FROM EGG TO BEETLE

of the larvae liquify and reform into a completely

different looking insect, the adult. When the adult

is fully formed, it splits open the pupal shell and

emerges, at which point its exoskeleton is still

soft and whitish colored, so it is unable to fly, a

condition referred to as “teneral.” Over a number

of hours or days, the cuticle and exoskeleton

harden, allowing the insect to begin its adult life.

This life cycle— egg, larva, pupa, adult—

contrasts with that of the older and simpler insect

orders, called hemimetabolous insects. These

include the Orthoptera (grasshoppers and

crickets), Blattodea (cockroaches and termites),

Hemiptera (true bugs), and numerous other

groups, which have a life cycle where the egg

hatches into a nymph (this looks like a smaller,

wingless version of the adult). The nymph then

grows by molting until it eventually becomes an

adult, with no pupal stage. One of the advantages

of the holometabolous system is that the larva is

totally different from the adult, so it often does not

live in the same habitat, does not eat the same

food, and is not subject to the same dangers.

This reduces competition between generations

of the same species, and uses the resources of the

environment more efficiently, and it may also be

one of the factors that has led to the success of

the “big four” insect orders.

Adult

Pupa

Egg

Larva

(mealworm)

above | The typical life cycle of a beetle, as shown for

the Yellow Mealworm Tenebrio molitor (Tenebrionidae). The

female lays an egg from which a first instar larva emerges.

After growing through several molts, the larva transforms

into a pupa. The adult male and female beetles emerge from

the relatively short pupal stage and start the cycle again.