Why Are White Caterpillars So Bad For Your Garden?

If you see a dainty white butterfly with black markings fluttering around in your yard this spring and summer, you might want to head over to your garden and check on your cabbage.

Wait, my cabbage? Yes, because the tiny offspring of these butterflies are called cabbage white caterpillars. They like to feed on cabbage leaves, along with the leaves of all vegetables in the Brassicaceae (or Mustard) family, like broccoli, cauliflower, kale and Brussels sprouts. (If only we could get our kids to go so crazy over these veggies.)

Without intervention, the leaves of the veggies you painstakingly cultivated all season long will soon be riddled with pin-sized holes — tangible evidence that the caterpillars have been feasting at your garden’s expense.

What are Cabbage White Caterpillars?

Also known as imported cabbage worms, cabbage white caterpillars are an invasive species that originated in Europe, Asia and North Africa. Certified entomologist David Price, the technical director for Mosquito Joe, a national pest control company, says these white caterpillars came to the U.S. in the 19th century via trade and migration.

Surprisingly, cabbage white caterpillars are not actually white — they’re green! The name refers to their love of cabbage leaves and metamorphosis into white butterflies when they reach adulthood. Their green color, says Oregon State University horticulturist Heather Stoven, can make it hard to distinguish between cabbage whites and other caterpillars that also happen to be green (there are several).

Cabbage whites do, however, have at least one distinguishing characteristic. “They tend to be kind of velvety because they have small hairs on them,” Stoven says.

Why Do Cabbage White Caterpillars Eat Cabbage Leaves?

Just like we sometimes grab the closest snack when we’re hungry, cabbage white caterpillars like the leaves of vegetables in the Brassicaceae family because those leaves are easily accessible, Price says.

“(The butterflies) lay their eggs on the underside of the leaves … and then those eggs will hatch, and the larvae feed on the leaves of those vegetables, and that is where the damage happens,” Price says. They can do a considerable amount of harm in a short period of time; their life cycle is only 32 to 45 days.

You’ll know you have an infestation because you will see where the caterpillars have chewed through leaves, thanks to the pin-sized holes mentioned above.

How Do I Get Rid of Cabbage White Caterpillars?

Fortunately, cabbage white caterpillars are not harmful to humans, and the vegetables they chew through are safe to consume. Still, no gardener wants to stand by while a bunch of butterfly larvae wreak havoc on their prized produce beds. What can you do to stop this from happening? Here are a few ideas:

• Place butterfly-proof netting over your garden. If the edges are secure, the netting should keep the butterflies out. Install the netting in the springtime, says Price, and inspect the underside of the veggie leaves once a week. If you do see any eggs (they’re yellowish and elongated), remove them. “This will stop that lifecycle so they will never become larvae and start feeding,” Price says.

• Attract birds to your garden. House sparrows, goldfinches and skylarks will feed on the caterpillars, helping eliminate the problem. Parasitoid wasps are another option. They will attack the larvae and kill them off, leaving your broccoli leaves unscathed. (Due to their predatory nature, these wasps are used as pest control in lots of situations.)

• Spray your garden with bacillus thuringiensis (known commonly as BT). Price says it will kill the larvae without negatively affect pollinators or other creatures. It isn’t toxic to you or your family, either. According to the Environmental Protection Agency (EPA), BT poses “no significant risk to the environment or human health.”

Be aware that while these measures will help protect your garden from cabbage white caterpillars, they won’t necessarily eliminate them altogether.

“The butterflies are pretty ubiquitous,” Stoven says. “I don’t know that you are going to get rid of them … (because) butterflies have such a large range.”