Sunday, June 12, 2011

How Many Eggs Can a Monarch Lay?

Monarch laying an egg (photo by Rick Bunting)
Back in 2007  Jim Edson, from the University of Arkansas counted and came up with 326. Of course, he says, the butterfly could have laid some eggs on her journey north from Mexico….

Last week Rick Bunting, a butterfly watcher in Upstate NY happened to have his camera handy when a female Monarch was laying eggs. Monarch eggs are tiny – about 1/8 inch long – and the butterfly glues each one individually to the underside of a milkweed leaf with a quick-drying substance she secretes along with the egg.  

It takes about a handful of days (from 3 to 5) for the egg to hatch. The tiny larva (caterpillar) eats what’s left of the egg, then begins munching milkweed leaves. As it eats, it grows. When it gets too big for its skin, the caterpillar molts and then eats its old skin. After it molts about four times, the larva is ready to turn into an adult butterfly. It stops eating and finds a protected branch where it can pupate.

The caterpillar spins a bit of silk and attaches its hind end to a branch. Then it hangs head down and turns into a jade green chrysalis. The chrysalis is hard, and protects the caterpillar-changing-into-butterfly for nearly two weeks. During that time the caterpillar dissolves and reorganizes its body into an adult butterfly.

Karen Oberhauser a professor at the University of Minnesota, answers lots of questions about the butterflies. One person asked how to increase the number of eggs and caterpillars that survive to maturity (the butterfly stage). Should she try to control predators?

Not really, said Oberhauser. The most important thing to do she said, is to create and preserve habitat – and avoid the use of pesticides that can harm them. Global warming may make this more challenging. According to the models, Oberhauser said that monarch overwintering sites are likely to become much wetter than they are now. That’s because of more frequent storms, she says. The model indicates current summer habitat will become too hot, so the Monarchs may need to move farther north for breeding.

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