Monarch caterpillar photo by Derek Ramsey and licensed under creative commons by Wikipedia.
By Ellen Gawarkiewicz –
Monarchs are one of Vermont’s most recognizable butterflies. Their distinctly patterned orange and black wings are both well known and loved; making them the state butterfly of Vermont, as well as six other states [1]. There are many commonly known facts about monarchs and their fondness for milkweed, but there are also many misconceptions.
One commonly mistaken belief is that monarch butterflies eat solely milkweed. Rather, it is the caterpillars that rely on the milkweed vegetation for food. The butterflies lay their pinhead-sized eggs underneath milkweed leaves as the foliage is the one and only plant that monarch caterpillars will eat. Meanwhile, the adult butterflies are often seen sipping on nectar from a variety of flowers.
Many people also think that if there is milkweed around, then monarchs should then be thriving. Young caterpillars actually have a relatively low survival rate when eating the milkweed, only about 3-11%. About 30% of larval losses are due to the mandibles of the caterpillar getting stuck in the sticky latex glue. Monarch researcher Stephen Malcolm wrote that a caterpillars first bite into the milkweed is “the most dangerous thing the ever do in their life”. However, some caterpillars have developed strategies to protect themselves from the latex. Some will chew through the midvein of the leaf to cut off latex flow to the area they are eating [2]. Every time you see a monarch caterpillar metamorphose, it has beaten the odds of survival.
Another misconception about milkweed is that it is only good for monarchs. In reality, there are actually dozens of other species that feed exclusively on milkweed as well, including many different types of the milkweed beetle, the cycnia moth, and the milkweed tussock moth [2]. There are also many pollinators such as bees and butterflies that use the nectar from milkweed as a food source, this in turn attracts other predators to the plant, which then attracts scavengers, making milkweed a valuable plant that contributes to diverse ecosystems.
Swamp milkweed photo by Derek Ramsey and licensed under creative commons by Wikipedia.
It is often assumed that mowing milkweed is harmful to monarchs. However, it is actually the opposite. The chemicals given off by milkweed’s toxic latex glue allow the adult butterflies to help locate the plant and then lay eggs on it. Caterpillars absorb the toxins and become poisonous themselves. When a milkweed plant is cut down, it grows back with an even higher concentration of latex glue, so naturally butterflies tend to prefer milkweed that has been regrown. Here in Burlington, a field off of the bike path, just north of North Beach, is known as monarch meadow. The field is currently being mowed and managed to encourage milkweed regrowth and help provide a breeding area for migrating monarchs.
Stop by the field during the late summer and you might be lucky enough to catch a glimpse of the migrating monarchs!
Ben Fisher is a rising UVM senior studying Environmental Science and taking part in a undergraduate field naturalist pilot program this summer.
[1] Official State Butterflies. Retrieved August 02, 2016, from http://www.statesymbolsusa.org/symbol/vermont/state-insect/monarch-butterfly
[2] Eastman, John (2003) The Book of Field and Roadside Open Country Weeds, Trees, and Wildflowers of Eastern North America, Stackpole Books.
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