How does Pinnacles, a place set aside as a national park, help the orchardists, vintners, and farmers of California? The answer comes from the twice-yearly migrations of the convergent ladybug beetle. One of California's most abundant ladybugs, with a voracious appetite for aphids and other insect pests, this beetle begins its life in the fields and valleys where an abundant supply of their favorite food is available.
A well-fed ladybug can release up to 400 eggs during her lifetime. In March and April, the clusters of yellow eggs hatch, and the tiny larvae gorge for three or four weeks. As they grow, the larvae shed their skins, going through four stages of shedding before entering a one-week pupal stage. The black, yellow-to-red spotted pupae attach to leaf surfaces by their tails. Five to seven days later, the pupal skins split, and the young adults emerge. The adult convergent ladybug is distinguished by a pair of converging white stripes on its black thorax. Dr. Kenneth Hagen, who has studied the convergent ladybug for a number of years, notes that "a single acre of alfalfa infested with aphids during the spring may yield more than 50,000 adult convergents by late May."
Since the food supply often has been depleted by the larvae, adults migrate to the mountains in late May to early June. Huge swarms fly into the upper canyons. Upon arrival they feed on aphids if available, but more often pollen is the main food source in the mountains. The pollen produces fat to tide the ladybugs over their nine month dormancy. Congregating by the thousands, they overwinter in tight clusters, called aggregates, under fallen leaves and ground litter near streams.
The clear, warmer days of early spring trigger the ladybugs to break up the aggregates and begin several days of mating. This is when a visitor to Pinnacles National Park is most likely to note large gatherings of ladybugs, particularly along the Bear Gulch and Old Pinnacles Trails and at the Moses Springs Picnic Area.
On a windless day when the temperatures reach at least 55 degrees F, the beetles' minimal flying temperature, they begin their return migration back to the valleys and fields. As the temperature drops late in the day, the ladybugs too drop to earth, returning to the valleys to lay their eggs and die, beginning a new cycle of life and helping the orchardists, vintners, and farmers to keep their crops pest free.
"Following the Ladybug Home," Dr. Kenneth S. Hagen, National Geographic, 1970.
National Audubon Society Field Guide to North American Insects and Spiders.