Aflutter for Monarchs
Jamie Hinrichs, Pacific Southwest Region
January 13th, 2025
A monarch butterfly getting nectar from a thistle on the San Bernardino National Forest, October 2015. (USDA Forest Service photo)
Monarch butterflies (Danaus plexippus) reign supreme in human enchantment — rooted in this whisp-of-a-creature’s ability to migrate great distances. For the Western population, that flight goes between the California coastline to west of the Rocky Mountains.
But this fierce flyer has declined over the years. By December 2024, the monarch butterfly found itself on the proposed list of threatened creatures, under the Endangered Species Act. Since the 1980s, the Western migratory population has plummeted by more than 95%, due in part to lost or degraded habitat. These small-winged creatures need places to feed, rest and breed.
Fortunately, the San Bernardino National Forest in Southern California shares the national love for these butterflies. Along with partners, this forest provides breeding habitat for the conservation and recovery of this species.
And a notable milestone? In 2014, they received a National Fish and Wildlife Foundation grant to improve and restore monarch habitat.
Wolly milkweed (Asclepias vestita) is an early season milkweed, native to California. It can be found growing near the Northern Boundary of the San Bernardino National Forest. (USDA Forest Service photo)
Milkweed — Toxic Treat
“We knew there was milkweed up here, based on historical occurrences and other field surveys,” said Drew Farr, restoration botanists with the San Bernardino National Forest. “But we didn't have a good grasp on where the good populations of milkweed were. So, we started mapping.”
Milkweed is a flowering plant named for the milky sap that leaks from its leaves and stems. They are the only plants where monarchs will lay eggs. While toxic to many organisms, monarch caterpillars eat the leaves with reckless (and harmless) abandon.
Globally, there are an astounding 200 species of milkweed. But some are actually dangerous for monarchs.
“In the commercial nursery trade, the most common milkweed species is a tropical species. And it can carry an organism (Ophryocystis elektroscirrha) that can kill monarchs,” said Farr. “That tropical milkweed can survive year-round in areas with a mild winter. So, it allows that organism to build up inside the sap of the milkweed. Then, when the caterpillars eat the milkweed, they get that parasite into their system, and it ends up killing them.”
This is why native, early-season milkweed are essential. Unlike the tropical species, this variety dies back seasonally, limiting that parasite from multiplying and infecting monarchs. That is why the San Bernardino National Forest has been working with partners on ways to propagate native, early season milkweed for Forest Service and public use.
Butterfly Health Checkup
Volunteers and Urban Conservation Corps members help establish an early season milkweed seed bed in Big Bear. Ascelpias californica seed collected from this bed helps restoration work on the forest. (USDA Forest Service photo)
Photo Credit: (USDA Forest Service photo)Forest staff have also been recording monarchs, noting their life stage, general health, and type of milkweed they use on national forest land. This information helps with the when and where to collect milkweed seeds.
Timing is key. Milkweed, like dandelions, have pappus — a white, fluffy structure that allows the wind to carry the seeds away from the plant. Equally essential … ensuring seed collection does not disturb any monarchs using the milkweed.
“All of our staff is familiar with the life stages of the monarchs, so we can avoid them when we're scouting for seed,” Farr explained.
Seed collection lays the groundwork for the forest to grow native milkweed, already an important part of restoration projects. Many of those projects aim to help habitats, especially in areas damaged by wildfire or recreational use.
For example, off-highway driving sometimes impacts important plant habitats. So, partners like the California Off-Highway Motor Vehicle Recreation Division and Southern California Mountains Foundation work with the Forest Service to include milkweed in planting projects. But in moderation.
Volunteers plant milkweed and other pollinators near Lake Arrowhead on the San Bernardino National Forest during National Public Lands Day 2023. (USDA Forest Service photo)
“If you have a lot of milkweed, it might attract parasitic insects. So, when we do our restoration work, we have milkweed as well as other pollinator type plants,” said Farr.
Keen to help monarchs in your own backyard? Farr recommends asking your local native plant nursery for a native milkweed that works best in your area.
“It's important to incorporate native plants like the early season milkweeds into gardens where we can. Even a small patch in your garden might be really beneficial for monarchs and other insects.”