A typical grub, preserved in formaldehyde.
The grub and pupa are two of the four phases in the life cycle of an insect that undergoes complete metamorphosis. The four phases are egg, larva (grub), pupa and adult. The most common usage of the term grub refers to the ground-dwelling larva of the june bug, but the term applies to any worm-like larva, including caterpillars and mealworms.
Egg
Most insects propagate their species through prolific reproduction. A single female june bug lays about 75 fertile eggs over the course of several weeks, and other species lay eggs by the hundreds. Eggs gestate for anywhere from two weeks to several months, and cold weather lengthens the gestation period. The small, oval eggs gradually grow more round as the larva inside develops.
Grub
The tiny, worm-like grubs emerge from the eggs and grow rapidly. A voracious appetite fuels this rapid growth, and grubs can wreak havoc on a yard or garden. A june bug larva grows to about an inch long, and feeds on the roots of grasses and other plants. Other grubs, like caterpillars, can devastate fruits and foliage. The larval stage of a june bug lasts approximately 9 months.
Pupa
Upon entering the pupal stage, a hard encasement forms around the grub's body. The pupa is mostly inactive, but may move slightly or twitch on occasion. For many caterpillars, this is the familiar cocoon seen hanging from branches, but most grubs pupate underground. The pupal stage for most insects lasts from one week to several months, but can be as long as 17 years in some species of cicada.
Adult
Towards the end of the pupal stage motion becomes more frequent, and many pupae change color. The adult insect soon emerges, looking very different from the larva. Though insects constitute a remarkably diverse family of creatures, all adult insects share three basic features: they have three-segmented bodies, six legs and hard, jointed exoskeletons. An insect in this final phase of life has but one purpose: to mate. Many insects have relatively short adult lifespans; the june bug dies about a month after emerging from the pupa.
Tags: pupal stage, four phases, grub pupa, several months