Are All Butterflies and Moths Good for Gardens?
The Verdict: Mostly busted. Adult butterflies are harmless pollinators, but many moth and butterfly larvae are serious garden pests.
Why People Believe This
Butterflies are beautiful, and we have been taught since childhood that they are good for gardens. Moths get a warmer reputation by association. The "save the butterflies" message is everywhere, and it is a worthy cause. But this blanket positive framing ignores the fact that the caterpillar stage of many species can devastate your crops.
What the Research Says
UC IPM identifies several moth and butterfly species as significant garden pests in California. Cabbage white butterflies (Pieris rapae), those charming little white butterflies fluttering over your brassicas, lay eggs that hatch into voracious green caterpillars that can strip kale, broccoli, and cabbage down to skeletons. Tomato hornworms are the larvae of the five-spotted hawk moth. Codling moth larvae are the "worms" inside your apples. Corn earworms, beet armyworms, and diamondback moths are all common in Santa Cruz County gardens.
UC Master Gardeners of Santa Cruz County note that cabbage white butterfly damage is one of the most common pest complaints from local vegetable gardeners. The adults are pollinators, yes, but each female lays 300 to 400 eggs on your brassicas over her lifetime. That is not a trade-off most gardeners are willing to accept on their dinner crops.
What to Do Instead
Use lightweight floating row covers (like Agribon AG-19) over brassicas and other susceptible crops to physically exclude egg-laying moths and butterflies while allowing light and water through. This is the single most effective and least toxic control method. For caterpillars already on your plants, hand-pick them or apply Bt (Bacillus thuringiensis var. kurstaki), a targeted biological insecticide that only affects caterpillars and is approved for organic use. Support butterfly habitat in non-crop areas of your yard with native plants like milkweed, buckwheat, and coyote brush.
This week: Inspect the undersides of your brassica leaves for tiny yellow or white eggs and remove any you find before they hatch.
For more on managing garden pests, check out our free Garden Planning Guide at Your Garden Toolkit.
