Indicator Species: MonarchsOctober 19, 2017
The Monarch butterfly may be North America’s most prized insect. Orange wings with black veins like stained glass and white dots highlighting the edges make the Monarch strikingly beautiful and recognizable by all. I remember learning about Monarchs back in elementary school, when I first learned how caterpillars metamorphasize into butterflies. Aside from their esteemed beauty, Monarchs (Danaus plexippus) have an immense ecological value as well: they are considered indicator species.
WHAT IS AN INDICATOR SPECIES?
Indicator species are so named because their population’s presence, absence, or alteration are said to reflect changes in environmental conditions. Lichen, for example, are very sensitive to heavy metals and thus considered an indicator species for pollution and changes in air quality. Lichen often grow on the barks of trees in the forest, where air pollution is lower than in urban environments.
Monarchs are considered indicators for a number of reasons. As adult butterflies, Monarchs live only three to four weeks. Because of their short lifespan, environmental changes impact the Monarchs quickly, and changes within and between generations are more visible to ecologists. Second, the species distribution is wide: summer habitats in North America range from New England, to the Great Lakes region, north to Canada and west to the Rocky Mountains and California. In late fall, they migrate 2,000 – 3,000 miles to the Sierra Madre mountain range in Central Mexico to spend their winter months. Tens of thousands gather on single trees, making the forest glow and flutter orange.
(Photo Source: Black Point Group)
The World Wild Life Fund describes this behavior as the “most highly evolved migration pattern of any known species of butterfly or moth and perhaps any known insect.” The migration is particularly staggering because of the short life span: it will take 3-4 generations for the Monarchs to migrate from Mexico to the US and Canada. Scientists still do not understand how new generations know to continue the migration.
WHY SHOULD I CARE?
Aside from being America’s Bald Eagle of insects, Monarchs drink the nectar of a variety of wildflowers, pollinating them in the process. They are a food source for birds and larger insects, making them a vital link the food chain.
In recent years, Monarch populations have declined. The area they populate in Mexico “the butterfly hectare” reached a 20-year low in 2013, dropping from seven hectrares to three, a 43.7% decrease. In 2004, an estimated 550 million Monarch migrated to Mexico, while in 2013 just 33 million did.
WHAT CAN WE DO?
In two words: plant milkweed! Milkweed and Monarchs have co-evolved together. There are several types of milkweed species, but it is the only plant that Monarchs will lay their larvae eggs on. The larvae hatch and immediately start eating milkweed leaves. Most animals are sensitive to the toxicity in milkweed, but Monarchs can store the cardenolides in their bodies as a defense to ward off predators.
Milkweed (Asclepiadacea) is native to north America and naturally found in meadow borders along forests. Recently, milkweed populations have declined from the spread of synthetic pesticides from nearby landscapes, and the increase of glyphosate-resistant corn and soybeans on farmlands. By planting more Milkweed in our yards and communities, we can help create a corridor for migrating Monarchs. Planting Milkweed in a meadow with other wildflowers is ideal for conservation efforts, because it provides a food source as well as a habitat.
Feeling inspired? Check out how we converted a traditional monoculture lawn into a mecca of biodiversity for pollinators, including the Monarch, in our latest video: Good Witches Garden Part 6 – Finale. You can watch the journey from the beginning on our YouTube channel-- subscribe to stay updated!
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