Monarch Basics
Did you know?
You will commonly hear people referring to "western monarchs" and "eastern monarchs" - but there is only one species: Danaus plexippus, the majority of which can be found in North America. The Rocky Mountains create a natural dividing line which runs from Canada through the US and into Mexico. They separate a much smaller quantity of monarchs in the west from the majority of monarch population east of the Rockies. This may be due to a better climate for healthy breeding habitats in the east.
SIGNIFICANT DECLINE
Scientists have been documenting monarch populations since the 1980's or before. Beginning in the 1980's, they saw a significant decline in numbers, which happened to correspond with the mass use of herbicides by farmers and homeowners.
Development that displaces healthy breeding and overwintering habitats, as well as climate change, are now driving the population decline.
in 2020, the annual Western Monarch Count only recorded 1,014 monarchs... down from the 1.2 million recorded in 1997, and down from more than an estimated 5+ million in the 1980s.
The 2023 overwintering count in Mexico is so massive they count in the amount of forest that is covered in monarchs. Experts just recorded the second-to-lowest number of monarchs recorded since they started counting, at less than a hectare (2.47 acres), down from 45 hectares (111 acres) at their peak.
While the population has rebounded to more than 200k since 2020, experts say that number isn't enough for a sustainable population west of the Rockies.
They need our help.
Overwintering in Pacific Grove, CA - Dec. 2021
Some Monarch Basics
North America is the primary home of monarch butterflies. The majority of the population lives east of the Rocky Mountains, with a much smaller population west of the same. They are all the same species, just split by those magnificent Rocky Mountains, which funnel the fall migration in different directions: western monarchs head to the California Coast; eastern monarchs head to the high mountain areas of Mexico.
Monarch butterflies spend their summers searching for healthy breeding habitat (milkweed, nectar sources and water), which brings them north and northeast across the US, with four (sometimes five) generations. Monarchs reach as far as British Columbia in the west, and Ontario, Canada in the east.
The first new generation of the year reaches Utah in May, and their newly laid eggs hatch about 30 days later. This 2nd generation of the year stays in Utah, breeding and laying eggs for 3-5 weeks. Generations 3, 4, and sometimes 5 follow depending on the weather.
In August through September, those emerging from chrysalis across the US are the great migrating generation. They hit the pause button on breeding to save their energy for a journey of up to 3,000 miles. They must head to warmer climates to stay warm enough to survive the winters. They must survive on nectar from pollinator plants they find along the way, living off their body fat over the winter. Based on the data reported, we know that monarchs in Utah go to both overwintering sites - Mexico and California.
Beginning in March, these monarchs sense it's time to breed and start migrating back to the US to find milkweed to lay their eggs. 30 or so days later, the first new generation of the year is born, and the migrating generation ends its extra-long lifespan of 7-9 months; all other generations live just 3-5 weeks.
Monarchs grow from egg to caterpillar, chrysalis to butterfly. This process can go as quickly as 22 days in the heat of the summer, or take months during the colder seasons. See graphic to the left.