A pupa (plural: pupae) is the life stage between larva and adult in insects that undergo complete metamorphosis. During this stage, the insect’s body is almost entirely broken down and rebuilt, transforming a worm-like larva into a winged, adult form. More than 80% of insect species go through this process, including butterflies, moths, beetles, flies, ants, bees, and wasps.
What Happens Inside a Pupa
From the outside, a pupa looks still and lifeless. Inside, it’s anything but. The larval tissues are broken down through a process of cellular destruction, while new adult structures like wings, legs, compound eyes, and reproductive organs are built from clusters of cells that were dormant during the larval stage. The insect essentially dissolves most of its old body and reassembles a completely different one.
This internal overhaul follows a predictable metabolic pattern. Oxygen consumption drops sharply in the early pupal stage as old tissues are dismantled, then rises again as new adult organs take shape. The enzyme systems responsible for energy production are themselves broken apart and rebuilt during the process, creating a distinctive U-shaped curve in metabolic activity from start to finish.
The pupa does not eat or grow. Growth happens entirely during the larval stage (think: caterpillar), while the pupal stage is purely about development and reorganization. This separation of growth and development is thought to be one of the key reasons complete metamorphosis evolved in the first place, allowing insects to optimize each phase independently.
How Hormones Trigger Pupation
Two hormones control when an insect enters the pupal stage. One triggers transitions between life stages, while the other determines what kind of transition occurs. When the larva has grown enough, the transition hormone surges while levels of the second hormone drop. That specific combination signals the body to form a pupa rather than simply molting into another larval stage. If the second hormone were still high, the larva would just molt into a bigger larva instead.
Chrysalis, Cocoon, and Other Protective Forms
Not all pupae look the same, and the terminology can be confusing. The differences come down to the type of insect and the protective strategy it uses.
A chrysalis is the hardened outer shell of a butterfly pupa. When a butterfly caterpillar molts for the final time, it doesn’t produce another layer of skin. Instead, it forms a rigid case that attaches to a solid surface like a branch or leaf. The chrysalis is the pupa itself, not a separate container.
A cocoon is different. Moth caterpillars spin a silky covering around themselves using silk produced from specialized glands, then form a hard inner case within that silk wrapping. The cocoon is the silk layer plus the inner casing, acting as an extra layer of protection around the developing moth.
Beyond these well-known forms, pupae fall into a few structural categories. Some have their legs, wings, and antennae free from the body (common in beetles and wasps). Others have all their appendages glued tightly against the body (typical of butterflies and moths). A third type, found in some flies, develops inside the hardened skin of the last larval stage, which acts like a protective capsule.
How Pupae Defend Themselves
Being unable to run or fly creates an obvious vulnerability. Pupae have evolved a surprisingly wide range of defenses to compensate. The most common strategy is simply avoiding detection. Many species burrow underground to pupate, putting a physical barrier between themselves and predators like birds. Others rely on camouflage, with pupal coloring that blends seamlessly into bark, leaves, or soil.
Some pupae take disguise a step further through masquerade, shaping and coloring themselves to resemble something a predator would ignore entirely. Certain butterfly chrysalises mimic dead leaves or even bird droppings. Chemical defenses are also widespread. In species where larvae and adults contain toxic compounds, the pupal stage is typically toxic too. Some ladybird pupae, for example, have tiny secretory hairs that produce deterrent chemicals. Leaf beetles carry defensive compounds called cardenolides through every life stage, pupa included.
A few species can even move. Despite their reputation as completely immobile, some pupae produce sudden jerking motions or sounds when disturbed, startling would-be predators long enough to avoid being eaten.
How Temperature Affects Development
The pupal stage doesn’t have a fixed duration. Temperature is the biggest factor determining how long it takes. In hoverflies, pupae kept at 25°C emerged in about 8 days, while those kept at 10°C took nearly two months (about 55 days). That’s a sevenfold difference driven by temperature alone.
Faster isn’t always better, though. The highest emergence success in the same hoverfly species occurred at moderate temperatures around 17°C, where roughly 85% of pupae successfully developed into adults. At the extremes, survival dropped sharply: only about 21% survived at 10°C, and around 60% at 25°C. Pupae that developed at the moderate temperature also lived longer as adults and grew larger wings. These patterns hold across many insect species, with each having an optimal temperature window for pupal development.
Pupae in Human Industry
Silkworm pupae are the most commercially significant. After silk is harvested from cocoons, the pupae inside are a protein-rich byproduct. Dried silkworm pupae average about 57.5% protein and 24% fat, making them a dense nutritional source. They’re used in animal feed for fish, poultry, and livestock, and increasingly explored as human food in parts of Asia and beyond. The oil extracted from silkworm pupae contains high concentrations of a beneficial omega-3 fatty acid and has potential applications in food production, pharmaceuticals, and cosmetics.
Beyond silkworms, understanding pupal biology matters for pest control. Because pupae are often hidden underground or inside protective structures, they can be the hardest life stage to target with pesticides. Knowing where and when pest species pupate helps time interventions more effectively.