Human-induced climate change has been threatening the extinction of several plants and animal species. One of the biological wonders of the world — the North American Monarch butterflies and their migration — has been hit owing to skyrocketing carbon dioxide concentration in the atmosphere and soaring temperature. In the last twenty years, we have seen their population dwindling massively! Loss of habitat and food sources such as nectars and milkweed have been driving their decline and it soon, ecologists warn, this wonder of the world could become a thing of the past.
Monarch butterflies (Danus plexippus) are among the most adaptive insects in the world. For time immemorial, they have been crisscrossing North America — travelling 6000 miles a year in search of suitable conditions to feed, breed and grow — and spending their summers in the northern United States and Canada and then flying to the southern US and overwintering in central Mexico. Sensitive to changes in the weather and climate of the environment, Monarch butterflies rely on environmental hints to trigger their biological processes such as reproduction, migration and hibernation. Ideal temperature conditions, rain during winters and plenty of nectar and milkweed to feed and lay eggs on, drive their life-cycle.
For the last two decades, however, the things have been becoming unfavourable for the Monarchs. Climate change-induced due to human activities and the loss of habitat and food sources have impacted their population drastically. Summer temperatures are rising in the Midwest; milkweed is getting scarce in Texas due to drying up and the frequency of winter storms have increased in central Mexico. With the rising temperature, the summer breeding areas are moving further north. As a result, now the Monarchs have to travel a longer migration route. Milkweed, the only plant Monarch caterpillars feed on, too, has become unavailable leading to starving and dying of these butterflies. As the carbon dioxide levels soar in the atmosphere, the milkweeds release more toxins, thus making it poisonous for the butterflies. Monarchs can tolerate these toxins at low levels and have even adapted themselves to it and use it to deter predators and guard them against parasites. Further, cultivation of herbicide-resistant crops such as corns and soybeans has been eradicating the understory plants including milkweed which might compete with the crops. Drought can affect the quality of milkweeds too. The 2013 drought of Texas destroyed a good number of milkweed plants. The frequency of winter storms has increased in Mexico; 75 per cent of the monarchs were killed in a winter storm in 2002. Illegal logging in the forests of Mexico has been displacing clusters of the Monarchs, leading to a loss of winter habitat.
As climate change continues, the extinction of these butterflies has become more likely. Restoring the forests and increasing the extent of habitat by planting milkweed that is native to the local area, the monarchs population can be increased. Reducing the use of herbicides on milkweed will ensure their availability for monarch butterflies so that their caterpillars can feed on them and butterflies can lay eggs on them. Last but not the least, unless we reduce greenhouse gases emissions and tackle climate change effectively, we might not see these wonderful creatures in the next twenty-thirty years.