California is home to a variety of butterflies (about 170 in fact!) but few are as interesting as the Pipevine Swallowtail. This beautiful black and blue butterfly can be found across the US, but the populations found here in Northern California are slightly different from those elsewhere and are even considered their own subspecies: California Pipevine Swallowtail. (Battus philenor hirsuta).
Butterfly larvae, better known as caterpillars, can be extremely picky eaters. The larvae of California Pipevine Swallowtails are especially selective with what they’ll eat, so much so that they only naturally feed off of one plant species: the California Pipevine. This plant is necessary for the larva to undergo metamorphosis and become a butterfly, and is known as their larval host plant.
The California Pipevine contains certain chemicals, called aristolochic acids, that are toxic to consume. The California Pipevine Swallowtail caterpillar can eat the toxic plant without issue, and even gets a special defense system from it! When consuming the plant the caterpillar concentrates the toxic chemicals within itself, and thus becomes toxic for birds and other predators to eat. The bright orange colors on the wings of the butterfly and the spines of the caterpillar warn predators that they shouldn’t eat them. This type of communication, called aposematism, between predator and prey is beneficial to both parties. The prey doesn’t get eaten (which is always a good thing), and the predator doesn’t consume something toxic or nasty tasting.
The California Pipevine Swallowtail isn’t in any threat of endangerment or extinction, but an issue is on the horizon. A closely related plant to California Pipevine, Elegant Dutchman’s pipe (Aristolochia elegans), is sometimes planted in yards as an ornamental due to it’s funky flowers. Adult butterflies will often confuse this plant for the native pipevine and lay their eggs on it. This is a deathtrap for the caterpillars because the Elegant Dutchman’s pipe is unpalatable to them, and they will eventually die of starvation. One way to curb this issue is to avoid planting exotic plants in the Aristolochia genus where Pipevine Swallowtails are known to occur. Another solution would be to plant more native Aristolochia plants, such as the California Pipevine, to offer them more suitable resources.