Monarch butterflies need milkweed to survive, but some plants you buy for your garden could be toxic to them.
There’s been a big drop in the monarch butterfly population. By some estimates, they’ve declined by more than 90 percent over the past 20 years.
One plant is key to the butterfly’s survival: the milkweed that’s the only thing the caterpillars can eat. Scientists say you can help monarchs by planting milkweed in your garden. But if you’re not careful, you could accidentally poison the insects you’re trying to help.
Signs of trouble
Mariana Alva-Weis is 9 years old. For the past couple summers, she’s been collecting monarch eggs and caterpillars and raising them in her backyard. She likes to watch them turn into butterflies.
“I think monarchs are very beautiful throughout their whole life and then they do that amazing thing, like some of them go across the world!" she says.
But last year, she brought a milkweed plant home for some caterpillars to eat, and all three of the caterpillars died.
“It was sad! I was crying.”
She isn’t sure why that happened. Caterpillars can die for a lot of reasons — they can get diseases and parasites. But you can also poison them without meaning to.
“It doesn’t take much: two or three bites and they’re dead,” says Chip Taylor, the director of Monarch Watch at the University of Kansas.
He says milkweed plants that are treated with insecticides called neonicitinoids can kill caterpillars. He says the insecticides are systemic — meaning they affect every part of the plant. When caterpillars eat treated leaves, the insects fall off the plant within minutes, curl up into a C shape and slowly die.
“We get emails very frequently, and we have to warn people don’t buy milkweeds from big box stores unless you’re certain that they haven’t been treated with neonics and very few of the big box stores can assure that,” says Taylor.
Some of the big box stores are slowly making changes
Starting this year, Home Depot is requiring its suppliers to label all plants treated with neonicitinoids. Last month, Lowe’s announced they will phase out products containing the insecticides by 2019.
Neither company provided anyone for an interview.
In emails, both companies said they’re working with suppliers to come up with substitutes for neonicitinoids.
Lowe's spokesman Steve Salazar wrote in the email, "We plan to have plants and nursery products tagged with information highlighting bee health and encouraging customers to be mindful of pollinator health when using pesticides. The timeframe for adding the tags is being determined."
I asked him whether his company will label plants treated with neonicitinoids. He responded, "Our focus is on making people aware of pollinator protection by including pollinator protection information on all the plants we sell."
Walmart also declined our interview request.
So how can you find milkweed that's not treated with neonics?
Chip Taylor says when you’re buying milkweed you should ask if the plants are treated with systemic insecticides.
“Go to a native plant nursery and quiz the manager of the nursery about the use of systemics. And if they can assure you they don’t use any systemics, then buy the plants from them.”
Bill Schneider owns Wildtype Nursery in Mason. He says they’re not an organic nursery, but they don’t use neonicitinoids. He says most of their plants are used to restore natural areas.
“We are in a sense trying to grow insect food, so we don’t want the plants we produce to be toxic to insects.”
Schneider says in Michigan, there are 11 species of native milkweeds to choose from. There’s the showy butterfly weed with its orange or yellow flowers, swamp milkweed, and common milkweed, for starters.
He says you can also go out and collect your own milkweed seeds from the wild.
“We go out seed collecting like some people go out garage sale shopping. You don’t know sometimes what you’re going to find but when you come upon it, it’s exciting.”
Schneider says it’s a good idea to do that seed collecting away from farm fields and other areas that could be sprayed with pesticides.