On Becoming A Butterfly
Butterflies go through several stages of metamorphosis before becoming the adult butterfly that we all know and love. Since we currently have a special nursery for monarch (Danaus plexippus) butterflies located in the back of the exhibit, I thought it would be a good time to tell you about their development. There are four main stages of complete metamorphosis that all butterflies go through: egg, larva, pupa, and adult.
Tiny eggs are laid on the underside of milkweed leaves by the females. There are several species of milkweed, Asclepias tuberosa is the one that is native to this area. They are a light white or pale green color and are approximately 1.2 by 0.9 mm in size or the size of the tip of a ballpoint pen. If you look, you’ll see them! Each female adult butterfly can lay between 290 to 1180 eggs. It will then take 2 to 10 days for the caterpillar to emerge from their egg.
Monarch caterpillars go through five growth stages called instars. After each instar, the caterpillar will shed its skin and molt into a larger larva.
- The caterpillars emerge from the tiny white egg and are a bright green color. The first instar will first consume its egg. It won’t feed on its host plant, milkweed, until later.
- The white, yellow, and black stripe pattern develops with the second instar. Small hairs or setae cover the tiny caterpillar and two pairs of black tentacles can be seen.
- In the third instar, tentacles and stripes are larger and more pronounced. During this stage the caterpillars will start to eat the edges of the milkweed leaves.
- A slightly different stripe pattern develops and white spots can be found near the back of the caterpillar.
- The caterpillar is quite large during the fifth instar and will start to eat from the middle of the milkweed leaves. Amazingly, these beauties will have grown 2000 times their original size. Now they are easy to spot! Right before pupation, the caterpillar will attach itself to the bottom of a leaf by spinning a silk pad.
The caterpillar positions itself in a “J” shape right before shedding its skin. In a manner of minutes, a fragile, green exoskeleton is left after the skin falls away and within a few hours, hardens. The chrysalis will stay like this for several weeks.
During the adult stage, the butterfly is upside down, with its head at the bottom of the chrysalis. Once it breaks through the casing, the adult butterfly will hang from the empty shell and dry its wings. During this process the butterfly must pump fluid through its wings so they can properly develop and stiffen. Then it will be ready to fly for the first time.
Most adult butterflies live 2 to 4 weeks on average. The monarch is an exception because of its unique migration. Monarchs making the journey north only live 2 to 6 weeks, But the last generation of monarchs in the migration can live up to 9 months! There are several reasons for this: the last monarch generation is not sexually mature when they emerge (as earlier summer generations are), so they are not using energy to reproduce. The butterflies in this generation go into a state of diapause where they are unable to reproduce but will become sexually mature in the spring time. The other reason the final generation of monarchs can live longer is because of the cooler temperature in the mountains of California or Mexico, which helps to slow their metabolism.