The list of insects that eat the leaves of your vegetables and flowers can be long, depending on where you live. The list grows longer if you include insect larvae. Leaf damage varies: Some insects eat holes or large sections while others create notches and merely suck out the chlorophyll. In the larval stage, some insects eat entire leaves while others bore into them, making them unattractive. If you can't get a glimpse of the insects attacking your plants, you can often identify them from the damage they do.
Adult Leaf-Eating Insects
Many insects that damage leaves do so while in the larval stage, but not all. Those that munch on leaves as adults are usually the hopping or crawling varieties, although some bees cause leaf damage while making their nests.
Grasshoppers (Melanoprus) have large, hinged hind legs and and cylindrical, 1-inch-long bodies. Of the more than 100 species, those you're likely to find in your garden include:
- Red-legged grasshopper (Melanoprus femurrubrum) lives all over North America but prefers moist climates. This species becomes a problem in large numbers.
- Two-striped grasshopper (Melanoprus bivitattus) has two distinctive yellow stripes on its back. This grasshopper is found throughout North America except in the Southeast and Southwest.
- Differential grasshopper (Melanoprus differentialis) has a herringbone pattern on most of its body. This species lives in regions of lush vegetation throughout North America.
Grasshoppers have strong teeth and chew large holes in leaves. They eat leaves on most vegetable plants and may also eat the fruit.
Slightly less than 1/2 inch long, oval and sporting metallic green and brownish wing covers, Japanese beetles (Popillia japonica) were introduced to the U.S. and thrive in the eastern part of the country. When they feed on the leaves of common garden plants, they favor the soft tissue between the main leaf arteries, in effect "skeletonizing" the leaves.
About 1/16 inch long and either black or tan, flea beetles belong to the family Chrysomelidae and are able to jump, like fleas. They affect a variety of common plants and flowers, chewing them in a characteristic pattern of small holes, known as "shotgunning."
The aphid subfamily family, Aphididae, includes more than 1,000 species, and about 250 of these can cause plant damage. Aphids are small, soft-bodied insects that suck juices from leaves, and they live in every part of North America. They collect on the undersides of leaves -- especially new ones -- and excrete a sticky substance known as honeydew that often attracts other insects, including ants. Leaf damage includes curling, stunting and yellowing.
Like aphids, thrips -- order Thysanoptera -- are tiny insects, each one less than 1/20 inch long. They congregate by the hundreds on the undersides of plant leaves, sucking the juices from the leaves and leaving a varnishlike coating. Some thrips species, such as the bean thrips (Caliothrips fasciatus), attack specific plants, while others are not as choosy. Any plant in your garden could suffer a thrips infestation.
Black Vine Weevils
Adult black vine weevils (Otiorhynchus sulcatus) chew large chunks from leaves, leaving crescent-shaped notches, but the larvae of these 1/2-inch slate-colored insects do the most damage by attacking roots and bark. Identifying the adults, which live throughout the northern U.S. and parts of Canada, are a warning to treat the soil to eradicate the larvae. Black vine weevils prefer rhododendrons (Rhododendron spp.), which grow as perennials in U.S. Department of Agriculture plant hardiness zones 4 through 9, and yews (Taxus spp.), which are perennial in USDA zones 4 through 8.
Mexican Bean Beetles
Found on the leaves of most varieties of beans (Phaseolus spp.), Mexican bean beetles (Epilachna varivestis) are relatives of ladybugs, but are yellow rather than orange. They thrive in the eastern part of the U.S. from Florida to the Canadian border. Both the adult and larvae feed on leaves, skeletonizing them.
Leafcutter bees (Megachile spp.) don't eat leaves. Instead, they cut out semicircular sections and use these to make their nests. The bees, which are about the size of honeybees, are native to North America and are important pollinators. They are not aggressive and have a mild sting.
Some insects do more damage to leaves in their larval stage than they do as adults. These larvae look like grubs, caterpillars or tiny slugs. They include:
- Parsley worm, the caterpillar of the swallowtail butterfly, is a 2-inch green caterpillar with black stripes and yellow and orange dots. It prefers the leaves of plants belonging to the carrot family, especially annual parsley (Petroselinum crispum).
- Tomato hornworm has a distinctive hornlike tail. This large greenish caterpillar, the larva of a sphinx moth, can strip all the leaves from a plant. It prefers plants of the nightshade family, especially tomatoes (Lycopericon esculentum).
- Leaf miners are the larvae of various moths and flies that have the habit of burrowing inside leaves. This usually creates large blotches on the surfaces of the leaves. These tunnels normally don't harm the plants.
- Sawfly larvae secrete a slimy substance, so you might mistake them for slugs. After hatching, they feed on the soft undersides of leaves.