If you were to cut open a cocoon or chrysalis at just the right time, caterpillar soup would ooze out. But the contents of the pupa are not entirely an amorphous mess. Certain highly organized groups of cells known as imaginal discs survive the digestive process. Before hatching, when a caterpillar is still developing inside its egg, it grows an imaginal disc for each of the adult body parts it will need as a mature butterfly or moth—discs for its eyes, for its wings, its legs and so on.
In some species, these imaginal discs remain dormant throughout the caterpillar's life; in other species, the discs begin to take the shape of adult body parts even before the caterpillar forms a chrysalis or cocoon. Some caterpillars walk around with tiny rudimentary wings tucked inside their bodies, though you would never know it by looking at them. Once a caterpillar has disintegrated all of its tissues except for the imaginal discs, those discs use the protein-rich soup all around them to fuel the rapid cell division required to form the wings, antennae, legs, eyes, genitals and all the other features of an adult butterfly or moth.
The imaginal disc for a fruit fly's wing, for example, might begin with only 50 cells and increase to more than 50, cells by the end of metamorphosis. Depending on the species, certain caterpillar muscles and sections of the nervous system are largely preserved in the adult butterfly.
One study even suggests that moths remember what they learned in later stages of their lives as caterpillars. Getting a look at this metamorphosis as it happens is difficult; disturbing a caterpillar inside its cocoon or chrysalis risks botching the transformation.
But Michael Cook, who maintains a fantastic website about silkworms , has some incredible photos of a Tussah silkmoth Antheraea penyi that failed to spin a cocoon. If you are using a potted plant for food then you can put sticks in the dirt of the pot.
If you are using a plastic container with water for the food plant then you can just put a pot of dirt with sticks stuck in it right next to the plastic container and then aim some of the sticks into the food plant. Wherever they do pupate, they need to have space to hang their wings when they emerge from the chrysalis. We have had some pupate on a stem with a lot of surrounding leaves. To help them out we have removed the leaves so they have plenty of room to hang and expand their wings. If your caterpillars are enclosed, you will need to clean this out periodically.
If the caterpillars are in the open you may want to consider putting something down to catch the frass. We have used several different set ups. We have also used foil, an old cookie sheet that was no longer good for baking, a large open plastic container like what greens come in from grocery stores or Costco, or a plastic tray that goes under potted plants.
This is a greenish liquid so depending on what surface is near your caterpillars you may want to put some paper towels or newspaper around the area. You may want to put a paper towel or newspaper under your chrysalis or freshly emerged butterfly. It can be too hot for the caterpillars and chrysalises can dry up. That being said, we have raised caterpillars in front of a sunny window with the shade partially open. I can imagine that an enclosed caterpillar house in the sunshine would get way to hot.
So, to be on the safe side you should keep your caterpillars out of the direct sun. I hope this article gives you some ideas about making your own indoor caterpillar home. We started out with just a couple Black Swallowtail caterpillars on some parsley stuck down in a plastic container of water with some holes in the top to stick the stems through. We set this in a large plastic tray on our coffee table.
We watched it very close since we were new to this and when the caterpillars got bigger we put them in a large glass jar with holes in the metal lid. We put a couple sticks and some parsley not in water inside. We added more parsley as needed and in the next day or two we had a chrysalis on a stick. I think we left ours in the jar but at this point I would recommend carefully removing the stick with the chrysalis and putting it in a little pot of dirt to hold it upright put it at about the same angle as it was in the jar.
But at its core is a prosaic and very basic biological urge: the need to eat and grow in safety, then — and only then — to disperse. The caterpillar is a veritable eating machine — a cylindrical, plant-digesting bag. During the few days or weeks that it is active, it will devour many times its own weight in whatever its chosen foodplant might be. As in all insects, it is the larval stage that does almost all of the eating, and certainly all of the growing.
The caterpillar does this quietly and secretively. How to identify common caterpillars. In our anthropocentric world, we might expect growth and development to be uniformly incremental — from small but fully formed baby to similar but much larger adult. Some insects do grow this way — earwigs, plant bugs, cicadas, termites, grasshoppers and cockroaches. Hatchlings resemble miniature adults, with wing-buds gradually increasing until the fully winged adult size is achieved. This is called hemimetaboly, a seemingly half or partial change.
Holometaboly, a full change, is the complete — and often dramatic — metamorphosis from worm-like larvae to large-winged adults in entomological jargon, imagos or imagines.
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