Tuesday, November 16, 2010

More than just a "Sleeping Bag"

More than just a "sleeping bag"
Today I would like to talk about a rather interesting period in the life cycle of a butterfly, the pupal stage. A butterflies' pupa is called a Chrysalis and in this stage people generally believe (mostly from what we have read as little children, books and cartoons such as  the Very Hungry Caterpillar for example) that the caterpillar goes through a stage of stasis where it spins a "sleeping bag" of sorts for itself and hibernates until it is ready to emerge as an adult butterfly. While this is generally true, the pupa, or chrysalis, is in actual fact not just a "sleeping bag" for the insect but the actual life-form itself. While it is true that the caterpillars of many moths spin a silken casing around their pupas to protect them during incubation, this casing is known as a cocoon and must be differentiated from the actual pupa inside. The chrysalis of a butterfly is basically the one stage of the butterflies life cycle, between caterpillar and adult where it just happens to do not a lot of moving.

Some interesting facts about butterfly chrysalids

1. The chrysalis IS the butterfly and not just a protective shell within which the caterpillar rests as it transforms into a butterflyNow this is a common misconception many people make and something I always remind juniour lepidopterists. Think of the chrysalis as the insect itself. Insects grow through a series of skin-changes called molts (think snakes!). When the caterpillar has eaten enough it molts its skin as it grows into a larger one. The chrysalis is the caterpillar molting into a stasis stage before it metamorphs into a butterfly. Reminder to children, you CANNOT cut open a chrysalis to watch the butterfly growing inside, that would be like sticking a knife into the butterfly and bleeding it to death! Some caterpillars, however do spin a silken case to protect their chrysalids but this case is called a "cocoon" and must not be confused with the chrysalis itself. To clear this up I've prepared the following video.

As you can see, after the caterpillar molts into a chrysalis, before the skin of the chrysalis stiffens, it does quite a lot of moving. This is because that is in fact the insect that will eventually turn into a butterfly (if you look at it up close you can actually see the developing wing discs, eyes, palps, antenna and legs)

2. The word Chrysalis comes from the Greek χρυσός (chrysós) for goldNormally one would think that a Chrysalis, as a period of stasis in the butterfly's life-cycle, would remain hidden or camoflauged with its surroundings to prevent detection from predators. And while this is essentially true with some chrysalids (those of the swallowtail butterflies for instance that are often brown if formed in dry seasons and green in wet seasons) many butterfly chrysalids are in fact gold, or golden in colour.

Shiny little devils aren't they? But the sheen of the chrysalids fade away to nothingness once the butterfly has emerged. No one really knows why some species of butterflies employ this beautiful but potentially dangerous (to the butterfly as it will more likely be spotted by predators) method of chrysalis but I think that the light reflecting of the shiny surfaces could perhaps mimic the way light reflects off water droplets on the leaves and perhaps deter predators by blinding them as they approach the chrysalis from certain angles.

Have a pleasant november!

"You will always find the single grain of sugar in the salt-shaker that is I"

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