Beetles are holometabolous insects, which means they have a distinct egg, larval, pupal and adult stages with each stage being radically different from the other. The evolution of holometaboly has allowed immature and adult stages to specialise in and therefore use different habitats or resources.
Beetle eggs are generally small and are laid singly or in batches. The number of eggs an individual female lays varies greatly depending on the beetle species and can be as little as a dozen, up to a few thousand.
Eggs hatch to become larvae and an individual larva can molt several times, increasing in size each time but retaining the same body shape and form. These larval growth phases are termed instars – 1st instar, 2nd instar etc. The total number of instars varies between species and is genetically determined but the rate of growth depends on environmental factors such as availability of food and temperature.
Pupation is usually triggered by attaining a critical minimum weight or body size. During the pupal stage, the organs undergo complete re-organisation.
Adult life begins on emergence or eclosion from the pupal case. A newly emerged adult is pale in colour until the “skin” hardens and darkens a process known scleratisation. This process can take several days and the beetle is at great risk of predation during this time. Beetles do not molt again once the adult stage is reached.