are 0.44 mm long and 0.26 mm wide. They are extremely difficult to see without a microscope. Development time from egg form to larva typically takes about five and a half days.
Once a diamondback moth egg hatches it becomes a larva -- or caterpillar -- measuring up to 1/3 inch at the end of this stage. Recently hatched larvae are also difficult to spot without a microscope, take on a distinctive green hue with small white patches, wriggle violently if disturbed and sport five pairs of prolegs that protrude from the posterior forming a recognizable "V." Diamondback larvae start the crop damage process, munching on leaves to create a "mine" where the larvae then molt. This phase of life varies from 6 to as many as 30 days.
The pupa instar of the diamondback moth (also called pupation) takes place in a silk cocoon that is yellow, 7 to 9 mm long and deposited on the protected underside of leaves or the florets of plants (such as broccoli and cauliflower). The silky, cocoon-covered pupa phase averages eight and a half days.
As it exits its silky resting place, the pupa emerges as a fully developed diamondback moth. What emerges is a 6-mm-long, slender, grayish-brown moth. Distinguishing characteristics include pronounced antennae, slightly upturned wings (when viewed from the side) and a cream or brown-colored band that contains the notable diamond shape. Adult moths are not capable of flying long distances; rather, they depend on wind to move from plant to plant. Male diamondback moths live an average of 12 days, and females live an average of 16.