Monarch butterflies have been in the news quite a bit recently, due to their rapid decline. When adult monarch butterflies migrate from their overwintering grounds in spring, the females begin a search for a suitable place to lay their eggs.
Female monarchs lay their eggs exclusively on milkweed plants , one of the critical roles it plays in monarch survival. Milkweed is essential to monarch survival at each stage of their life cycle. This photo shows newly emerged monarchs drying their wings on milkweed in Missouri. If you take a close look at milkweed pods and leaves in your garden, you may find monarch eggs. And if you find one, there are likely more.
Female monarchs lay between and eggs throughout their lifetime. It takes about four days for an egg to hatch. The monarch hatchling will eat its eggshell, which is filled with nutrients, and then the milkweed leaf. A monarch caterpillar hatchling and egg. Once the caterpillar hatches, it grows rapidly. Monarch caterpillars shed their exoskeleton or molt as they grow. The black thing that pops off at the end of the video is the head capsule.
The metamorphosis of any insect that will eventually wrap himself in a cocoon proceeds in the same order. The stages are egg, larva, pupa and imago. Once the egg is hatched, the larva of the insect feeds and grows until he enters a pupa stage.
This is the stage where a monarch butterfly caterpillar, for instance, will spin a cocoon, molt to a chrysalis and enclose himself. He will emerge again as a monarch butterfly, the adult stage known as imago.
The pupa period of insects that spin cocoons is a time of great change and great vulnerability. The time that this stage takes is determined by the type of insect inside.
In some insects, the pupation period is very short. As children, many of us learn about the wondrous process by which a caterpillar morphs into a butterfly. The story usually begins with a very hungry caterpillar hatching from an egg. The caterpillar, or what is more scientifically termed a larva, stuffs itself with leaves, growing plumper and longer through a series of molts in which it sheds its skin.
One day, the caterpillar stops eating, hangs upside down from a twig or leaf and spins itself a silky cocoon or molts into a shiny chrysalis. Within its protective casing, the caterpillar radically transforms its body, eventually emerging as a butterfly or moth. But what does that radical transformation entail? How does a caterpillar rearrange itself into a butterfly? What happens inside a chrysalis or cocoon? First, the caterpillar digests itself, releasing enzymes to dissolve all of its tissues.
Many caterpillars not only change appearance as they grow and change skins but may even show different colour forms at the same stage of development within the same brood. The Silver-studded Blue Plebejus argus butterfly above left and Large Yellow Underwing Noctua pronuba moth above right are just two of the many species of lepidoptera that have broods of caterpillars containing different colour forms, both these species having green and brown caterpillars of the same age.
It seems likely this is to limit predation with one colour less easily seen than the other. The only time most caterpillars stop eating is prior to changing their skin or during the time leading up to pupation when their bodies have already begun the remarkable metamorphosis from caterpillar to moth or butterfly. However, there are also caterpillars that over-winter, including several species of butterfly, that are able to go months without feeding. The time it takes for a caterpillar to pupate varies widely according to species.
Many caterpillars are fully grown and ready to pupate within a few weeks of hatching from an egg, such as the Painted Lady Vanessa cardui butterfly above left that only takes 4 weeks. Others will over-winter in readiness to complete their growth and pupate the following spring such as the Fox Moth Macrothylacia rubi above right which remains a caterpillar for 11 months of the year from June to April. However, some species such as the caterpillars of the Goat Moth Cossus cossus may remain in the larval stage, inside a tree trunk, for up to five years.
Pupation refers to the stage when a caterpillar stops growing and undergoes a rapid and remarkable physical transformation into a moth or butterfly. The caterpillars of some moth species spin an additional outer protective case known as a cocoon around them before forming a pupa inside.
These cocoons are often spun using a mesh of spun silk and hairs from its own body. Many of these spun cocoons are rather flimsy and do not appear to offer much additional protection but their hairs may still prevent some parasites from reaching and penetrating the pupa and laying their eggs inside.
However, some cocoons are of such a solid impenetrable construction that it has been suggested that some species may have developed a body acid to burn their way out.
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