Here's What's Eating Your Garden: 13 Common Leaf-Eating Garden Pests
A Quick and Accurate Guide to Leaf-Eating Garden Pests
Anyone with a garden knows that for every kind of plant, there's an insect or an animal that eats it. From flowers to fruit trees, everything that grows hosts a number of insects and other organisms that feed on it. If you have noticed something eating holes in your leaves, or even eating the entire leaf, then this quick guide will help you understand who—and what—you and your garden are up against.
Slugs are shell-less snails—actually a kind of land-based mullosk—and they're responsible for some serous garden destruction, especially if their population gets out of hand. They are most common in damp, shady places, and feed on leaves at night—in fact, one of the best ways to tell if you have a slug infestation is to go out with a flashlight and have a look. They often feed underneath the leaf, and they always leave a slime trail wherever they go.
Slug feeding damage presents as holes in leaves between a 1/4th to 1 inch in diameter. They don't start eating at the edge of the leaf, like caterpillars and sawflies, but go right for the middle. They seem to prefer hostas, but will attack virtually anything with leaves. Slugs will also go for fruit that is touching the ground, especially melons and strawberries.
- What They Are: Invertebrates, related to snails.
- How to Tell: Small-to-medium-sized holes in the middle of the leaf; slime trails.
- What to Do: One tried and true method to control slugs is to leave open containers of beer or soapy water out on the ground. Many of the slugs will go for a drink or a bath and drown.
2. Sawfly "Caterpillars"
Sawfly larvae look and act a lot like caterpillars—in fact, to many gardeners, the difference is academic, since the damage they do to leaves is comparable. But it's worth knowing that these garden pests don't grow up to be butterflies or moths. Instead they become a stingless little wasp called a "sawfly." They are in the insect order Hymenoptera, along with bees, ants, and stinging wasps. They do not form a nest but live as solitary individuals.
Most people never notice the adult sawfly, but if you have sharp eyes and know what to look for, you will see them flying around the affected plants; this is a good way to diagnose the infestation. The larvae are different from caterpillars in that they do not grasp with their hind legs, but instead curl them up, often over their heads, forming an "S" shape.
The wasp is called a "sawfly" because the female "saws" a cut in twigs and branches, into which she deposits her eggs. In bad infestations, these cuts can themselves weaken a tree or plant.
Another characteristic of a sawfly infestation is that they occur in groups, and feed openly during the day—they do not hide, and are not camouflaged. The most common host plants are dogwood, willow, rose, and pine species.
- What They Are: The larva of a stingless wasp.
- How to Tell: Many "caterpillars" feeding on dogwood or willow, in a group, with their rear ends held in a curve above their heads.
- What to Do: You can pick them off fairly easily and drop them in a bucket of soapy water to kill them. If there are too many, diatomaceous earth is a good solution.
Cutworms are good-sized moth caterpillars that hide in the soil during the day and come out to feed at night. They get their common name from the way that some species specialize in eating the stems of plants just above the soil line, causing healthy plants to topple over.
A cutworm infestation can seem like a slug problem, except cutworms typically eat the edge of the leaves, not the middle, and they do not leave a slime trail. They can be very hard to catch in the act, since they only feed during the night, and are well-camouflaged as they hide by day among the dirt and debris in a garden bed.
The best way to control cutworms, as with many garden pests, is with diatomaceous earth. This is an all-organic, non-chemical substance made from the fossilized remains of tiny creatures called diatoms; the jagged silicon shells damage the outer "skin" of crawling insects, killing them.
- What They Are: Cutworms are the larvae of brown moths, often called "darts."
- How to Tell: Damage to leaves with no apparent cause; plants that topple over from having their stems "cut" by the feeding caterpillars.
- What to Do: Dust with diatomaceous earth.
4. Cabbage White Butterfly Caterpillars
This insect is one of the most prevalent pests of backyard gardens. It's range is nearly world-wide, and its hosts plants are basically anything you decide to grow. The adult butterfly is a plain white number that nearly everyone has seen fluttering around flowers and plants—and that's your first sign that you have a problem.
Female cabbage whites lay tiny, conical eggs on the underside of leaves. The caterpillar hatches out, eats the empty eggs shell, and then starts eating everything else. Holes in your kale, cabbage, broccoli, spinach, chard, and so on are almost always the work of the cabbage white caterpillar.
You can look for them, but more often that not you won't see them, for the simple reason that they're nearly invisible: their color and design blends in with the leaves to a ridiculous degree. This is doubtless one of the main reasons they're so successful as a species.
If you do find them, you can pick them off. But you will miss as many as you find, so your best options are to either dust with diatomaceous earth, or place netting over your plants.
- What They Are: A butterfly species whose caterpillars eat everything.
- How to Tell: Big holes in the leaves of many different plants.
- What to Do: Dust or netting may protect your plants.
Grasshoppers are an often-overlooked source of damage to garden plants, especially in the late summer. If your garden is a little wild—and whose isn't, come September—then it's a good possibility that grasshoppers are contributing to the damage you see in your leaves.
Yes, grasshoppers (and their relatives, crickets and katydids) eat leaves. Many species come out at night to feed on the leaves of many kinds of plants. And they can eat a lot, too—these are the same insects as the “locusts” you hear about everywhere from the Bible to the Dust Bowl.
Grasshoppers undergo incomplete metamorphosis, which means that baby grasshoppers look like grown-ups, only smaller. They eat and grow, shedding their skin along the way, and by late summer they're big, with well-developed wings that assist their long leaps from plant to plant.
- What They Are: An insect in the order Orthoptera.
- How to Tell: Grasshoppers leave irregular, "ragged" looking holes in leaves.
- What to Do: As with other flying/jumping pests, diatomaceous earth or protective netting are possible solutions.
6. Japanese Beetles
You’ll see these little insects buzzing around your roses and many other plants (over 200 different plant species are on the menu). They mimic bees, which may protect them from birds, but they're an invasive beetle species from Asia that has been wreaking havoc across North America for most of the century. The problem isn’t identifying them; the problem is getting rid of them. Since they’re and invasive species, they have few to none natural predators here in North America.
Japanese beetles feed and fly right out in the open, so you'll know if you have them. They chew up everything, from leaves to flowers—they're especially fond of rose blossoms. Controlling them is notoriously difficult—you can pick them off, but more come, seemingly out of nowhere. Fortunately there is a disease called "milky spore" that kills them in the larval stage (grubs that live underground). You can buy milky spore at garden supply spots; it's about the only option for this pest.
- What They Are: A bright green-gold beetle that flies like a bee.
- How to Tell: You will see them all over your plants.
- What to Do: Milky spore is a commercially available agent that kills the larvae.
Hornworms are huge caterpillars that can often be found chowing down on your tomato plants. They are among the most voracious eaters in the animal kingdom, and just a few can decimate your tomato crop. They almost always occur in groups, so a hornworm infestation is a serious problem indeed.
Hornworms are the larvae of a big brown moth called a "hawk moth." There are many different kinds other than the tomato-eating variety, and some are quite beautiful (check out the lovely oleander hawk moth for an example). They begin as tiny eggs and tiny immature larvae the size of a pencil lead, but before long are as big as a hot dog. Despite their size, they are very hard to spot on a plant.
If your tomatoes are showing signs of serious defoliation, and there are holes in the green fruit, then you almost certainly have hornworms. Hunting for them and picking them off will help, but to really get rid of them you will need to dust with diatomaceous earth. These caterpillars are also susceptible to being parasitized by a kind of wasp that lays its eggs on the caterpillar; the wasps larvae eat the living caterpillar's fat stores, then burrow out and spin little cocoons on its skin. The caterpillar invariably dies.
- What They Are: Huge green caterpillars that eat a lot of tomato leaves.
- How to Tell: Missing leaves and stems; holes in fruit.
- What to Do: Dust with diatomaceous earth.
Aphids are tiny insects that occur in large colonies. They suck the plant's sap and vital juice, and when there are enough of them they can easily kill the entire plant. They're related to cicadas, which are essentially giant, singing aphids.
Aphids are attended by ants, who "milk" them for a drop of sweet honeydew the aphids produce from their hind end; in return, the ants drive off or kill other insects that prey on the aphids. Fortunately, there is one insect that ants can protect them from: lady bugs. These brightly spotted beetles feed on aphids as both larvae and adults. You can buy lady bug cultures from gardening supply stores, and they can be quite effective in controlling the pests.
If you have aphids on your plants, you will often find naturally occurring lady bug beetles and their larvae—which look like tiny gila monster lizards—hanging around, feeding on them. But buying more may help the situation!
- What They Are: Tiny green or gray insects that occur in large colonies.
- How to Tell: Masses of small insects around the top leaves of a plant; wilting leaves and stems.
- What to Do: Encourage the activities of lady bug beetles; consider buying a commercial culture.
9. Leafcutter Ants and Bees
These insects are rarely a major problem except in the far South, where leafcutter ants can strip an entire small tree of all of its leaves in a matter of a few days. If you have leafcutter ants you will certainly know it—what to do about them is another matter. They are notoriously hard to control.
Leafcutter bees, on the other hand, can be found across North America. They cut nearly perfect circles from the edges of leaves, and use the material to help feed their young. It's unusual for leafcutter bees to cause enough damage to truly matter, and controlling them is nearly impossible. But if you have noticed geometrically accurate circles being carved from your leaf margins, then it's most likely the work of leafcutter bees.
- What They Are: Bees and ants that cut up leaves for their nests.
- How to Tell: Large numbers of ants carrying away pieces of leaf; or small circular bite taken from leaf edges.
- What to Do: There are few good solutions for these insects.
10. Asparagus Beetles
This pest is very host-specific; that is, it only eats asparagus. But it can do some damage if the numbers get out of control, and so are worth knowing about.
You'll know you have asparagus beetles if you see them and/or their fat, grubby little larvae hanging out on your asparagus plants, mainly in the summer after the plants have grown into tall, feathery "bushes." The cool thing about them is that there are two distinct kinds, and they always occur together: one is orange with black dots, and the other is black with a light-colored "t" on its back.
Asparagus beetles start feeding in early summer, and undergo several generations as the summer goes on and the plant grows. They are generally just a nuisance, but in large numbers they can seriously damage your crop.
This beetle has a few natural predators, including a parasitic wasp that lays eggs on the larvae, with the wasp larvae eating the grub from the inside out (this is the same mechanism as the wasp that attacks horn worms and other caterpillars). Other natural control methods include lady bug beetles and lacewings; you may try using a culture from a garden supply center. There are also nematode (worm) cultures that you can introduce to the soil around your plants that may help control asparagus beetles.
- What They Are: Small beetles that eat only asparagus.
- How to Tell: You will see the brightly colored beetles on the plants.
- What to Do: There are many good botanical solutions for these pests.
11. Black Swallowtail Caterpillars
I hate to characterize this beautiful butterfly species as a "pest," but some gardeners may see it that way. Black swallowtails are common throughout North America, with several subspecies, forms, and related species occurring everywhere from the desert southwest to the pine forests of Maine. The immature larvae of these insects are all very similar, and are often noticed by gardeners. They occur on dill, parsley, and carrot, and resemble bird droppings with their overall black coloration and light-colored "saddle" marking.
The adult butterfly is beautiful, with velvet black wings marked with yellow and blue. You will often see them visiting flowers in your garden, as well as laying eggs on the food plant.
- Does it sting? No, this caterpillar is harmless.
- What does it eat? Carrots, parsley, dill, and related plants.
- Will it seriously damage plants or trees? No.
- Is it rare? No, although the adult is more often seen than the black caterpillar.
- What does it turn into? A bright, beautiful butterfly.
- Can you raise it to an adult? Yes.
Bagworms are caterpillars, and they have a very unusual life-cycle. The caterpillars never leave the shelter that they construct, and the females don't even leave as adults -- they are wingless, and die after mating and laying eggs -- all within the confines of the bag shelter. Male moths are small and furry with clear wings. They are very seldom seen.
You will know without a doubt if you have a bagworm infestation. The oval bags, dangling from leaves and branches, are very hard to miss. Bagworm infestations can kill a small tree, but fortunately they are quite easy to control: just pick them off by hand and drop them in a bucket of soapy water, or smush them into your compost pile. Bagworms do not sting or bite, and have no other defenses other than retreating to the safety of their bag shelter.
- What They Are: Moth caterpillars that live in bag-like shelters on trees
- How to Tell: You will see the bags hanging from your tree
- What to Do: Simply pick them off and dispose of them.
And finally, a non-insect pest of backyard and commercial gardens: bunny rabbits. Rabbits are becoming increasingly common in urban areas, which puts backyard gardens at risk. Rabbit damage is pretty obvious—they eat everything, and a lot of it—and you can protect your plants by putting up rabbit fence or caging.
The following sources were used for this guide:
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.