They are the most loved, admired and respected of all the “creepy crawlies.” Two year olds and insect-phobics readily hold them. Nursery rhymes tell of their concern for fire and propensity to fly away home when their children are all alone. Familiar to everyone all over the world they are, of course, the ladybugs. Technically they should be called lady bird beetles. Because to an entomologist a “bug” means a specific kind of insect and “ladybugs” are actually beetles and not true bugs. But we’ll just call them ladybugs anyway.

There are over 175 species of ladybugs in California but the commonest one is the Convergent Ladybug, Hippodamia convergens. This common name refers to the two white marks on the black thorax (right behind the head) that would meet if extended. The spots vary from none to 12. Males have slightly larger feet than females and can easily climb the sides of a glass jar. Females with smaller feet cannot climb glass.

For nine months out of the year there are huge aggregations of Convergent Ladybugs gathered on fence posts, fallen trees and in shrubs in the coast ranges and the foothills of the Sierra Neveda.. These clusters tend to be in open areas of the forest where the sun shines through the trees. These ladybugs were born either in the Sacramento or the San Joaquin Valley.

In the Central Valley, an adult ladybug will lay around 1,500 eggs. These hatch in about five days into alligator-shaped larvae that are black with orange spots. These larvae are voracious eaters and feed on pollen and aphids. One teen-age ladybug may eat 400 aphids before becoming an adult. This insatiable appetite has endeared ladybugs to gardeners.

By early June, times are getting tough (hot and dry) in the valley and the adult ladybugs fly up until they reach a temperature ceiling of 55 degrees F. On some days this may be up as high as one mile. The breeze then blows them to their next promised land. The predominate northwesterly wind sends the majority into the Sierra Nevada foothills. But an east wind will propel some of them to the coast. The ladybugs that we see in our local forests may have traveled over 300 miles. Quite an accomplishment for a tiny insect.

The ladybugs stick around here for nine months and form the massive colonies that are now visible. Laboratory experiments suggest that the clustering is stimulated by reduced temperature and light. In the Sierra they have been found at 6000 feet clustering and surviving under snow drifts! The ladybugs are basically hibernating and do not eat but live off their accumulated aphid fat.

Why the colossal clusters? One suggestion is that predators (birds) are discouraged from eating ladybugs because of the obnoxious odors emitted by the large group. But another major motivating factor may be sex. In these large groups female ladybugs have a wider selection of potential mates. The best partner is the fattest one because he has been able to store the most energy during the brief feeding period in the valley. This is a good attribute to pass on to your offspring. On warm days a veritable sexual orgy takes place in the ladybug clumps. Mother Goose never mentioned this.

The female can store the sperm for months. In late winter or early spring the ladybugs wait for the right wind to take them back to the Central Valley. They use the sperm to fertilize their eggs and then they die. The cycle is complete.

The ability of ladybugs to consume aphids has created a market for them. But dealers only collect the aggregations. Some of these groups may contain 500 gallons of beetles with 80,000 beetles per gallon. That’s the good news. The bad news is that when you buy your “organic” aphid control, they immediately fly away especially if the temperature is over 65. But even if they stayed they wouldn’t eat your aphids. Remember they only cluster to mate; dinner comes later.



Posted on

August 6, 2009