Threats to Monarchs

One of the primary threats to monarch butterflies is the threat of deforestation. Deforestation is exactly what it sounds like - it is the process of "deforesting" forests, specifically by removing trees from forests. This activity has been increasing in the forests of Mexico and California. This causes less trees to be available for monarch butterflies to shelter in, reducing space for monarch butterflies to rest during their migration paths. As a result, monarch butterfly populations deplete.

When humans spray pesticides on host plants for monarch butterflies (milkweed), they add an extra level of toxicity to the milkweed. Even though monarch butterfly larvae can withstand the poisonous milkweed sap of the plant, they cannot withstand the toxicity of the pesticide being applied to the milkweed plant. This makes milkweed harmful to monarch caterpillars to eat, causing monarch caterpillars to die, depleting monarch butterfly populations. In addition, the use of pesticides to kill milkweed plants causes a significant depletion in the amount of host plants available for monarch caterpillars to eat and for female monarch butterflies to lay their eggs on. This is another reason why the use of pesticides on milkweed plants is a major threat to monarch butterflies.

When humans release greenhouse gases into the atmosphere through combustion such as driving cars and emitting air pollutants from smokestacks in factories, more greenhouse gases are released into the atmosphere. The increase in these greenhouse gases causes more sunlight reaching the Earth to be re-radiated back to the surface of the Earth. This increases the Earth's global temperature, causing shifts in weather patterns in a phenomenon known as global climate change. Sometimes, these shifts in temperature have opened up new environments for pathogens and parasites to colonize, proliferating infections by these creatures. For monarch butterflies, a fungus known as Ophryocystis elektroscirrha (O.E) has taken advantage of the warmer climates and spread into monarch butterflies. This parasite infects and grows inside the bodies of monarch butterflies, causing severe and often fatal infections in the pupal stage for these butterflies. If these infections are not fatal, then monarch butterflies often hatch out of pupas severely deformed (Project Monarch Health 2019).