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Life Cycle Terms for Lepidoptera

Adult: The fourth and final stage in the lepidopteran life cycle. Formed in the pupa, the adult body emerges nearly ready for its two important functions: dispersal and reproduction. The adult form is most easily distinguished by the presence of functional wings (with very few exceptions). The adult stage is sometimes called an imago.

Caterpillar: The common name for the second stage in the lepidopteran life cycle. See the official name, larva, below.

Chrysalis: A butterfly pupa.

Cocoon: The silken enclosure in which a moth spends its pupal period. Not all moths utilize a cocoon, nor do any butterflies. Some moth species (such as the bagworms, in FamilyPsychidae) spin cocoons as larvae and go through both larval and pupal stages within the cocoons. Some moths add leaves, other plant material, or debris to the cocoon.

Diapause: An extended period in which an insect has very little metabolic activity and is thus relatively inactive. The trigger for diapause is typically some environmental condition such as day length or temperature. The immediate response of the insect is initiated by both nerves and hormones and the result is the suspension of many activities. The function of diapause is to help the insect survive through an upcoming difficult period (e.g., lack of food due to a season of cold weather). The stage of life when diapause can occur is genetically determined; depending on the species it can be as an embryo, larva, pupa, or adult. Among Lepidoptera, pupal diapause is probably the most common.

Ecdysis: The process of removing the cuticle of the previous stage and emerging as the body of the next stage. Essentially identical with molt.

Eclosion: The act of the adult’s breaking out from within the pupal cuticle; the last molt in the insect’s life cycle.

Egg: The structure composing the first part of the butterfly or moth life cycle. Technically, an egg is only the female contribution to the next generation, being a single cell with the appropriate amount of genetic material (chromosomes) and an abundance of nutritional material (largely yolk) to sustain life just after fertilization. But in common usage, “egg” also means the stage of life of a new butterfly or moth that begins with fertilization and continues until a caterpillar emerges. The confusion is a result of the fact that the external appearance of an egg changes little from the time of fertilization until just before a tiny caterpillar breaks through the surface. Of course, internal changes are many, including all of the embryonic development such as cell reproduction, blastulation, gastrulation, and organogenesis.

Holometabolous: Having a complete set of metamorphic changes during the life cycle. That is, progressing from egg/embryo to larva to pupa to adult, skipping none of these forms. Butterflies and moths are holometabolous.

Imago: The adult butterfly or moth. See adult.

Instar: An insect during a period within the larval phase of life, between two molts. For example, one could refer to a second instar caterpillar.

Larva: The second stage in the lepidopteran life cycle. The larva is a worm-shaped organism specialized for spectacular growth by means of nearly constant eating. The larva lacks two abilities that the adult will eventually have: flight and reproduction.

Metamorphosis: The series of changes that lead to the forming of an adult lepidopteran organism. All Lepidoptera undergo three distinct metamorphic transformations: from egg (embryo) to larva, from larva to pupa, and from pupa to adult. This form of metamorphosis, since it skips no stage, is called complete metamorphosis. See the FAQ on this amazing transformation.

Molt, Molting: The process of breaking out of a cuticle, either periodically during larval growth or when going to the next metamorphic stage (from larva to pupa or from pupa to adult). Molting is signaled by hormonal changes (see FAQ on this).

Pupa: The third stage in the lepidopteran life cycle. Although seemingly quiet as seen externally, the pupa is busily destroying most of its larval cells and replacing them by reproduction of relatively few cells that had no function in the larva. Thus, a nearly complete reconfiguration of the animal occurs beneath the pupal cuticle, to make the adult body.

Pheromone: A chemical released by one organism and sensed by another individual of the same species. Among Lepidoptera pheromones are often used to direct one sex to the other, to facilitate reproduction. Typically, the male follows a pheromone to the female. This communication method is especially important for night-flying moths. Each species is likely to utilize a unique (or nearly unique) chemical, thus avoiding inter-species reproductive errors.

Stadium: The period between two larval molts. (plural: stadia)