Researchers who monitor the annual migration of the western monarch butterflies that migrate along the California coast have noticed that the population of these migratory insects has declined at an alarming rate.

Substantial Decline In The Number Of Migrating Monarch Butterflies

In 1981, the nonprofit environmental organization Xerces Society counted more than 1 million western monarchs wintering in California.

The group's most recent count over the Thanksgiving weekend, however, recorded less than 30,000, or an 86 percent drop from the number recorded in 2017, when the Western Monarch Thanksgiving Count (WMTC) recorded 193,000 monarch butterflies wintering California's Pacific Coast.

Xerces Society described the number, which has been reduced to less than the 0.5 percent of the historical size, as "disturbingly low" and potentially "catastrophic."

"In 2017, these sites accounted for 77% of the total monarch overwintering population, hosting approximately 148,000 monarchs. In 2018, the same sites have only 20,456 monarchs. This represents an 86% decline since last year," the Xerces Society said in a statement.

Cause Of Plummeting Population Of Monarch Butterflies

The organization is not certain what caused the number of the monarchs to substantially plummet in its most recent count.

Nonetheless, aside from the downward population trend fueled by use of pesticides, herbicides, and destruction of the monarchs' milkweed habitat, scientists suspect that the declining population observed in the latest count is linked to the butterflies arriving nearly a month late to their breeding areas last year. This left the aging monarchs more exposed to the elements.

The black and orange butterflies did not even make it to their breeding range in the Washington state, where they are typically abundant.

The organization also said that there is insufficient evidence of delayed migration. The butterflies are neither sighted in other parts of the country.

Monarch Butterflies At Risk Of Extinction

Researchers have been sounding the alarm that the species could be at risk of extinction. They believe that the monarch butterfly needs to be listed as a threatened species under the Endangered Species Act so everyone will participate in conservation efforts to protect these butterflies.