Monarch Butterflies

Famous for its cross-continental migration, the eastern North American species of the monarch butterfly is well-known across New England for its notably bright appearance.  Often traveling in large swarms, also known as kaleidoscopes, the monarch butterfly gets attention for its distinct black and orange wings that have been noticed by Americans and people worldwide for hundreds of years.  Acting as pollinators, the butterflies also further the growth and development of many attractive flowers and other plants.

The monarch butterfly starts out its life as an egg laid amid milkweed leaves, a plant that it will feed on at different points throughout its initial development.  Within three to five days, the egg will hatch, releasing a first instar larva.  Over the next nine to 15 days the caterpillar increases its body mass by a factor of 2000, molting five times in the process.  Only five percent of caterpillars survive the past the final molt, as the majority of the infant butterflies are preyed upon by ants, spiders, beetles, lacewing larvae, and other predators.

Once the larva has completed its molting sequence, it pupates, entering into a two week period as a chrysalis.  Upon its emergence from this state, the insect resembles the traditional image of a monarch butterfly, having fully developed and become capable of flight.  The butterfly will then begin to drink nectar and mate, laying its own eggs if a female.  One of the best examples of mimicry in nature, the monarch butterfly appears virtually identical to the unpalatable viceroy butterfly, further discouraging birds and other predators from consuming the already-poisonous insect.  As a result of this defense mechanism, a non-migratory monarch can live up to two to six weeks in optimal conditions; three to four generations of monarchs can develop over the course of one summer.

Some monarchs can live much longer, however.  Migratory monarchs, which live seven to nine months, are the butterflies well known for making a pilgrimage from New England all the way to Mexico and north again every year.  The adult monarchs of a summer’s final generation, instead of laying eggs, migrate to central Mexico, where they settle on south-facing slopes of mountains and branches of oyamel fir trees to go into a torpor, similar to a mammal’s hibernation, for the winter.

Once warmer weather returns, these winter monarchs migrate again to northern Mexico and southern states like Texas to lay the first generation of eggs for the new summer season before dying.  The new eggs eventually hatch and migrate back to New England upon the appearance of milkweed in the area to continue the cycle.

Despite its historical regularity, this cycle of migration faces its own form of endangerment.  Over the last 20 years or more, harsh climates, logging in Mexico, and the use of fatal pesticides have begun to decimate the habitat of monarch butterflies both in Mexico and New England.  Most importantly, said logging and pesticide use has had a dramatic impact on the availability of milkweed throughout North America, the only plant that monarch caterpillars feed on.  As a result, the population of monarch butterflies is down to what some scientists estimate as a tenth of its previous heights.

Luckily, there are some ways that the average person in New England can help preserve this threatened species.  In July, for example, Sustainable Wellesley received 32 milkweed plants and made them available to its membership in sets of four.  All of the plants were claimed and are now planted throughout Wellesley, providing potential egg-laying sites for monarch butterflies all over town.

There are other ways one can pitch in too.  As part of the North American Monarch Conservation Plan, scientists look to monitor the location and migration of monarch populations all over the continent, a process that anyone can volunteer to help out with.  Additionally, Wellesley residents can help reduce habitat destruction by avoiding the use of herbicides and pesticides.  Sustainable Wellesley is also considering purchasing another set of 32 milkweed plants this fall; residents can email to reserve theirs.

(Matthew Hornung and Olivia Gieger)


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