Wild Side: Monarchs are in trouble; give them milkweed
--Dan Wilcox, outdoor columnist
Monarchs are the iconic North American summer butterfly; beautiful insects with dark orange, black and white wings. They are the only butterfly with long-distance annual migrations. Hundreds of millions of monarchs migrate from eastern North America to high-elevation oyamel fir forests in the mountains of central Mexico to spend the winter. Monarchs from western North America migrate to a few locations in California coastal forests.
Monarch females lay a single egg on the underside of a leaf on milkweed plants. A single female can mate repeatedly and lay up to several hundred eggs. The one millimeter-sized eggs hatch in about four days. Around here, monarch larvae (caterpillars) eat common milkweed, swamp milkweed and spreading dogbane (a close relative of milkweeds). The distinctive striped white, green and black larvae shed their skin four times as they grow over 10 to 14 days. Their bright markings help warn bird predators that they contain toxic alkaloids from the milkweed plants.
The mature larvae spin a silk pad on the bottom of a milkweed leaf, shed their skin, attach themselves hanging from the silk pad, and form a well-camouflaged light green chrysalis with a hard shell. After 10 to 14 days in the pupal stage, fully-formed adult butterflies hatch out, mate, and the females begin laying eggs.
Adults in the summer generations live for only two to five weeks due to the high cost of reproduction. The last generations of monarchs migrate south in the late summer and early fall to survive the long winter. Most monarchs originate more than 1500 miles from their overwintering sites. These adults can live up to eight or nine months, returning north in March and April to reproduce.
Monarchs are in trouble. Their populations are declining markedly due to diminishing over-wintering and summer habitats. Deforestation in overwintering sites in Mexico has eliminated some sites and reduced shelter and water available at other sites.
In the United States, chemical-intensive agriculture, conversion of pasture and CRP lands to row crops, urban development and roadside mowing have greatly reduced the area of summer habitat for monarchs. They need milkweeds for the larvae to eat and wild flowering plants to provide nectar for the adults.
There are currently 30 million more acres of corn and soybeans grown in the United States than in 1996. Of this, over 24 million acres are former CRP, grassland, rangeland and wetland habitats that once supported milkweed, monarchs and other wildlife. Weeds in row crops used to be managed with crop rotations and tillage, leaving relatively small quantities of common milkweed that provided good habitat for monarch reproduction. With the adoption of herbicide-tolerant crops, widespread application of glyphosate has all but eliminated milkweeds from row crop areas.
The increase in row crop acreage in the U.S. is largely due to the ethanol mandate and subsidies passed by Congress in the 2007 Clean Energy Act. Corn acreage has increased every year since then except for a slight decline in the last two years when more soybeans were planted. About 40 percent of corn grown in the U.S. now goes to make ethanol. Farmers have been plowing up highly erodible land, removing hedgerows, narrowing field margins and planting through grassed waterways.
In addition to eliminating milkweed habitat for monarch butterflies, plowing up marginal land to grow corn and soybeans has led to massive erosion of topsoil readily apparent around here this wet spring. I consider this mining, not agriculture. It’s greedy short-sighted taking of soil fertility from future generations that is also ruining wildlife habitat and spoiling our rivers and lakes.
Monarch butterfly populations can rebound if they get some good weather during their migrations, if their over-wintering areas in Mexico are protected and if there are enough milkweeds to allow them to reproduce. We can help by protecting grassland areas with established milkweed, by limiting how much we mow, by restoring prairies and by replanting grassed waterways. We can plant milkweeds in wildflower gardens that attract monarchs and other pollinating insects. It just wouldn’t be summer without monarchs winging it across the fields.
Please send any comments and suggestions for this column to me at firstname.lastname@example.org.