They are holometabolous insects with campaniform or eruciform larvae with well developed mandibles. The variety of forms seen in this order is truely amazing, and many weird and wonderful body appendages and protrusions have occurred. They are one of the few insects that have imagos inhabiting land, air and water. Some beetles are a pest to man, feeding on fur, wool, hides, furniture, drugs and museum speciemens. Eggs of most beetles are ovoid and usually show no interesting features or patternng.
Numbers laid by any particular species can vary from a few single eggs to many thousands.
Some cave beetles lay a single egg from which emerges a larvae which promtly pupates without feeding or ecdysis. This is an adaptation to the enviroment where the food supply can be very intermitant. Larvae have well developed head capsules with biting mouthparts, there are never legs on the abdomen, but the thorax shows the insect trait of three pairs. The Demestidae have larval forms which are covered in hairy tufts, leading to the name woolly bears, these larvae are unlike any other beetle larvae and are a pest to man in that they feed on natural fibres found in carpets. The pupae are pale in colour and protected by a thin soft cuticle.