Moths go through four distinct stages in their life cycle: egg, larva (caterpillar), pupa, and adult. This process is called complete metamorphosis, meaning the insect’s body is fundamentally rebuilt between its juvenile and adult forms. Depending on the species and environmental conditions, the full cycle from egg to egg-laying adult takes anywhere from a few months to over two years.
Stage 1: Egg
A female moth typically lays 40 to 70 eggs, though some species produce far more. She deposits them on or near a food source her future caterpillars will need, whether that’s a specific plant leaf, a piece of fruit, or in the case of clothes moths, animal fibers like wool. Eggs are usually tiny, disc-shaped, and difficult to spot with the naked eye.
Incubation takes roughly 4 days to 3 weeks, with warmer temperatures speeding things up considerably. Clothes moth eggs, for example, hatch in as few as 4 to 10 days during summer but take longer in cooler conditions. The embryo develops entirely inside the egg, drawing on a small yolk reserve until it’s ready to chew its way out of the shell.
Stage 2: Larva (Caterpillar)
The larval stage is all about eating and growing. From the moment a caterpillar breaks through its eggshell, it begins feeding almost nonstop. This stage generally lasts two to six weeks for many species, but it can stretch dramatically under poor conditions. Clothes moth larvae, which feed on keratin in wool and other animal fibers, can remain in the larval stage anywhere from 35 days to two and a half years depending on temperature and food quality.
Because an insect’s outer skin (its exoskeleton) doesn’t stretch, the caterpillar has to shed it periodically in a process called molting. Each phase between molts is called an instar. Most moth caterpillars pass through about five instars before they’re ready to pupate, though clothes moth larvae can molt anywhere from 5 to 45 times depending on conditions. With each molt, the caterpillar emerges slightly larger, sometimes with subtly different markings or coloring than the previous instar.
During this stage, caterpillars are at their most vulnerable to predators, parasites, and environmental stress. Heat waves early in larval development can actually alter the moth’s reproductive output later in life, pushing surviving females to lay their eggs faster once they reach adulthood.
Stage 3: Pupa
When the caterpillar reaches its final instar, it stops eating and prepares for the most dramatic transformation in its life. Many moth species spin a cocoon from silk produced by glands near the mouth, sometimes incorporating leaves, soil, or bits of debris into the structure. Silk moths in the genus Hyalophora, for instance, build multilayered cocoons with distinct inner and outer envelopes, designed to protect the developing pupa through an entire winter. Other species skip the cocoon entirely, pupating underground or in a simple silk-lined chamber.
Inside the pupal casing, the caterpillar’s body is largely broken down and rebuilt. Larval tissues that have no purpose in adulthood, like silk glands and the muscles that powered the caterpillar’s extra legs, are destroyed through programmed cell death. The cells are essentially digested from within as the body recycles their raw materials. Meanwhile, clusters of undifferentiated cells that have been dormant since the egg stage begin multiplying and specializing, forming entirely new structures: wings, antennae, compound eyes, and reproductive organs. The caterpillar’s gut lining is replaced cell by cell, with the old tissue pushed inward to form a mass that degrades while a new adult gut grows around it.
This process typically takes a couple of weeks in warm conditions. For clothes moths, pupation lasts 8 to 10 days in summer but stretches to 3 to 4 weeks in winter. Some species remain in the pupal stage for months if they enter a dormant state called diapause to survive cold weather.
How Moths Survive Winter
Not every moth completes its life cycle in a single season. Many species pause development during winter through diapause, a hormonally triggered dormancy similar in concept to hibernation. The trigger is often changing day length rather than temperature itself. When daylight drops below a critical threshold (around 13.5 hours for some species), the moth enters a holding pattern at whatever life stage it happens to be in.
Different species overwinter at different stages. Some survive as larvae, spinning silk shelters among dead leaves and resuming feeding in spring. Others overwinter as pupae inside their cocoons, which is common among the large silk moths. The box tree moth can enter diapause at multiple larval instars, giving the species flexibility to pause development whenever conditions deteriorate. Once spring photoperiods and temperatures signal favorable conditions, development resumes where it left off.
Stage 4: Adult
When the adult moth is fully formed inside the pupal case, it emerges in a process called eclosion. This usually happens at dusk. The freshly emerged moth pumps fluid into its crumpled wings to expand them and waits for them to harden before taking flight. Adults typically do not mate on the night they emerge. Roughly 70% of mating happens the following night, with any remaining unmated moths pairing up the night after that.
Female moths attract mates by releasing chemical signals called pheromones, which males can detect from remarkable distances using their large, feathery antennae. After mating, sperm takes several hours to reach the female’s storage organ and become viable, so egg-laying doesn’t begin the same night. Females generally start depositing eggs the night after their first mating.
The adult stage is by far the shortest. Most moths live only one day to three weeks as adults. Some species, like certain silk moths, don’t even have functional mouthparts and cannot eat at all. Their sole purpose as adults is reproduction. Others feed on nectar or other liquids to fuel a slightly longer reproductive window. In studies of codling moths, maximum adult lifespan topped out at about 21 days in spring and as few as 8 days during hotter summer conditions, illustrating how much temperature compresses the adult phase.
How Temperature Shapes the Timeline
Temperature is the single biggest factor controlling how fast a moth moves through its life cycle. Warmer conditions accelerate development at every stage. Clothes moths complete a full generation in four to six months in a heated building, often producing two generations per year. In unheated spaces or cooler climates, that same cycle can stretch well beyond a year.
Heat stress during development has consequences beyond simple speed. Exposure to extreme heat during the egg stage or mid-larval development causes surviving females to begin laying eggs earlier than usual once they reach adulthood, a pattern consistent with organisms rushing to reproduce when conditions are threatening. However, heat stress closer to the adult stage tends to reduce total reproductive output without changing the timing, suggesting the damage to developing reproductive tissues is harder to compensate for later in development.
Humidity also plays a role, particularly for species whose larvae feed on dry materials. Clothes moth larvae develop faster in warm, moderately humid conditions (around 60 to 80% relative humidity), which is why infestations are more common in closets and storage areas with poor ventilation.