Factors That Limit the Migration of Ladybugs

Ladybugs are well-known predatory beetles in the family Coccinellidae. Many different species exist, and ladybugs inhabit every continent except Antarctica. Since ladybugs thrive on aphids and other small insects, they tend to hibernate during cold winter months and reappear in the spring. Their life cycle leads to distinctive migratory patterns, and these year-long patterns can be affected by a number of factors, including temperature, food availability and human influence.

As with many beetles, changes in temperature impacts ladybugs. During the cold winter months, when temperatures drop below freezing, ladybugs remain inactive and hibernate, usually in wooded areas beneath leaf litter. When spring arrives and the temperature rises, the hibernating insects wake up and move from wooded areas to plains, agricultural land, gardens and other warm areas with plant growth. In California, ladybugs move from lower altitudes to higher mountains as the year warms, following predictable and heavily studied patterns. Ladybug migration is most easily observed during this time, when winter turns to spring, as hundreds of thousands of insects flock to farms and suburbs that surround wooded areas.

Ladybugs dine on aphids, scale insects, mealy bugs and mites--all common garden and agricultural pests. These pests hatch in early spring, and their numbers increase rapidly. When ladybugs migrate to an area, the availability of food determines the amount of time they remain present. Large gardens or agricultural plots provide massive numbers of aphids for the ladybugs to eat, sometimes causing hundreds of thousands of ladybugs to remain in one small plot of land. Once food runs out, ladybugs migrate to other areas with higher aphid populations.

Humans impact ladybug migration in several different ways. First, widespread use of irrigation in agricultural land can sustain aphid populations year-round. With the availability of food during fall and winter months, ladybugs change their migratory patterns accordingly, often staying in one place and neglecting to hibernate during the colder months. Second, humans use ladybugs for biological control agents and sell them commercially. Humans harvest ladybugs and sell them to farmers, gardeners and businesses as an alternative to harsh pesticides. Although using ladybugs is encouraged, collecting massive numbers of insects from their natural habitat impacts migratory patterns. Over-harvesting can cause changes in distribution, migratory patterns and alter the natural ecosystem. Finally, human use of pesticides on agricultural land kills not only the pests, but also helpful insects like the ladybug. By balancing natural biological control and the migratory patterns of the ladybugs, use of pesticides can be controlled and reduced.