By Dr. Becker
The monarch butterfly is an herbivorous insect with a wingspan of 3.7 to 4.1 inches and a lifespan in the wild of six to eight months. A group of monarch butterflies is called a flutter.
These butterflies start out as eggs. They hatch as larvae and eat their eggshells. Then they eat the milkweed plants that they are perched on. As the larvae plump up, they become colorful caterpillars, and the next step is to create a hard protective shell around their bodies as they enter the pupa stage.
Ultimately, they emerge as beautifully colored adult butterflies. Interestingly, their unique color pattern serves as a warning to predators that they taste nasty and are, in fact, poisonous.
Only butterflies that emerge from the pupa state in late summer/early fall are born to fly and make the long migration to warmer climates for the winter. And they only make one round trip – the following year's migrators will be the great grandkids of this season's monarchs.
Incredibly, each new generation of butterflies follows the same route south their ancestors took, and sometimes they even land in the same tree. Monarchs can travel from 50 to 100 miles a day, and it can take up to two months to complete their journey to winter habitats.
North American Monarchs Are Now Considered Vulnerable to Extinction
An assessment just completed by NatureServe and The Xerces Society for Invertebrate Conservation reveals that North America's monarch butterflies are vulnerable to extinction. Their findings were published in March in a report by the US Forest Service.1
The two conservation organizations used data on population abundance, trends, and threats, and discovered that while the monarch butterfly is not endangered on a global level, the North American species is vulnerable to extinction.
Scientists separated the North American monarchs into eastern and western populations. The larger eastern population migrates to Central Mexico in the fall from as far north as Southern Canada. The smaller western population migrates primarily to coastal California when the weather turns chilly.
The eastern monarchs have experienced tremendous population declines and widespread threats in recent years and are now considered "critically imperiled," whereas the western population has been declining at a slightly slower rate and is categorized as "vulnerable to imperiled."
Threats to Monarch Populations
According to Bruce Young of NatureServe:
"Our findings show that even a widespread and common insect can face dramatic population declines in an alarmingly short period of time. The time is now to intensify continent-wide efforts to reduce the threats to this iconic species and prevent it from succumbing to the fate that has befallen far too many other species."2
The report prepared by NatureServe and the Xerces Society for the US.Forest Service details the monarch butterfly's distribution throughout North America, along with its life history, population, and potential causes of decline.3 The goal of the report is to provide information to government agencies, conservation groups, and the general public about the threats to the monarch.
According to the report, three threats appear most significant in the decline of eastern monarchs. These include loss of milkweed breeding habitat due to increased use of herbicides on genetically modified herbicide-resistant cropland and land conversion, logging at overwintering sites, and climate change and extreme weather.
Other possible threats include diseases, predators, parasites, and insecticides used in agricultural areas.
The threats to western monarch populations are less clear, but drought is likely an important factor, along with loss of milkweed, and changes in the number and quality of overwintering sites.
Why Preservation of the Monarch Butterfly Is So Important
Not only do monarchs beautify the environment, they also help flowers pollinate, keep weedy plants under control, and provide a food source for other animals. They also tell us a lot about the state of local environments.
Adult monarchs drink nectar from the blossoms of flowering plants, and then spread the pollen to the next plant and the next, helping to pollinate plant species. Much of the food we eat depends on the existence of pollinators such as butterflies.
Butterflies in the caterpillar stage eat the leaves of the plants they inhabit. Some eat flowers and seedpods as well, which may help plants shed leaves in the fall, and also keep them from growing out of control.
Butterflies provide a food source for other animals, including other insects, spiders, birds, lizards, and small mammals.
The presence or absence of butterflies is also used as a gauge of the health of an ecosystem. In their adult and larval stages, butterflies are sensitive to pesticides. Changes in climate can ultimately alter migration patterns and timing. Loss or fragmentation of habitat increases predation and affects migration. That's why scientists study butterfly behavior, population numbers, and migration patterns to determine the potential impact of environmental issues.