Sunday, June 2, 2019

Pollinator of the Week: Monarch Butterflies by Caroline Reardon

Monarch migration, photo courtesy
In mid March, the Monarch butterflies, Danaus plexippus, who’ve overwintered in temperate central Mexico and southern California, mate and then begin their migration northward. Most fly either on a Midwest/Eastern path or along the Pacific coast, but some “strays” do fly through Colorado. 

Monarchs lay their eggs on only native milkweed plants where the larvae (caterpillars) emerge and feed on the leaves. Within a month they’ve emerged from a chrysalis as butterflies where they continue the northern migration while it’s warm. Three more generations develop and migrate; as the weather turns colder, the fifth generation, which has a much longer lifespan, makes the 2-4,000 mile trip back to its southern habitat.

Monarch on Asclepias speciosa, photo courtesy
Many circumstances affect the success of this migration. Natural causes take some Monarchs, and pesticides and insecticides kill many. Glyphosate herbicides sprayed along roadsides and in crop fields have radically reduced the number of host milkweed plants the Monarch must have to survive. And in their Mexican “home,” villagers rely on the host fir trees for their fuel, housing materials and income through logging ventures, so deforestation is reducing their habitat.  

The World Wildlife Fund reports that in 1996, hibernating Monarchs covered 45 acres of Mexican forest; in 2013 they needed only 1.6 acres! In 2015, though, their habitat grew to 10 acres, still small compared to twenty years before, but perhaps an optimistic trend. 

What can we do to help? 

  • Plant a garden of native milkweed. In our area, the Monarch lays her eggs on the showy milkweed Asclepias speciosa and the broadleaf milkweed Asclepias latifolia.  Gather these from wild areas in the fall and plant before winter or check for free seeds you can stratify in the refrigerator 1-2 months before spring planting.
  • Limit the use of pesticides and insecticides in your yard. Larvae are extremely vulnerable and the butterflies landing on sprayed plants can be poisoned.
  •  Plant a butterfly garden that will provide nectar for the pollinating Monarchs. See CSU Extension’s Attracting Butterflies to the Garden for a list of butterfly-attracting plants

For further information: