EGG --> NYMPH --> ADULT
At the right you see a small patch of a doomed leaf of a collard plant in my garden, suffering from a heavy infestation of Harlequin Bugs, Murgantia histrionica, a kind of stinkbug found in the US Southeast. The two tiny specimens in the picture's top, right quarter are very young Harlequin Bugs recently hatched from their eggs. (You can see Harlequin Bug eggs, looking like tiny white barrels with black rings, on our egg page.)
That's also an immature Harlequin Bug at the upper left in the picture, though it's obviously of a much larger size than the small things. It's beginning to look like an adult, which is what the large bug at the lower right is, but it's not quite there yet.
That yellow thing also is a Harlequin Bug... So, what's going on here?
INSECT ORDERS UNDERGOING
Psocoptera (booklice & barklice)
Mallophaga (chewing lice)
Anoplura (sucking lice)
Hemiptera (true bugs)
Homoptera (cicadas, aphids, etc.)
*Thrips metamorphosis is between simple and complex
What's happening is that the three smaller bugs in the picture are nymphs, representing the middle part of the diagram of simple metamorphosis given at the top of this page. The smallest bugs have just emerged from the egg, and the larger nymph has already metamorphosed several times to get as large as it is, but it's not an adult yet. It's like a teenager, almost there.
Insect nymphs do not grow gradually because insects have exoskeletons -- skeletons outside their bodies instead of inside them. As insect nymphs grow, they burst through a series of exoskeletons, similar to the way the adult cicada broke through its "shell" on our cicada page. The various nymphal stages between egg and adult are referred to as instars The two small bugs at the top, right quarter of the above picture are first-instar Harlequin Bugs, while the bug at the top, left is one of the middle instars.
At the bottom left in the picture at the top you see something very special. I was lucky enough to capture a brand new adult Harlequin Bug just moments after metamorphosing from its last nymphal instar stage! This new adult's exoskeleton hadn't yet hardened or taken on its adult colors. After it sits drying and hardening awhile, it will assume the colors and hardness of the adult Harlequin Bug at the lower right.
Below is an ant-size first-instar grasshopper among the hairs on my arm. You can see that, like the above immature Harlequin Bugs, it has the general shape of an adult grasshopper (except for its complete lack of wings and its oversize head), but is much, much smaller. This recently hatched baby grasshopper will now eat and eat, molt and molt, and with each molt grow larger, until it's a full-sized grasshopper with wings and a head size more in line with its much larger body.
Now let's look at the wing situation with the Praying Mantis. That's an adult Arizona Mantis at the right. Notice how its wings extend nearly to the abdomen's end Below is an immature, nymphal Chinese Mantid. Note its half-formed, stubby wings, which are much too short for flying. The insect is whitish because it has recently molted. Though the mantid below was nearly as large as an adult, its undeveloped wings and white color indicate that it is a nymph.