Save the milkweed, save the monarch

Apr 02, 2013 by Matt Terry
Expanding housing developments and dwindling field habitats have led to a decline in milkweed, a key food source for monarch butterflies. But planting some in your garden may help the iconic insect thrive, says University entomologist Marvin Gunderman. Credit: Julia Thomson

(Phys.org) —Could there soon be a summer without the iconic monarch butterfly?

That's the question raised by the most recent monarch survey, which shows a dramatic decline in both the numbers of the butterfly and the size of the area they colonize in Mexico.

Each summer the monarch embarks on a 4,000-kilometre migration from Canada and the U.S. to a small area northwest of .

Logging in Oyamel's fir forests was once considered the main culprit behind the decline in butterfly numbers, but McMaster's resident insect expert points to a new threat.

"They're vulnerable due to their food source, milkweed," says entemologist Marvin Gunderman. "It's their number one food source, but in a lot of places it's still on the books as a noxious weed. People spray it and rip it out, but it's a vital for the monarch."

Gunderman also points to the loss of butterfly habitat along the eastern seaboard as one more reason for the monarch's steady decline.

" are expanding, field habitat is being mowed over for more subdivisions, and what's in the open fields? Milkweed."

Gunderman says that a significant decline in monarch numbers probably wouldn't have much of an effect on the food chain, due to the butterfly's bad taste and toxicity.

"But it's an iconic butterfly, and we've all grown up watching it and wondering how something so delicate can make such a long and difficult migration," he says. "It's very symbolic for us."

He says the issues the monarchs face are similar to those of other insects, including bees, which sometimes receive more attention because of their direct impact on .

"The simplest approach to turning these declines around is to encourage people to cultivate wild gardens and to plant ," says Gunderman. "Otherwise the monarch could become a rarer sight."

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paul_cherubini_3
not rated yet Apr 02, 2013
I'm an entomologist and from an academic honesty and integrity perspective I think is important to point out that if someone had started  a "plant milkweed save the monarch" campaign 30 years ago it wouldn't have done anything to prevent the big monarch population declines we have seen since then. Why? it's a basic math issue - only around 1 in 10,000 home gardeners are interested in planting milkweed and so that infinitesimally small amount of extra milkweed cannot offset more than a infinitesimally small amount of the milkweed that is lost each year on a landscape scale due to sprawl and more intensive weed control practices on farms and along roadsides.