Called imaginal discs being flat and round , they are prevented from growing and developing by a constant wash of a juvenile hormone. As the larva feeds, its gut, muscles and some other internal organs grow and develop, but the imaginal discs are temporarily suppressed and remain dormant. The caterpillar behaves like a free-living, eating, growing but developmentally repressed embryo.
When it reaches a critical size, a burst of moulting hormone, ecdysone, is released. It will shed its skin several times in response to ecdysone, each time forming a new instar stage , but juvenile hormone keeps it a caterpillar, preventing onward development until, as it nears full size, concentrations of the latter hormone decline. In the fifth and final caterpillar instar, the imaginal discs have already begun to emerge from their enforced dormancy and started to grow.
Juvenile hormone now falls below a threshold and the next ecdysone surge stimulates the change into a chrysalis. The flattened imaginal discs now start to develop unhindered.
Within the chrysalis, an inching, cylindrical eating machine remakes itself into a beautiful flying creature that drinks through a straw. This strategy—known as holometaboly, or complete metamorphosis—partitions youngsters and adults into completely different worlds, so that neither competes with the other. Butterflies, ants, beetles and flies all radically remodel their bodies within a pupa as they develop from larvae to adults.
But what goes on inside a pupa? We know that a larva releases enzymes that break down many of its tissues into their constituent proteins. Some organs stay intact. Others, like muscles, break down into clumps of cells that can be re-used, like a Lego sculpture decomposing into bricks. And some cells create imaginal discs—structures that produce adult body parts. It also only provides a snapshot in time.
If you want to work out what happens as metamorphosis progresses, you need to cut open many pupae that you think are at different stages of development. But now, two teams of scientists have started to captured intimate series of images showing the same caterpillars metamorphosing inside their pupae. Both teams used a technique called micro-CT, in which X-rays capture cross-sections of an object that can be combined into a three-dimensional virtual model. By dissecting these models rather than the actual insects, the teams could see the structures of specific organs, like the guts or breathing tubes.
They could also watch the organs change over time by repeatedly scanning the same chrysalis over many days. One team analysed the caterpillar of the stunning blue morpho just before it started metamorphosis and a week into the process. Butterfly eggs are usually laid on the leaves of plants, so if you are actively searching for these very tiny eggs, you will have to take some time and examine quite a few leaves in order to find some.
When the egg finally hatches, most of you would expect for a butterfly to emerge, right? Well, not exactly. Butterfly larvae are actually what we call caterpillars. Caterpillars do not stay in this stage for very long and mostly, in this stage all they do is eat. When the egg hatches, the caterpillar will start his work and eat the leaf they were born onto. This is really important because the mother butterfly needs to lay her eggs on the type of leaf the caterpillar will eat — each caterpillar type likes only certain types of leaves.
Since they are tiny and can not travel to a new plant, the caterpillar needs to hatch on the kind of leaf it wants to eat. Caterpillars need to eat and eat so they can grow quickly. When a caterpillar is born, they are extremely small. When they start eating, they instantly start growing and expanding. From the outside of the pupa, it looks as if the caterpillar may just be resting, but the inside is where all of the action is.
Inside of the pupa, the caterpillar is rapidly changing. Now, as most people know, caterpillars are short, stubby and have no wings at all. Finally, when the caterpillar has done all of its forming and changing inside the pupa, if you are lucky, you will get to see an adult butterfly emerge. When the butterfly first emerges from the chrysalis, both of the wings are going to be soft and folded against its body.
The young called a nymph usually look like small adults but without the wings. Butterflies, moths, beetles, flies and bees have complete metamorphosis.
The young called a larva instead of a nymph is very different from the adults. It also usually eats different types of food. There are four stages in the metamorphosis of butterflies and moths: egg, larva, pupa, and adult. Eggs are laid on plants by the adult female butterfly. These plants will then become the food for the hatching caterpillars. Eggs can be laid from spring, summer or fall.
This depends on the species of butterfly. Females lay a lot of eggs at once so that at least some of them survive. The next stage is the larva. This is also called a caterpillar if the insect is a butterfly or a moth.
The job of the caterpillar is to eat and eat and eat.
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