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Rose/Swamp milkweed (Asclepias incarnata) emerging in my backyard

How Will the Early Arrival of Monarch Butterflies Impact Populations for 2017?


Last week, (April 20, 2017) a client brought in a sample to the Knox County Extension office. The sample was an unknown plant needing identification. Upon initial inspection, the plant was undoubtedly milkweed, likely common milkweed (Asclepias syriaca). However, this couldn't be. My milkweed growing in the backyard in Macomb had not yet emerged, and the sample before me stood six inches tall.

The sample bled milky white sap when cut, the leaf shape and venation was spot on, everything pointed to milkweed. Another great indicator was something not part of the plant but integrally tied to milkweeds all the same, monarch butterfly eggs.

Yes on April 20, a six-inch milkweed had four monarch eggs in Knox County Illinois. While at first, this may be a reason to rejoice, there can be negative impacts to the monarch butterfly's early arrival. First, let's examine ordinary monarch butterfly habits and how they may have arrived so early.

In a typical year, monarch butterflies overwintering in Mexico migrate into North Mexico and Southern US states like Texas and lay their eggs for the first new generation of the year. Those individuals that hatch will begin to make their way north, all the way to Southern Canada. So how did the overwintering generation make it all the way to Knox County Illinois?

According to a recent Monarch Watch blog by Chip Taylor, monarch butterflies 1) take advantage of tail and quartering winds to move northeast, 2) don't fly in heavy rain, 3) the minimum temperature for flight is near 50F. It seems easy to draw the hypothesis that our mild winter and spring temperatures, and little rainfall tied to the tail winds of several storms moving through the Southern US created an aerial monarch butterfly Autobahn.

Now to answer the question of why this early arrival of monarchs could spell problems for the species this year. As mentioned prior, the milkweed planted in my yard has yet to emerge meaning there are little to no plants for the females to lay their eggs. The sample brought into the Knox County Extension office was planted in a terrace with a southern exposure, creating a warm microclimate and hastening emergence.

Typically, a monarch caterpillar lays one egg per milkweed, as a feeding caterpillar can consume quite a bit of foliage. Finding four eggs on one small plant indicates a single female monarch butterfly likely had to 'dump' her eggs. Egg-dumping is depositing multiple eggs on one milkweed. Females often dump their eggs when there is a lack of milkweed, or the female is close to death.

Without any milkweed, there are no options for egg laying female monarch butterflies. Many monarch females may die without laying eggs for the next generation. While the lucky few find a small milkweed and lay too many eggs on a plant that cannot support numerous monarch caterpillars.

Reviewing the Journey North Monarch Butterfly Migration Maps, monarch adult butterflies have been spotted in the Central Plains states since late March. It is too soon to say what this early northward migration means for monarchs. Chip Taylor with Monarch Watch states in his recent blog this may be the first time in his career monarchs have been so far north this early in such numbers. (Thousands were found clustered in a row of pines in Oklahoma on April 4) Hopefully, there are still populations that remained in the southern states to utilize the milkweed much farther along than ours in the Midwest.

If you want to make your backyard a haven for monarch butterflies and more, contact your local Extension office or visit monarchwatch.org for more information.

(Before posting this blog, I checked again (April 24), and I do have about 2-inches of growth, of my swamp milkweed.)

 



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