AMONG INSECTS WITH COMPLETE METAMORPHOSIS...
Immature insects come in a rainbow of sizes, shapes, colors and configurations -- many of them nothing like caterpillars.
DISTINGUISHING BETWEEN LARVAE, NYMPHS & PUPAE
Larvae usually look very different from the adults of their species and show no visible signs of wings. Nymphs usually look like small editions of their adults except that they bear no wings. However, they do usually bear small pads (the beginnings of wings) growing from their thoraxes after their first or second molt. Both larvae and nymphs have legs and mouthparts, but pupae, being a resting stage, have none of either.
For example, what do you see at the left? It looks likes someone has spit on a leaf, doesn't it? Well, if you get up the nerve to wipe away some of the spit you'll find a pale little immature-insect-stage called a nymph quietly feeding on the leaf, constantly producing around it the spume you see. The spume hides the nymph from predators. The spume-making nymphs of this particular kind of insect are also known as spittlebugs, and often they are abundant in weedy places. If you keep your eyes open you'll eventually see some.
Spittlebugs metamorphose into cute little adult insects called froghoppers -- because they are hopping insects, and have broad heads like frogs. Their scientific name is Philaenus spumarius and they belong to the family Cercopidae, in the Homoptera.
Sometimes you don't see the larval stage but you see where the larva has been. For instance, the picture at the left shows where a leaf miner has tunneled through the blade of a Roughleaf Dogwood, Cornus drummondii, right outside my door. The tunnel was made by the wormlike larva of a kind of leaf beetle (Coleoptera, family Chrysomelidae). The mother leaf beetle inserted an egg inside the leaf, near the margin, the egg hatched and then the larva began tunneling inside the leaf.
You can see that as the larva tunneled and ate, it grew, as might be expected. Finally you can barely see where the larva metamorphosed and exited the leaf, leaving a tiny hole. Leaf miner squiggles occur in many kinds of leaves and usually a species of leaf miner patronizes a certain species of plant leaf. Such squiggles are extremely common, so finding some leaf miner tunnels could be the goal of an interesting fieldtrip.
At the left you see a paper wasp nest. I was cutting giant bamboo for building a trellis IN my garden and inside a bamboo stem I found this nest. The neat thing about it is that on the nest's left side you can see the heads and plump, white bodies of wasp larvae. On the sides of some of the open cells on the right, you can see tiny wasp eggs. A few of the cells are capped with chewed wood-pulp. Usually when you find such a nest the cells are all capped, or else they are empty because the larvae have metamorphosed and the wasps have flown away. Maybe this nest had its cells open because it was inside a bamboo stem. There must have been a hole in the stem the mother wasp entered. Anyway, this is just another example of something you can see in everyday life if you keep your eyes open!