CATERPILLARS AND BUTTERFLIES

The Willamette Valley grasslands and woodland margins host lovely native butterfly species, including many that are endangered. But these small and vulnerable creatures are threatened by urban development, mass agriculture and farming, herbicide use, and the spread of invasive species.

Pros and Cons: In addition to being beautiful creatures, butterflies are excellent pollinators, making them valuable players in the food web. And there are even a few native butterflies that will overwinter in urban garden settings. But city gardens also provide havens for nonnative fluttering insects such as the cabbage white butterfly (Pieris rapae), which, when still a caterpillar, is one of the most common garden pests. They adapt well to urban habitats and enjoy our penchant for growing their favorite larval foods: cruciferous vegetables such as cabbage, kale, and broccoli.

Battle Plan: Remove unwanted cabbage white caterpillars from your plants in the evening. It’s easiest to pick them off by hand. Remove the eggs too, which overwinter on cabbage, broccoli, brussels sprouts, and other crucifers, and are ivory and spindle shaped. Don’t apply Bacillus thuringiensis (Bt), though. This naturally occurring bacterium will kill desirable butterflies as readily as it will the cabbage white.

Helping Hands: The thrilling anise swallowtail (Papilio zelacaon) is the butterfly you want in a Pacific Northwest garden. Like most butterflies, it needs sunny areas for basking and a water feature or puddle in which it can drink. To attract it, plant good hosts for its larvae, like fennel, angelica, parsley, carrot, and dill. But remember that if you allow the butterfly’s eggs to hatch in your garden, you’ll have to sacrifice some plants for the larvae to feed on before they undergo metamorphosis. Adult anise swallowtails feed on the nectar of lilac, lupine, camas, columbine, fireweed, balsam root, manzanita, penstemon, and more.