A young beetle is very different in appearance from the adults of the species because of the various stages it goes through in its life cycle. Beetles belong to the class of insects known as the Endopterygota, which means that the wings grow and develop inside the body as the beetle grows. There are four stages to the life cycle, just as in other insects – egg, grub, pupa and adult.
Beetle eggs are various sizes (from one-tenth of an inch to one inch) and almost always white in color. When the young emerge from the egg, they do have three pairs of legs and well-developed heads. This is the grub stage of the life cycle and as it grows it sheds its skin several times.
After the grub stage in the life cycle of the beetle, the insects go through the pupa stage. This is the resting stage in which it changes form. At the end of this stage, the insect has wings and elytra turned inside out because of the blood pressure of its body. As the blood recedes from these features, the wings start to form in a normal manner.
In some species of beetles it is very easy to tell the adult males and females apart because they look so different from each other. There may also be far more females than males as is the case in the bark beetles.
Most beetles reproduce sexually, but some beetle species, such as the weevil, lay unfertilized eggs and do not mate. When mating does take place, the male deposits sperm inside the body of the female to fertilize all the eggs she will produce during her lifetime. The female stores the sperm and fertilizes the eggs she produces just before they are laid.
One can hardly tell that a grub is actually going to grow into a beetle from its appearance. Not only does it look completely different from an adult, but it has different habits as well. Some grubs feed on the roots of plants while the adults feed on the leaves and the fruit.
Beetles live long lives in all the stages of their life cycle. The adults of some of the smaller species live for only a few days – just long enough to lay the eggs. The adults of larger species have been known to live for as long as 9 years under laboratory conditions.