dictionary says that the plural for "pupa" is either "pupae" or
"pupas." When I was a kid we were obliged to call them pupae but nowadays I
think most people call them pupas. Anyway, here we are speaking of the resting stage between the larva and adult stages of insect
species undergoing complete metamorphosis.
Pupal stages vary dramatically in appearance from insect group to insect group. For example, the pupae of many butterflies develop into beautiful chrysalises (singular chrysalis),The picture at the right shows one of the most famous chrysalises, that of the Monarch Butterfly. This picture is especially nice because you can see the Monarch's orange and black wings inside the pupa's shell.
The above, of a Black Swallowtail chrysalis also is nice for the same reason. Note the future adult's segmented abdomen and, at the lower left, the enlarging wings. You can even see veins in the future wings. This chrysalis was found stuck by the silk at the picture's lower left onto a piece of plywood leaning up against a house! If you should find such a thing, the best would be to let it stay, and watch it develop each day. You can also put a pin through the silk -- but not through the chrysalis itself -- and hang it where you can watch it more closely. Just be sure that you hang it where the sunlight and humidity are similar to where you found it, and where nearby the adult can escape to freedom when it emerges. At the right is the abandoned, split-open "skin" of the same chrysalis shown above, after the adult Black Swallowtail butterfly emerged a week later.
At the left is the chrysalis of the Gulf Fritillary butterfly. Gulf Fritillary larvae feed on Passionflower vines. The species ranges all the way from Argentina to New Jersey and Iowa in the US.
Some chrysalises are beautifully camouflaged, such as the one at the right. That's the Polydamas Swallowtail, the larvae of which eat Aristolochia vines. This species occurs in the US Gulf States, into Mexico. Polydamas larvae are mostly black, so you can see that you can't depend on the appearance of a larvae cueing you as to how the pupa may look. Notice how this chrysalis attaches itself to the plant stem. In the top,right corner of the picture you can barely see two thin silk strands connecting the chrysalis with the stem.
Some pupae develop inside cocoons, such as the one at the left, which was constructed by one of the large, showy Giant Silkworm Moths. The cocoon is held together by silk spun by the caterpillar before entering its resting pupal stage. This cocoon is suspended at the tip of a slender tree branch. The cocoon is empty, with a hole at the top, where the adult moth emerged. Notice the neat way that a leaf has been incorporated into the cocoon, the leaf's midrib clearly visible bending around the cocoon's bottom.
A bagworm cocoon is shown at the right. Sometimes you can spot a bag slowly creeping along a stem. The larva is mostly hidden inside the bag, where its soft body is protected from birds who might want to eat it. Just enough of the larva's body sticks through a hole in the top of the bag to enable the larva to move the whole bag along a stem to a new location where there's plenty of greenery to eat! Once the larva eats and matures enough, then it turns into a pupa, and while it's in the pupa stage the bag stays in one place and protects it. Then one day the bag splits and out comes the adult moth.
By the way, the bagworm cocoon in the picture was found on a twig of Loblolly Pine and if you look closely you can see that some pieces pine needles have been incorporated into the bag. If the bag had been on a Redcedar, then Redcedar scales would adorn the bag. The whitish splotches are lichens that have established themselves on the bag, and this shows that this particular bag has been in service for several months! This bag is about two inches (five cm) long.
At the left you see the nests of a Mud-dauber Wasp (family Sphecidae, subfamily Trypoxyloninae). Mud daubers construct such nests from mud. The nests are partitioned off with mud and each cell is provisioned with several paralyzed spiders implanted with the mother wasp's eggs. After the eggs hatch the larvae feed on the spiders, and mature in about three weeks. Then the larvae pupate inside the dried-mud nest and overwinter. Pupation occurs while it's still inside the cell. Sometimes overwintering mud dauber nests fall off, as the one shown at the right did, and you can see into the nest's cells. Can you see the smooth, dark-gray pupas inside the cells? The cells at the bottom, right and top, middle, are empty, for comparison.
By the way, mud daubers are very different from social wasps (hornets, yellowjackets and paper wasps) in that there is no worker caste and the queens must care for their own young. You don't need to worry much about being stung by mud daubers because the wasp queens use their sting to paralyze their prey (spiders) rather than to defend their nests. Also, the wasps in general are not aggressive and they rarely sting unless touched or caught in clothing.