GLEN RIDGE, NJ — In another week or so, Glen Ridge resident Nancy Nathanson anticipates seeing the monarch butterfly return to her property. Scientifically named Danaus plexippus, large-winged and patterned boldly in orange outlined in black, they will be migrating north, laying their eggs on milkweed plants, on the underside of its leaves.
At Nathanson’s home on Chestnut Hill Place, they will find three variety of milkweed growing for them. In the front yard, there is swamp milkweed. If their preference is common milkweed, that is in the backyard. Unlike the swamp variety, common milkweed sends out runners. Looking through the property fence, a lone common milkweed can be seen sprouted in a neighbor’s yard. There is also a balloon milkweed plant.
Nathanson is a member of the Monarch Teacher’s Network, on Facebook. Members of this organization teach workshops to school children about the importance of the monarch in the food chain, its migration route to and from Mexico, and the awaiting discoveries of raising them indoors once an egg is found on a milkweed leaf. Enthusiasts keep in touch through the Facebook network. Just this week, Nathanson would have told you that in Whitehouse Station, in Hunterdon County, a monarch was seen laying eggs a few days earlier. She began raising them herself in 2010.
“At that time, there was a pretty good amount of them counted in Mexico,” she said. “Since then, their numbers have gone down.”
According to Nathanson, the decrease in the population is the eradication of the milkweed by farmers who need the land for cash crops. The farmers, she said, also have the mistaken belief that the monarch, in its caterpillar stage, will eat the cash crops. But the caterpillar only eats
milkweed leaves while the adult monarch feeds only on its flowers.
The migration route of the monarch is well-documented, with Texas being its first stop heading north from Mexico. This happens at the beginning of March. And it takes successive generations for the butterfly to arrive in Glen Ridge around late May. It takes as many as five generations for the butterfly to migrate from Mexico to southern Canada.
“They breed, lay eggs, and move on,” Nathanson said. “The ones I raise are probably fourth generation. They’ve been arriving a little earlier.”
Nathanson pointed to a swamp milkweed. She said that last year, on June 11, a female monarch was right there.
“I had over 50 eggs in one day,” she said, demonstrating. “I pick the leaf with the egg on it; usually on the underside in the corner. I have a lot of leafs to check. I put the leaf on a damp paper towel in a food container.”
She brings the egg to her enclosed back porch. Three to five days later, the egg is hatched.
“A tiny, tiny caterpillar,” Nathanson said. “This is the first stage.”
Within two weeks, the caterpillar has increased in size and developed through five stages.
“By that time, I have it in a bigger enclosure,” she said. “They’re hungrier and they have more leaf. They are 2 inches long and eat two or more leafs a day.”
A caterpillar will then journey to the top of the enclosure. There it spins “a button,” according to Nathanson, and attaches itself to the button. Within a day, the insect sheds its skin and forms a chrysalis. Nathanson said when watching this, it looks as though the caterpillar is turning itself inside-out.
“It’s amazing,” she said.
But the chrysalis is a shell within which the caterpillar will evolve into a butterfly. The process takes 10 to 14 days.
“Except for the last generation that migrates, the monarch lives two weeks,” Nathanson said. “The migrating monarchs don’t lay their eggs on the way down to Mexico.”
She raised 200 monarch butterflies last year.
“That’s not as many as some in the Facebook group,” she said. “Some raised over 1,000.”
But nature can be fickle. Nathanson said in 2013 she did not get one monarch visiting her milkweed plants.
“They really like the swamp milkweed,” she said. “It’s more decorative than the common and it’s non-evasive.”
But she said a fellow-monarch raiser living in
Bloomfield warned her against growing balloon milkweed since it is not native to New Jersey.
“It’s good to have different milkweeds,” Natanson said. “I expect to have a lot of monarchs this year.”
But she also has a warning: milkweed sap is toxic because it contains glycoside.
“Always wear gloves when handling milkweed,” she said. “If you rub your eyes after handling it, the sap can put you in the hospital. It can cause corneal damage. Birds know enough not to eat the adult monarch.”