By Eric Duran
When I think of a butterfly, it is the Monarch that I imagine. I suspect that for many of us who grew up in the U.S., it may be the first butterfly we remember seeing as children or the first butterfly whose name we learned. My earliest memory of butterflies is watching Monarchs flutter around my mother’s garden, feeding on honeysuckle. Texans have such a strong affinity for this butterfly, that we made it our state insect in 1995.
Monarchs are large orange and black butterflies. Like most butterflies, they feed on nectar from a wide variety of flowers — but they will only lay their eggs on milkweed. Their larvae, caterpillars, will only eat milkweed. As a matter of fact, once the caterpillars start feeding on one species of milkweed, they will not feed on other species. So if you run out of Tropical Milkweed, you can’t move them over to Green Milkweed (so whatever species of milkweed you grow, try to get a lot of it).
Milkweed is toxic, and so are the Monarch caterpillars that feed on it. They carry this toxicity into adulthood, and so, unlike other edible insects, these would make you sick. The orange and black coloration of the adult butterfly is a warning to potential predators, like lizards, birds, and other insect eaters.
There are two major populations of Monarch butterflies in the U.S. — the Eastern Monarch and the Western Monarch. These populations are two different subspecies, and both are migratory. There are smaller non-migratory populations of Monarchs throughout the U.S., including Hawaii. The Western Monarch lives west of the Rockies during the breeding season and migrates to Southern California in the fall, to overwinter. The Eastern Monarch lives east of the Rockies, and overwinters in Mexico.
The Eastern Monarch has been extensively studied for its multi-generational migration pattern. Every year, it takes four generations of Monarchs to complete the entire migration pattern. In mid spring, the fourth generation from the previous year, who overwintered in Mexico, returns to breed in the southern U.S. Their offspring will hatch out later that spring (the first generation for that year), and then migrate further north, breed, and then die. Their offspring (generation 2) grow up, migrate further north, breed and then die — and so on, until the fourth generation hatches out in the far northern U.S. and southern Canada.
This is the longest-lived of the four annual generations. The fourth generation is the group which will migrate all the way back down to Mexico, where they will overwinter. As they migrate down in the fall, Bellaire and West U are on the route as many millions of them pass along the Gulf Coast of Texas on their journey south.
You may have noticed that we seem to have Monarchs here year-round, especially if the weather remains relatively mild that year. There appears to be a “fifth generation” that lives along the Gulf Coast of Texas that is non-migratory. It is not fully understood where this fifth generation came from, or how it maintains itself, but we have a relatively good idea of how it works.
Biologists believe that this generation are the offspring of Generation 4 as they pass through the area on their way down to Mexico in October. Now, historically, this would not have been possible as most of the native milkweed in our region has died back to the roots underground by the fall. However, over the past several decades, the garden industry has provided us with a hardy year-round species of milkweed native to Mexico and Central America, Tropical Milkweed, Asclepias currisavica.
So this new generation of Monarchs is only possible as a steady phenomenon year after year because of our penchant for growing non-native plants, specifically Tropical Milkweed, in our gardens. It’s not well understood what effect this modern Monarch population has on local ecosystems, but we do know that this generation is usually somewhat more diseased than the more “natural” populations.
Pathogens build up on the milkweed throughout the year as many Monarchs and other butterflies visit the plant, and then pass on to the fifth-generation caterpillars. These pathogens can also pass to migrating butterflies.
Personally and professionally, I would suggest that you not grow Tropical Milkweed, and try to find native milkweeds that you can plant in your garden, which will naturally die back by mid to late summer. If you can’t find native milkweeds, cut back your Tropical Milkweed before the fourth generation migrates back through here in October. What they really need is not more breeding opportunities, but more native nectar producing plants to strengthen them through their journey. (You can scan the QR code at the top of this article or email me for a list of native Texas wildflowers that Monarchs will love.)
One of the reasons why we’re talking about Monarchs this month is that they will soon pass through this region of the country once again. The other reason is a bit sad, the IUCN, a large group of conservation biologists from around the world, has classified the migratory populations of Monarchs in the U.S. as endangered. The Western population has dropped precipitously, by up to 99 percent. This is extremely worrying.
The declines are due to habitat degradation/destruction and overuse of neonicotinoid pesticides. The Eastern population has also declined, but not as dramatically. Because of the complex multi-stage migratory pattern, it can be difficult to study their numbers. The surveys at some previous breeding sites seem awful, but the studies of their overwintering populations are less worrying.
Regardless of what the data ends up saying, there has been a steady decline in their numbers over the past few decades; whether it’s by 20 percent or far more, it’s not very clear yet. The U.S. Fish & Wildlife Service has decided not to declare the Monarch as officially “endangered” in the U.S. but is reviewing further data on the Eastern population.
While the numbers are studied, the Monarchs continue to decline, and they need our help. You can act by planting native milkweed as egg/caterpillar host plants and other native wildflowers as nectar sources. Have them planted and ready to go for spring and fall. Encourage businesses and institutions to plant native wildflower gardens on their grounds. Refrain from using pesticides, and try to encourage others to refrain, as well.
On a national level, we need to get rid of neonicotinoid pesticides. If you have any questions about native plant gardens or butterfly biology, feel free to email me at eduran@naturediscoverycenter.org.
Duran is the head naturalist at the Nature Discovery Center, 7112 Newcastle Dr. in Bellaire.
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