A larva is the name of the stage between hatching and adulthood in the life cycle of some invertebrates (animals without a backbone). A sexually immature organism that lives on its own, a larva seldom resembles its final adult form and usually has entirely different life habits.
A larva, like a caterpillar, is sometimes thought to be a complete, separate, sexually mature organism that has a life of its own and produces more caterpillars. On the contrary, a caterpillar is only one stage (the larval stage) between the hatched egg of a butterfly and the adult butterfly itself. This is typical of one of the major characteristics of larvae—they seldom resemble their final adult stage.
There is no better example than that of the fat, slow-moving, hairy caterpillar that spends all its time eating, and the graceful, often beautiful butterfly that flits and darts from flower to flower. Because a butterfly is an invertebrate that undergoes metamorphosis (a total change in its body shape) as part of its development, it must pass through a larval stage (caterpillar) before it can become a sexually mature butterfly. Like the butterfly, moths also live as caterpillars before they reach their adult flying stage. Among several other invertebrates that pass through larval stages are bees, wasps, and beetles (as grubs), flies (as maggots), mosquitoes (as wrigglers), and frogs and toads (as tadpoles).
All these types of larvae are eating machines, since their main goal is to grow and develop as much as possible. For example, caterpillars
have powerful jaws for chewing leaves. They also do not need to move quickly (nor can they), since they often simply attach themselves to their food source. While this makes them vulnerable to predators, they use different strategies to avoid being eaten. Some use camouflage and blend in perfectly with the leaf color of their favorite food. Others arm themselves with prickly hairs that irritate or with sharp spines. Some are poisonous or taste bad. Larvae also seldom eat the same thing or live in the same habitat that they will as an adult. This means that the immature organism does not compete with the adult organism.
At some point in its short life as a larva, the invertebrate will receive a hormonal signal that will trigger the beginning of its metamorphosis into an adult. According to the type of invertebrate, the larva will go through either complete or incomplete metamorphosis. Incomplete metamorphosis has three stages (egg, larva, adult). Complete metamorphosis has four stages (egg, larva, pupa, and adult). Insects like grasshoppers, dragonflies, and termites go through the shorter, three-stage or incomplete metamorphosis. For these insects, the larva are often called nymphs since they actually resemble miniature adults in their larval stage. The nymph or larva changes into an adult by molting or shedding its outer skin several time as its internal systems develop and enlarge.
Complete metamorphosis is much more dramatic since the adult that finally emerges is so drastically different from the organism it used to be. During complete metamorphosis, the larva goes through a resting stage called the pupa, during which all of these changes take place. At the beginning of the pupal stage, the larva attaches itself to something solid, sheds its skin, and forms a tough outer case around itself called a chrysalis. Usually this is a hard shell, but it sometimes can be a silken covering called a cocoon. The changes that go on during pupation consist mostly of breaking down cells and developing new cells. Eventually the adult insect is formed inside the pupa and it escapes from its casing by breaking it open. What emerges is the former larva now transformed into an adult.
About 90 percent of all insects undergo complete metamorphosis. Certain other invertebrates, like sponges, have larval stages as a way of dispersing their offspring. For example, after sexual fertilization (union of male and female sex cells), many sponges develop thousands of tiny, free-swimming larvae that are released to be carried away by currents and to finally settle and attach themselves to the ocean bottom.
lar·va / ˈlärvə/ • n. (pl. -vae / -vē; -ˌvī/ ) the active immature form of an insect, esp. one that differs greatly from the adult and forms the stage between egg and pupa, e.g., a caterpillar or grub. Compare with nymph (sense 2). ∎ an immature form of other animals that undergo some metamorphosis, e.g., a tadpole.DERIVATIVES: lar·val / -vəl/ adj. lar·vi·cide / -ˌsīd/ n.ORIGIN: mid 17th cent. (denoting a disembodied spirit or ghost): from Latin, literally ‘ghost, mask.’