Chewing insects include caterpillars and beetle larvae like Colorado potato beetle and cabbage worms. They are voracious feeders with toothed jaws that tear and mash plant tissue. They can nibble on leaf margins, eat holes in the leaves, or completely defoliate a plant. Most chewing insects go through a complete metamorphosis, changing their appearance several times from the time they hatch until they're adults. Typically they hatch from eggs into larvae, then transform into pupae, before emerging as adults.
Some insects cause severe plant damage only in the larval stage.
When they become adult moths and butterflies, they suck plant nectar and cause no harm. In general, insects are easiest to control during the egg stage. Simply remove eggs from the underside of leaves, where they are usually laid. Since many insects have more than one generation in a season, you'll need to keep your eyes open for eggs throughout the summer. Larvae and nymphs often over-winter in the soil or in plant debris, so garden cleanup is good prevention.