Caterpillars, as every schoolchild knows, eventually turn into butterflies and moths. And who doesn't want butterflies in the garden? They're beautiful, and they're excellent pollinators. But unfortunately, in their youthful stage, these butterflies-to-be are some of the most destructive pests in the vegetable garden. Some varieties of caterpillar eat tree foliage, also. This article offers some advice to identifying signs of caterpillar infestations, and how to control and get rid of them, using non-toxic methods.
There are literally thousands of different kinds of caterpillars, some of them unique to certain climates and geographic areas, and some ubiquitous across entire continents. Some of them only eat particular plants (like the endangered Monarch butterfly who likes to eat milkweed). But how to tell which one is which? The best thing to do is to purchase a guide with color photographs to help you recognize what kinds of caterpillars you have in your garden. One excellent book is Peterson First Guide to Caterpillars of North America. You could also try Caterpillars in the Field and Garden: A Field Guide to the Butterfly Caterpillars of North America. These guides can help you to familiarize yourself with the different caterpillars common to your region, or the ones most likely to eat your various garden plants. For example, hornworms tend to eat nightshade plants like tomatoes, peppers and potatoes.
2 Ways to Get Rid of Caterpillars
Of course there are many chemical preparations that kill garden pests, but most vegetable gardeners are in agreement that using such products around edible produce is not a good idea. Luckily there are some non-chemical and non-toxic ways to control caterpillars.
Remove By Hand
Removal by hand is really the most effective and simplest way to get rid of caterpillars quickly. Put on some well-fitting gloves, and drop the caterpillars into a bucket of soapy water. You can also try relocating them, as caterpillars don't like to travel very far from their birthplace in search of food. Put them in a cardboard box and bring them to a meadow or roadside area with plants; obviously don't put them in someone else's garden! You might find your children are very helpful with this task, since many kids enjoy yucky bugs! Perhaps you can create a small butterfly garden where the caterpillars will be encouraged to return.
Use a Spray
One substance used to control caterpillars is Bacillus thuringiensis (Bt); this is a bacteria that is added to a spray formula. It is toxic to some insects but not to birds, fish or mammals. If you want to go this route, be sure to do a bit of research to determine that the product you choose is not harmful to bees.
Signs of Caterpillar Activity
Perhaps there is no more disheartening sight in the vegetable garden than seeing your burgeoning plants full of holes, or the leaves chewed down to their stems. Caterpillars can do a lot of damage in a very short time. They tend to be most active in late summer and early autumn, right when many garden crops are starting to get bigger. While some caterpillars are showy or distinctive and easy to recognize, others have very effective camouflage and are difficult to spot. But there are signs of their presence.
- Eggs: These are left behind on the host plant by the butterfly. They may be hard to differentiate from other insect eggs, so be observant when you see butterflies lingering on your plants.
- Leaf damage: Caterpillars usually chew on leaves from the outer edges in, as opposed to leaving holes in the middle of leaves.
- Frass: Frass is the technical term for caterpillar poop! It looks like tiny grains of black pepper, and caterpillars tend to leave it behind wherever they are actively feeding.
Causes of Caterpillar Infestation
The main reason you end up with caterpillars is because butterflies lay their eggs on or near your plants. Like many useful species in nature, butterflies have an instinctive ability to locate the safest spot that is conducive to reproduction, and in order to populate their species, they plan ahead to make sure their offspring have plenty to eat. It's as if the butterflies have determined that you're the cafeteria for their hungry youngsters. Problem is, they'll keep on eating until your own food crops are gone! Some caterpillars eat stored grains and cloth fibers, especially wool. Most caterpillars prefer one specific type of food, and may even be named after their favorite dish (such as cabbage loopers).
There are a number of effective ways to prevent caterpillars in your vegetable garden. You shouldn't need to resort to using harmful chemicals to control caterpillars; such products may harm pollinators, birds or wildlife, or leave toxic residue in your soil. Always do some research before purchasing any commercial preparation; sometimes a product will say it's "safe" on the label when in fact it's harmful in any number of ways.
Moths are attracted to light at night, so if at all possible, try not to have lights around your garden at night; this will cut way back on moth traffic. If they're not around, they won't lay eggs.
Plant Food Crops and Flowers Separately
Butterflies are most attracted to nectar-rich flowers. If caterpillars a re a problem, keeping your pollinator plantings separate from your food plantings will lessen the chance of a caterpillar infestation in your vegetable garden.
Some strong-smelling herbs will deter caterpillars, including lavender, sage, peppermint and mugwort. Don't plant mint directly in your garden, as it's very invasive, but placing a small container of it nearby may help keep caterpillars away.
As we've established, insects are smart, or, at least, they're good at surviving. If you switch out your crop varieties and locations of plantings from year to year, it makes it harder for butterflies and moths to establish themselves in your garden.
Protection of Crops
You can protect your tender young plants from caterpillars by using protective materials. Some gardeners have success with putting cardboard or tin foil around the base of plants to repel caterpillars, who find these surfaces awkward to crawl over.
You can also use porous netting to protect your plants from caterpillars, but if the eggs were laid directly on your plants this method might have limited success.
Attract Birds Who Eat Caterpillars
There are a number of common backyard birds who eat caterpillars, or feed them to their young. These include American robins, yellow warblers, Carolina wrens, chickadees, sparrows, woodpeckers, and red-eyed vireos. Chickadees in particular prefer caterpillars for feeding their chicks. Creating a hospitable environment for these birds might can help cut down on your caterpillar problem.
Spray a Caterpillar Deterrent
There's an all-natural spray solution that Australian gardeners swear by for controlling caterpillars: just dissolve one tablespoon of horticultural molasses (available at garden supply centers) and one teaspoon of dish washing liquid (or pure liquid soap) into a liter of warm water. Let it cool, then spray it regularly over the leaves, beings sure to apply to the top and bottom. Bonus: it also deters fire ants!
Caterpillars in Your Yard and Garden. University of Missouri Extension.