Larva

A larva is a juvenile stage distinct from the adult form, occurring in animals that undergo indirect development—such as insects, some arachnids, amphibians, and cnidarians—before they metamorphose into their next life stage. Larvae often look very different from adults (for instance, caterpillars versus butterflies), possessing unique structures and organs absent in the adult, and their diet can also differ greatly. In smaller primitive arachnids, the larval stage is distinguished by having three pairs of legs instead of four.

Larvae are frequently adapted to environments unlike those of adults. Tadpoles, for example, live almost exclusively in water, while adult frogs can survive outside it. This separation can shelter larvae from predators and reduce competition for resources with adults. During the larval stage, animals consume food to fuel their transformation into adults. In some organisms, such as polychaetes, barnacles, and sea squirts, adults are immobile but their larvae are mobile, using this stage to disperse. These dispersive larvae are either planktotrophic (feeding) or lecithotrophic (non-feeding).

Some larvae depend on adults for food. In many eusocial Hymenoptera species, female workers feed the larvae. In the paper wasp *Ropalidia marginata*, males can also feed larvae but are much less efficient, spending more time and delivering less food. Certain organisms, like some salamanders (e.g., the axolotl), can become pubescent as larvae and never develop further into the adult form—a phenomenon called neoteny.

It is a misconception that the larval form always reflects a group’s evolutionary history. While this can be true, the larval stage often evolved secondarily, as in insects, where the larval form may differ more from the group’s common origins than the adult form does.

**Selected types of larvae**

**Insect larvae**

Only Endopterygotes among insects undergo complete metamorphosis, which includes a distinct larval stage. Based on Antonio Berlese’s 1913 classification, there are four main types of endopterygote larvae:

- **Apodous larvae** – no legs and poorly sclerotized. All Apocrita are apodous. Three forms are recognized based on sclerotization: - *Eucephalous* – with a well-sclerotized head capsule. Found in Nematocera, Buprestidae, and Cerambycidae. - *Hemicephalus* – with a reduced head capsule that can retract into the thorax. Found in Tipulidae and Brachycera. - *Acephalus* – without a head capsule. Found in Cyclorrhapha. - **Protopod larvae** – many different forms, often unlike a normal insect; hatch from eggs with very little yolk. Example: first instar larvae of parasitic Hymenoptera. - **Polypod larvae** (also called eruciform) – have abdominal prolegs in addition to thoracic legs; poorly sclerotized and relatively inactive, living close to their food. Best example: caterpillars of Lepidoptera. - **Oligopod larvae** – have well-developed head capsules and mouthparts similar to adults, but lack compound eyes; six legs, no abdominal prolegs. Two types: - *Campodeiform* – well sclerotized, dorso-ventrally flattened body; usually long-legged predators with prognathous mouthparts (lacewings, trichopterans, mayflies, some coleopterans). - *Scarabeiform* – poorly sclerotized, flat thorax and abdomen; usually short-legged, inactive burrowing forms (Scarabaeoidea and other coleopterans).