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Conrad Bérubé |
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Conrad Bérubé |
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The following is an excerpt from a handout prepared for
Entomology 111: Insects and Human Affairs at the
University of California/Davis.
I've never really understood that bit of folk doggerel that most of us learn as kids: "Ladybug, ladybug fly away home, your house is on fire, your children are burning." For one thing it doesn't even rhyme; secondly, whoever heard of a ladybug house? As near as I can figure, the little ditty probably springs from the practice (still in use in many parts of the world) of setting agricultural fields afire to clear stubble and release nutrients bound in plant debris back into the soil (much the same function that termites serve in natural ecosystems)-- when the fields were aflame the ladybugs' "homes" would be on fire, their offspring, lacking wings, like all immature insects, would not be able to escape the blaze and would perish.Ladybugs, or more correctly lady beetles (order: Coleoptera , family: Coccinellidae), have long been valued because they eat many common homopteran pests of garden and farm (like aphids and whiteflies). In fact, their name (originally "Our Lady's beetle") refers to the fact that they were once considered to have been sent in answer to prayers to the Virgin Mary to save crops from insect pests. One type of lady beetle, Rodalia cardinalis , was imported to California late in the last century and is credited with saving the growing citrus industry from the devastation caused by the cottony cushion scale, Icerya purchasii (which, itself, had been imported inadvertently).
The convergent lady beetle (so called because of the white lines on its prothorax that converge towards its head) is native to California and its life history illustrates several of the concepts we've read about. They practice both a strategy of migration ("escape in space") and diapause ("escape in time") to avoid harsh environmental conditions. In the central valleys, a new generation of beetles is produced in the spring, where the larva, which look something like little six-legged alligators with their jaws on sideways, gorge themselves on aphids and similar insects. During the hot summer, when little prey is available in the valleys, the adult beetles migrate to the sierra where they may continue to find food until the fall. As the days shorten, they enter into a state of "suspended animation", or diapause, in large clusters sheltered under logs or other debris which serves to insulate them from the extreme cold. In the spring, the beetles mate and migrate back into the valleys to exploit the new crop of aphids attacking the plants there. The lady beetles' red pigmentation acts as warning coloration (or aposematism) and alerts animals that might eat them that they taste bad (due to the presence of the chemical precoccinelline).
Mashed lady beetles were once prescribed as remedies for such diverse illnesses as colic, measles and toothache. Such remedies should not be scoffed at automatically since many insects produce chemicals that have legitimate uses as drugs. Ants were once the principal source of formic (from the latin word for "ant") acid. The compound known as "spanish fly" (which effects priapism, i.e. prolonged erection of the penis in male mammals) is produced by blister beetles and was used by the ancient Romans to improve performance at orgies and has also been fed to stud livestock to stimulate breeding-- but it is toxic at high doses, causing painful blisters and sometimes death.
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