Texas Plays a Unique Role in the Annual Monarch Butterfly Migration
October is time for the fall monarch butterfly migration! Each year millions of Monarch butterflies make a 3,000 mile trek from the Northern U.S. and Southern Canada back to their breeding and over-wintering grounds in the Oyamel Forest in Central Mexico. In order to get there, they will pass through "The Texas Funnel" along the way. In fact, nearly 40% of all Monarchs in North America pass through Texas gardens during their lifespan!
With the total Monarch population in steep decline, Texas gardeners have a chance to make a huge difference in the long term health and wellbeing of our nation's endangered pollinators.
This article discusses how to build a Monarch garden, including what plants and other features you should offer to sustain them on their remarkable journey.
As the nearby picture shows, you don’t need to have a huge garden to provide a rest stop for them as they make their annual journey through Texas. This small bed right outside our greenhouse has everything the Monarchs need in that one little space.
Read on to learn about some of the many resources available to make Monarch watching more fun for you and your kids or your grandkids.
Rather watch it on video? Here it is:
Monarchs In Decline
The total Monarch population living east of the Rocky Mountains used to number in the hundreds of millions but since the 1990s the population has declined by approximately 80%. Loss of habitat and pesticide use are two major causes of monarch decline.
You may think that a single backyard pollinator garden isn't significant, but consider this: Many conservation groups have been working together with farmers, ranchers, park and natural areas managers and gardeners across the eastern U.S. to plant milkweed and nectar plants needed for the monarch’s survival. Through programs like the Million Pollinator Garden Challenge, Americans have been able to reestablish millions of acres of native habitat. So when you build a pollinator-friendly garden, you are contributing to that habitat restoration effort.
Pesticides & Herbicides
But none of this makes any difference if all those acres are sprayed with chemical pesticides and herbicides. Butterflies are extremely sensitive to chemicals. Even some organic insecticides are harmful to them. The product may not kill them outright, but can also cause birth defects in their young. So once you've decided to garden for Monarchs, the first and most important thing to do is stop using pesticides and herbicides.
When you consistently follow an organic program, you should be able to rely on beneficial insects and other garden predators to keep your lawn and beds in a natural balance. If things do get out of control and you have an infestation, you can often just release more beneficial insects – like ladybugs and praying mantises – to bring it back under control. If you feel you must treat with a pesticide, instead of choosing a general-purpose product that kills all insects, choose the one that does the least amount of damage.
You can also help minimize harm by the way you apply the product. For example, when you spray a plant, carefully cover each flower by cupping your hand over it so that the product doesn't contaminate the nectar source.
Note: You can learn more about how to maintain a chemical-free garden by visiting our store, reading our blog, subscribing to our email list, and by attending our educational classes.
How Monarchs Breed
Male Monarchs have two spots on their hind wings – one on either side of the body. Females have no spots but do have thicker veins than the males.
After they mate, each monarch female lays only 1 egg per plant, so if you see multiple eggs on a plant, that means you’ve had several visitors. One of the things that make Monarchs special is that they will only lay their eggs on Milkweed plants.
Adult butterflies of all types live by drinking flower nectar, but curiously, Monarchs do not usually drink Milkweed nectar -- probably to help ensure that more of the plant’s energy can be allocated to the caterpillar. So the Monarch's survival depends on Milkweed and Milkweed is dependent on native bees like Mason bees, and pollinating wasps, for its survival. That hopefully gives you an idea of how complex and interconnected our native habitats are.
When the egg hatches, a caterpillar emerges. It then goes through 4 distinct phases – also called “instars” -- before it’s ready to pupate.
Pupating is the process they go through when they are ready to build their Chrysalis. Some people use the words Chrysalis and Cocoon interchangeably but to be correct, Moths make cocoons. Butterflies make Chrysalises.
A monarch spends 8 to 15 days in its Chrysalis. The butterfly's beautiful orange and black wings appear the day before it finally emerges as an adult butterfly.
The whole process takes about 30 days.
Those monarchs belonging to the the Northbound generation live for two to six weeks as adults, but the hibernating generation that roosts in the Mexican mountains can live for up to nine months. They remain in hibernation from November through March and emerge to reproduce in the spring.
How They Live
Once the hibernators reproduce, they die, leaving their children to carry on. The new-born butterflies quickly start looking for nectar and Milkweed plants in order to keep the cycle going.
So back to the Asclepias family. . . There are over 100 milkweed species that are native to North America, many of which are used by monarchs. Which of these you should plant for your Monarchs is different for North Texas than it is for, say, Washington state or New Jersey, or Central Mexico. Unfortunately most Texas growers primarily produce tropical milkweed, which isn’t even native to our area. It is more cold sensitive than the some varieties, so it doesn’t always come back the next year. While this isn’t all bad, it tends to result in a lack of plant diversity and that lack of diversity is reflected in the Monarch’s diet. One danger is that if for some reason something devastated the tropical milkweed supply, Monarchs would have nothing to fall back on. Finally, each type of milkweed has a special contribution to make to our environment.
Here are the best types of Milkweed for North Texas:
Butterfly Weed (Asclepias tubersoa)
Also called Orange Milkweed, this perennial has large, flat-topped clusters of orange or yellow flowers.
Blooms May to September
Growing Conditions: Full sun and dry or lightly moist soil. It is highly drought tolerant.
Height: 1 to 2 ft.
Swamp Milkweed (Asclepias incarnata)
Also known as Pink Milkweed, this perennial has large blossoms of small, rose-purple flowers clustered at the top of a tall, branching stem.
Blooms June to October
Growing Conditions: Needs lots of water. Prefers partial shade and moist to wet soil
Height: 2 to 5 ft.
Notice the differences in plant height, moisture and sun requirements, and bloom times between these two varieties. Butterfly weed likes hot, dry spots – it is adapted for living out in the middle of the prairie. Swamp milkweed likes moist soil. In the wild it grows around the edges of lakes and ponds. It also needs lots of shade.
Showy Milkweed (Asclepias Speciosa)
This perennial has large, oval, blue-green leaves and spherical clusters of rose-colored flowers. The flowers occur at the top of the stem and on stalks from leaf axils.
Blooms May to September
Growing Conditions: Prefers full sun but will tolerate partial shade and moderately moist soil.
Height: Usually 2 to 3 ft but can reach 6 ft under favorable conditions.
Antelope Horns Milkweed (Asclepias asperula)
Spider Milkweed, as it is also know, is a clumping perennial with stems that are densely covered with minute hairs. As the green seed pods grow, they curve to resemble antelope horns. It has pale, greenish-yellow flowers, tinged maroon.
Blooms March to October
Growing Conditions: Full sun and dry soil. Drought tolerant.
Height: 1 to 2 ft.
Green Milkweed (Asclepias viridis)
This perennial is very similar to Antelope Horn -- so much so that it is also called Green Antelope Horn Milkweed, except that its white flowers lack the “horns” seen on true Antelope Horn Milkweed. Green Milkweed is common in pastures from Kansas to Texas. Generally avoided by cattle and horses, it can be found along roadsides, ditches, prairies, open areas, and other areas with little vegetative competition.
Blooms May to August
Growing Conditions: Full sun. Cold, heat and drought tolerant.
Height: Up to 4 ft.
Whorled Milkweed (Asclepias verticillata)
Unlike the other Milkweeds above, Whorled Milkweed has narrow, linear leaves that whorl along the stem. A perennial, it has small, greenish-white flowers occur in flat-topped clusters on the upper part of the stem.
Blooms May to September
Growing Conditions: Prefers full sun and dry soil but will tolerate moderate shade. tolerant.
Height: 1 to 3 ft.
Again, notice the differences between the various varieties. Antelope Horns Milkweed starts to bloom much earlier than the other varieties beginning in early March when Monarchs are just beginning to arrive from their over-wintering areas. It continues to bloom into October as Monarchs are heading back to their over-wintering grounds.
By comparison, Showy Milkweed and Butterfly Weed don’t begin blooming until May when there is a larger number of monarchs in the area. Finally, Swamp Milkweed comes out last in June as most monarchs have reached their summer foraging ranges.
Warning: Do not spray Milkweed plants with any type of insecticide or herbicide as these can kill the adult butterflies and/or cause birth defects in their young.
Download our list of Milkweed Plants for North Texas
Nectar Plants for Adults
A lot of butterfly gardeners focus on providing Milkweed but we also need to think about providing habitat for the adults. That means offering nectar plants as well as water and shelter. There are a huge number of annuals, perennials and shrubs to choose from, and the more variety you can offer, the better.
Download our list of Butterfly Nectar Plants
Since Monarchs are on the move essentially from March through October, it is important to provide forage for them continuously during this time. But few plants bloom over this entire period. While some nectar plants might bloom for 2 or months, other plants only bloom for 2 or 3 weeks in the spring while others only bloom in the spring. This makes it important to have a variety of plants that bloom at different times so that there is always something available to them.
It is also always preferable to plant native plant species rather than exotics or other non-natives because non-native plants don’t sustain our native insects as well as native plants do.
Note: Use care when spraying nectar plants with pesticides or herbicide. Prevent any overspray from getting on the flower and contaminating the nectar.
What Makes Monarchs Migrate?
The monarch is the only butterfly known to make a complete two-way migration as birds do. But the southward migration in the fall is very different from the northward one in the spring. This annual phenomenon is one of the most incredible things in nature! Especially since the Monarchs making the southbound journey are not even the same ones that migrated north in the spring.
So where exactly are all these butterflies are coming from and where are they going?
This map from the Xerces Society shows all the migration routes followed by Monarchs. There are two separate and distinct migration paths. Those that live West of the Rocky Mountains migrate up and down the West Coast and those that live East of the Rock Mountains. Western Monarchs overwinter in California along the Pacific coast near Santa Cruz and San Diego. Eastern Monarchs form one much larger group that spreads out over the other two thirds of the U.S. Texas monarchs are all part of that Eastern group.
Eastern Generation 1 Monarchs are born in the Oyamel Forest in Mexico. They are the offspring of the monarchs made the southern migration the previous fall. Their parents – the ones that overwintered there -- die soon after laying their eggs. Generation 1 travels about 1/3 of the way to their summer grounds in the Northern U.S. and Southern Canada, or about 1000 miles, which takes them through Mexico and into Texas, where they then spread out and across the southeast.
Once they arrive in Texas, they start fanning out in search of Milkweed to lay their own eggs and parent Generation 2. Each successive generation travels farther north. It takes 3 to 4 generations to reach the northern United States and Canada.
Generation 4 – those monarchs that emerge after about mid-August enter reproductive diapause (do not reproduce) and begin to migrate south in search of the overwintering grounds. That group of monarchs has to travel the entire 3,000 mile distance from their summer foraging grounds back to Central Mexico. And they only have about 3 months to get there!
Another truly amazing aspect of the migration is that all Eastern monarchs converge on Texas as they travel back and forth to their winter home. They use the same 4 well-established flyways on their way back south, merging into a single massive group again in Central Texas commonly called "The Texas Funnel". It is truly amazing that these monarchs know the way to the overwintering sites even though this migrating generation has never before been to Mexico!
Ultimately, 40% of the total Monarch population of North America passes through North Texas! Interestingly, the three prongs of the migration path closely follow the same paths as our major North-South highways.
For example, the center red line corresponds to the I-35 Corridor. The right hand fork corresponds to the I-69 corridor and the left fork parallels I-29. These are the same routes are followed by other migratory species, including, ducks, geese, other migrating insects.
Every year, scientists, citizen scientists and monarch butterfly enthusiasts track the migration. By tracking monarch sitings within each of these bands, they can estimate when the butterflies will arrive in the next area and when the bulk of the population has passed through. According to Monarch Watch this year’s migration should reach Texas around the beginning of October and continue through the end of the month, peaking around 10/15. Monarch sitings have already been made around North Texas over the last week or two, so now is when you should get out and look for them.
As mentioned previously, the Monarchs that make the southbound journey are not the same ones that migrated north. So how do Generations 3 and 4 know when it’s time to head south?
Scientists aren’t entirely sure, but we know there are several signals. The reproductive diapause phase that some Monarchs experience is one Decreasing day length and cooler temperatures are also a nudge.
But how do they know where they’re going?
Some scientists believe that Monarchs have a built-in magnetic compass that keeps them on course to their overwintering location. One research report showed that migratory Monarchs do indeed have a magnetic compass on board. Monarchs have solar receptors in their antennae that provide both a timing cue and a directional sensor. The receptors sense the shorter days and, they think, also measure short wave UV-light which helps them know which way is south.
They may also have another type of compass. Monarchs can only fly during they day. At night they congregate together in trees to sleep. So one possibility is that they have a “Sun Compass.”
A sun compass measures the angle of the sun and could point the way to the overwintering sites. In this scenario, Monarchs use the angle of the sun along the horizon in combination with an internal body clock (like a circadian rhythm) to maintain a southwesterly flight path.
However, a sun compass alone wouldn’t work because, if all the monarchs in eastern and central North America maintained a southwesterly flight, they could never all end up in the same place. So scientists suggest that the butterflies may also use landmarks like mountains. The idea is that a mountain range would funnel the Monarchs in the right direction toward Mexico.
Some speculate that the course Monarchs fly is influenced by terrain. As they approach Texas, for example, they are funneled together by two barriers -- the Gulf of Mexico on their left and the Rocky Mountains/Sierra Madre Orientals on their right, i.e., The Texas Funnel. Monarchs avoid flying over open water and are able to find the shortest distance across them to reach their destination. When they do need to fly over water, they wait for gentle breezes to help them across.
There are noticeable genetic differences between Eastern and Western Monarch populations. There is also a small population of non-migrating Monarchs that live in Florida which have another distinct genetic signature. But so far no one has identified a "migration" gene.
However they do it, they are amazingly accurate!
The 3-month long journey requires daily rest stops. Monarchs travel about 100 miles per day and they can only travel during daylight hours. Needless to say, they need to eat a lot to maintain their energy levels. Residential and community gardens play an important role in keeping them going.
At night they sleep. Each evening, they gather close together to roost for the night. Roosting sites are important to the monarch migration and many are used year after year. They often choose pine, fir and cedar trees, probably because these trees have thick canopies that moderate temperature and humidity.
Tens of thousands of monarchs can cluster on a single tree. Clustering together like that helps them stay warm.
Once they reach the Oyamel Forest they crowd together in the trees on the south-southwest facing mountain slopes where they can enjoy cool temperatures, water, and protection from predators for the winter.
In March, the cycle starts all over again.
Become a Citizen Scientist
Butterfly gardening is rewarding and healthy. Not only is it relaxing but it also boosts your immune system, reduces stress, and helps you feel connected to nature. Besides growing a garden, adults and kids alike can also help monarchs by participating in some of the many citizen science programs aimed at conserving and restoring habitat. For example:
Join the Million Pollinator Garden Network and register your garden as Monarch habitat.
Show off! Get a sign to let others know your garden is a Monarch Waystation.
Help track the Monarch migration by volunteering to tag Monarchs you find in your garden.
Report your Monarch sitings and learn more about Monarchs at Journey North.
Now get outside and enjoy our beautiful fall weather!
Copyright 2020, Marshall Grain Co.