Blue Ridge Naturalist: Are Monarch Butterflies on Their Way to Extinction?

© Marlene A. Condon

The abundance of rain this summer made for lovely surroundings that I’d practically forgotten were ever a possibility in central Virginia. Instead of looking parched and dry, the forests—both from a distance and up close—have been lush with growth. Herbaceous plants have also grown extremely well.

The world has looked so healthy, so capable of supporting all life. But something has been missing: Monarchs, the king of butterflies, have been nonexistent.

Not a one has visited my yard and none have been visible in Shenandoah National Park when I’ve given my monthly talks. On visits to various parts of the state, I have constantly kept my eyes open for these beautiful insects, but they have eluded me. This situation probably portends the future of the one insect that most people, including young children, can recognize.

2012 was not a good year for Monarchs, the orange-and-black butterflies that make the longest insect migration in the world. Each one weighs, on average, about half as much as a paper clip, yet it might fly as much as 2,500 miles (over 4,000 kilometers) to reach Mexico by November.

When scientists measured the overwintering acreage of these insects in Mexico in 2013 (they are unable to count individual butterflies), they found only about 2.74 acres (1.19 hectares) of land with Monarchs resting on the fir trees that shelter them from cold and wet conditions. This amounted to 59% less occupied acreage than in the previous year, which is statistically significant.

Consequently, this species of butterfly may be on its way to extinction. Indeed, there have been few reports of Monarch sightings across the Midwest and the East this year. When the population of any particular kind of critter gets quite small, that species is much more vulnerable to being wiped out should a catastrophic event occur.

According to a 2011 research paper by Sweetbriar College professor Lincoln P. Brower, et al., there are three factors implicated in the decreasing numbers of Monarchs.

(1) The downward trend began with the loss of critical overwintering habitat in Mexico due to extensive illegal logging. Fortunately, the destruction of the overwintering Oyamel Fir (Abies religiosa) forests has now come to a virtual halt.

(2) There’s been a widespread reduction of breeding habitat in the United States due to land development (6000 acres a day for 2.2 million acres a year), which means fewer milkweeds—the requisite food plant—for the Monarch caterpillar. Additionally, there’s been a loss of milkweeds as a result of the increased use of glyphosate herbicide (Round-up) to kill “weeds” growing in genetically engineered, herbicide-resistant crops.

(3) Periodic extreme weather conditions have decreased the spring breeding in Texas, which is the entry point to this country for Monarchs. Higher-than-normal temperatures decrease the lifespan of the butterflies, which reduces the number of eggs laid and thus results in fewer spring- and summer-breeding generations in the eastern United States and southern Canada.

Other scientists have pointed to the management of our roadsides as a factor in the decrease of Monarchs. Highway departments use herbicides and either excessive or untimely mowing, all of which decimate milkweeds as well as the caterpillars on them.

The obsession with manicured roadways to make them “more appealing” to travelers (as VDOT touted when they held a mowing blitz in advance of the July 4^th holiday this year) is symptomatic of a culture out of touch with the serious consequences upon the environment of its actions.

Gardeners throughout the Midwest and the East could help Monarchs, but few want to plant the easiest milkweed to grow for these insects—the Common Milkweed (Asclepias syriaca). Tall and often ungainly in stature, it’s not the lovely specimen plant that gardeners concerned with aesthetics usually choose for their flower beds.

Instead they pick the Butterfly Weed (Asclepias tuberosa), a short plant with beautifully colored blooms of orange that stand out in the garden. Encouraged by virtually everyone—including some scientists who study Monarchs—to grow this plant, gardeners do a disservice to the Monarchs forced to lay their eggs upon Butterfly Weed.

Yes, these insects are forced to lay their eggs upon this particular milkweed when there are no other species nearby that are far better suited as food for their caterpillars. Unlike most milkweed species, Butterfly Weed is latex-poor and thus an inferior food plant for the Monarch caterpillar.

Latex contains the highly poisonous cardenolides that make the Monarch unpalatable to predators. These chemicals, concentrated in the abdomen and the wings of an adult where they don’t interfere with the butterfly’s metabolism, cause a nauseating taste in the mouths of predators, such as birds.

Butterfly Weed does not produce much of the cardenolides and thus confers less protection to the Monarch in both the immature and the adult phase. The result is undoubtedly an increase in Monarchs killed by predators, which must also be a factor in the continuing decline in the population of these regal butterflies.

A gardener can confirm for himself the inferior quality of Butterfly Weed by breaking a stem of this plant. The sap, rather than looking milky, as is the case with most milkweed plants and which is what gives them their name, is not at all milky. Instead it’s clear.

I first discovered this decades ago when I noticed that the Monarch butterflies never laid eggs on my Butterfly Weed. They always chose the Common Milkweed plants. The scientist in me wondered why and when I saw the difference in the sap, I surmised it must be of inferior quality. Further research confirmed my suspicion.

They say that ignorance is bliss, but ignorance can be deadly. That’s certainly been the case for our Monarchs as few people have chosen to plant the species of milkweeds that these butterflies prefer to utilize to increase their chances of surviving long enough to reproduce. And the highway department’s management of roadside growth, done without knowledge of or concern about its disastrous ecological impacts, is another case in point.

If you care about Monarchs, please grow Common Milkweed. In addition, please speak out against the excessive use of herbicides and mowing by the highway department. And last, but not least, please contact your Federal representatives to say they should support the Conservation Reserve Program (CRP).

This program pays farmers to set aside marginal land for wildlife that is not really well suited for growing crops anyway. Unfortunately, the funds allotted for the CRP have been cut drastically, yet this is one program where our tax dollars can be spent wisely. It helps all kinds of critters that help to keep the environment functioning properly so as to support mankind.