The monarchs have returned to Texas

Monarch butterfly, probably male

Actually, they returned over a week ago. I believe I saw my first monarch of the year April 1st. It was a female, hopping from milkweed to milkweed. She deposited one egg on each plant. One of her cousins was doing the same nearby. I was impressed with how she homed in on each plant, wasting no time in the search.

side-cluster milkweed w/egg

 Monarch butterflies are incredibly widely distributed, and are found in all lower 48 states.  They even introduced themselves to Hawaii. The Hawaii population is especially unusual because they have developed a unique white morph in contrast to the bright orange we see on the mainland. However, the two major populations are found in the lower 48 states. They can be further split into the western population (approximately 5% of total), and the eastern population (most of the remainder). The eastern population is the subject of the listing petition, and it is the group we see in Texas. This group has seen a 90% decline in overwintering numbers in the past 20 years. While monarchs as a species are secure, this eastern migration is an endangered biological phenomena.

Monarchs have a peculiar life history.  The first 3-4 generations of the year live approximately 4 weeks and grow and reproduce like a standard butterfly. They follow the fresh milkweed and flowers north as the season progresses. However, the last butterflies of the year to hatch live 6-9 months and migrate thousands of miles south from the Upper Midwest to Mexico. These butterflies are in reproductive diapause- that is, they don’t breed- and they focus their energy on gliding south in September, October, and November.  Once they hit Texas (generally in October), their migration slows. Instead they feed, intent on gathering enough fuel to support themselves during the 6 months they spend overwintering in the oyamel fir forests in the mountain highlands west of Mexico City.

Monarch ovipositing on milkweed

The monarchs arrive at their overwintering grounds in Mexico around the first of November most years. Their arrival coincides with the Day of the Dead celebrations, and monarchs are taken to represent the visiting souls of departed loved ones. Once the monarchs arrive, they become dormant and roost in high density “shingles” entirely coating the trees in their chosen forests. They don’t feed or breed, and spend most of their time resting on the branches and trunks of these oyamel firs. It is at this time that the monarchs are counted. Because the monarchs roost socially in high numbers, you can get a population estimate based on the area occupied. The lowest ever numbers were recorded in the winter of 2013, when the entire eastern population, ~95% of the world’s population, only occupied 1.7 acres.

Fresh monarch egg

By mid-March, spring returns to the Mexican highlands and monarchs break dormancy. They mate and begin their migration north. Monarchs return to south Texas in late March, making the thousand mile trek from Mexico in about a week. Once they reach Texas, they search out fresh milkweed sprouts on which to lay their eggs.  It was these tired, 9 mo old females I observed ovipositing earlier this month. After breeding, this generation dies. It is their offspring which continue the journey north to recolonize their North American range. Each subsequent generation moves a little farther north, until September when the “methuselah” generation hatches and the cycle begins again.

2nd instar monarch caterpillar

Texas is crucial to the monarch habitat for two periods of the year- those first monarchs returning to the states, and the last generation to leave. In March and April, the returning females nectar on wildflowers and lay their eggs on milkweed, the only food plant which can support their caterpillars. Texas becomes important again in September and October, when migrating monarchs stop to re-fuel on wildflower nectar before their long slumber in Mexico. Without nectar in the fall, these monarchs will not survive the winter. Without milkweeds in the spring, their offspring will starve. We can support monarchs as they funnel through our state by planting milkweed and fall blooming nectar plants. We cannot control what happens to these butterflies across the entirety of their range, but by working in our own backyards we can support the start and end of their migration.

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Photo credits: Figures 2 & 4: Philip Barbour, CNTSC; Figure 1 & 3: Anne Stine; Figure 5: Rosanna Brown, CNTSC.