When a caterpillar is referred to by its scientific name, it is called a larva. Because butterfly caterpillars, along with those of moths, are part of the order Lepidoptera, it is also correct to refer to them as lepidopteran larvae in the plural form. The use of the qualifying term "lepidopteran" is arbitrary, but it may be used to distinguish the larvae of caterpillars and moths from the larvae of sawflies, which belong to the separate order Hymenoptera.
The common-usage word "caterpillar" dates back to the 16th century and is derived from the Middle English word "catirpeller," which is believed to have come from the Latin words for "cat" and "hairy."
Certain species of caterpillars have been valued through the ages as sources of silk. Many others are known for the damage they cause to crops. After leaving the larval stage and maturing into the winged insect stage, most cause no further direct harm.
Caterpillars are often thought of as "eating machines" because of the huge amounts of food, usually leaves, that they can consume. One species, the tobacco hornworm, is capable of increasing its body weight by 10,000 times in less than 20 days. Another species, the cotton bollworm, can cause enormous amounts of crop damage. Significant pest-control efforts are made to minimize the damage that can be caused by the hungry larvae. However, some species have been able to evolve and develop new defense mechanisms to counteract the effects of pesticides and biological controls.