The common milkweed (Asclepias syriaca) found growing in abandoned farm fields and along roadside edges is quickly dismissed as a “weed”. The milkweed is so much more than an unwanted plant growing in unwanted places. This underrated native herbaceous perennial produces beautiful sweet smelling flowers that makes it a pollinator favorite and it is also the host plant of the Monarch butterfly caterpillar. The common milkweed represents one of over a 100 species that grow naturally in North America. The plant is easily recognizable by it long oval leaves that grow opposite one another on a single main stem that when broken “bleeds” a white milky substance. The old adage “you are what you eat” rings true for the monarch butterflies that take on the bitterness of the leaves making it a revolting meal to birds and other potential predators. The brilliant orange and black coloration is a reminder warning birds to stay away!
Milkweed flowers bloom from late June throughout July in the Northeast. The flowers themselves form a perfectly symmetrical ball of 40 to 50 individual white to pinkish blossoms filled with nectar to lure in a diversity of pollinators. The nectar reward is a gift to all who dare attempt to stay on the slippery flower, it is common for an insects legs to slip into anther pouches. By design the insect becomes trapped and must exert force to pull its legs free along with the attached pollen (paired pollinia). Visiting other flowers a similar process occurs and pollen is exchanged, achieving cross pollination and fertile seeds. Smaller insects, including honey bees often become fatally ensnared and are unable to free themselves from the anther pouches. It is common to see dead bees hanging from the flowers.
It stands to reason that the strong and powerful bumble bees are ideally suited to pollinate the milkweed. A variety of species seek out the ample offering of sweet nectar located within five nectar cups; hood like forms that face the center of each individual flower. The milkweed is a perfect plant to test your bumble bee identification skills, I personally have found five species frequenting the flowers including the common eastern bumble bee (Bombus impatiens), the confusing bumble bee (Bombus perplexus) the brown belted bumble bee (Bombus griseocollis), the half black bumble bee (Bombus vagans) and the two spotted bumble bee (Bombus bimaculatus)
The Monarch butterfly (Danaus plexippus) is known for its epic 2,000 to 3,000 mile southbound migration to its wintering grounds in the oyamel fir forest 10,000 feet up the side of the mountains in Mexico. Millions upon millions of butterflies reach Mexico around the Day of the Dead, November 1st, and are believed to be the souls of loved ones returning home. The butterflies cluster together overwintering in this microclimate that is neither to warm nor to cold but just right for the Monarchs survival. The celebrated southern journey contrasts to the northern migration that occurs in successive waves, generation by generation. Milkweed is the celebrated host plant of the Monarch butterfly and its emergence and growth aids in the generational migration north. In late March and April, the overwintering butterflies fly north only as far as necessary in southern United States, to find emerging milkweed where each female lays up to 700 eggs, one egg at a time on individual milkweed plants. The first generation of yellow, white and black stripped caterpillars hatch and quickly grow through it’s life stages, metamorphosis into adult butterflies and advance northward to lay the eggs of the second generation on emerging milkweed. The second generation continues north to lay the eggs of the third generation. The fourth generation feeds on the milkweeds in the most northern part of its range in Canada. Some of the third and all of the fourth generation migrate back to Mexico to the same trees, in the same forest on the same mountain where their great great grandparents had spent the previous winter.
The milkweed is also the host plant to the milkweed tussock moth (Euchaetes egle). These whimsical caterpillars come complete with wild bristles of orange, black and white. In the cocoon the caterpillar trades in its eccentric colorful wardrobe to become a drab and unremarkable moth. The caterpillars live and eat in small aggregations that quickly defoliate the plant that they feast on. Monarch caterpillars prefer to eat the tender new leaves while the tussock moth eats the older leaves allowing both caterpillars to coexist in harmony. As with most insects that dine on the milkweed they absorb a toxin known as cardiac glycosides that they store within their bodies. This makes them not only taste bad but can sicken animals that eat them. The adult tussock moth flies at night, and has evolved an organ that emits an ultrasonic signal easily detected by bats. One taste of this noxious insect quickly educates bats that the ultrasonic signal is not a dinner bell but a warning to stay away.
All butterflies have their preferred host plants needed for their caterpillars to complete their life cycle but as adults they are attracted to any flower with lots of nectar. The milkweed is certainly a butterfly favorite attracting countless species. The painted lady (Vanessa virginiensis) whose caterpillars host plants include everything from thistles and sunflower to stinging nettle and mint is a frequent visitor of milkweed. It is easy to spot the great spangled fritillary (Speyeria cybele) whose caterpillars can be found on violets fluttering among the milkweed flowers. A variety of skippers such as the silver spotted skipper (Epargyreus clarus) whose caterpillars host plants include locust, trefoil and bean can be found taking their time sipping the milkweeds rich nectar reserves. All these butterflies can be effective pollinators of the milkweed lured in transport the pollinia from one plant to the next.
This blog will continue to unravel the organisms that take advantage of the native milkweed plant. Stay tuned…