Ladybugs of Pinnacles National Park

Ladybugs, clustered together for warmth on early spring morning.

Photo by Gavin Emmons

Nature’s Helpers: The Ladybug Migrations at Pinnacles

How does Pinnacles, a place set aside as a national park, help the orchardists, vintners, and farmers of California? The answer lies in the twice-yearly migrations of the convergent ladybug beetle. As one of California's most abundant ladybugs, this beetle has a voracious appetite for aphids and other insect pests and begins its life in fields and valleys, where its favorite food is plentiful.

A well-fed ladybug can lay up to 400 eggs during her lifetime. In March and April, clusters of yellow eggs hatch, and the larvae feed for three to four weeks. As they grow, they shed their skins, going through four stages before entering a one-week pupal stage. The black, yellow-to-red spotted pupae attach themselves to leaves. After five to seven days, the pupal skin splits, and the young adults emerge. The adult convergent ladybug is recognized by the converging white stripes on its black thorax. According to Dr. Kenneth Hagen, a single acre of alfalfa infested with aphids in spring may yield more than 50,000 adult convergents by late May.

Migration to the Mountains

As the food supply dwindles, the adult ladybugs migrate to the mountains between late May and early June. Huge swarms fly into the upper canyons. Upon arrival, they feed on aphids when available, but pollen becomes their main food source. The pollen helps them build up fat reserves to survive their nine-month dormancy. Congregating in tight clusters, called aggregates, they overwinter under fallen leaves and ground litter near streams.

The warmer, clear days of early spring trigger the ladybugs to break up their aggregates and begin mating. Visitors to Pinnacles National Park are most likely to observe large gatherings of ladybugs along the Bear Gulch and Old Pinnacles Trails and at the Moses Springs Picnic Area during this time.

Return Migration

On windless days, when temperatures reach at least 55 degrees F, the minimum flying temperature for the beetles, they begin their migration back to the valleys and fields. As temperatures drop later in the day, the ladybugs settle back to the ground. They return to the valleys to lay their eggs, completing the cycle of life and aiding farmers, orchardists, and vintners by naturally controlling crop pests.

Sources

• "Following the Ladybug Home," Dr. Kenneth S. Hagen, National Geographic, 1970.
• National Audubon Society Field Guide to North American Insects and Spiders.