HMNS greenhouse teaches how to plant a butterfly oasis in your back yard

They float on the wind, decorate your back yard in the spring and summer, and inspire warm emotions with their delicate wings. They seem carefree, at home in any meadow, but butterflies have more specific needs than we might imagine.

monarch

Monarch butterflies don’t live just anywhere; they need habitat, too!

As urban sprawl continues to grow, reducing green space and native plant growth, natural butterfly habitats are shrinking. Butterflies require specific plants on which to feed and lay eggs. Caterpillars are finicky eaters.

Soni Holladay, Houston Museum of Natural Science Horticulturist and Greenhouse Manager, will lead a class Saturday, April 18, beginning at 9 a.m., to share information with the public about how best to plant a garden that will attract native butterfly species, creating a backyard butterfly nursery.

Holladay’s main concern is planting tropical milkweed to attract the famous migratory monarch butterfly. Though tropical milkweed is easier to grow, scientists have discovered it may play a part in declining monarch populations.

A parasitic species of protozoan called Ophryocystis elektroscirrha, or simply Oe, grows on the body of their monarch hosts. When infected monarchs land on milkweed to lay eggs, Oe spores slough off and are left behind. Caterpillars, which eat the milkweed, ingest the spores and become infected.

When the protozoans become too numerous, they can overwhelm and weaken individual butterflies, causing them to suffer. Several heavily infected monarch can take a toll on the local population. Oe can kill the insects in the larval or pupal stage, as well, before they can reach full adulthood.

Asclepias_curassavica_(Mexican_Butterfly_Weed)_W_IMG_1570

Tropical milkweed survives the Houston winters, making them a perennial plant and a possible danger to monarch butterfly populations.

Native milkweeds die off every year and grow back in the spring Oe-free as part of their cycle, but the evergreen tropical milkweed remains standing year-round, providing a vector for the protozoan to spread.

“We’re advising everyone who plants tropical milkweed to cut it back once a year or more,” Holladay said. Much like their native cousins, the tropical variety will return later, a healthy habitat for butterflies.

Holladay’s class will offer more details about this and other butterfly-raising issues. After the class, guests will tour HMNS greenhouses and our on-site butterfly-rearing operation. Tickets $23, all ages. Native milkweed plants and other seeds will be available to get you started.

Why no tropical milkweed at the Cockrell Butterfly Center plant sale this year?

Asclepias_curassavica_(Mexican_Butterfly_Weed)_W_IMG_1570

Aslepias curassavica

We are sorry to disappoint monarch enthusiasts, but the Cockrell Butterfly Center has decided not to sell tropical milkweed (aka Mexican milkweed, Asclepias curassavica) any more. Instead, we will have a limited quantity of native milkweeds for sale. Recently, biologists studying monarchs have discovered that tropical milkweed may be a factor in the spread of a parasitic infection that attacks monarchs. The infection is called Oe (short for Ophryocystis elektroscirrha) and is transmitted by spores that fall from an infected female’s body onto the hostplant when she lays her eggs. The hatchling caterpillars eat the spores along with the leaves, and become infected themselves. After a generation or two or three, the infection level becomes so high that the butterfly dies (sometimes in the caterpillar stage, sometimes in the pupal stage, and sometimes as the adult).

This could happen with any milkweed – the problem with the tropical species is that it does not senesce (die back) in Houston’s mild winters but is perennial, growing throughout the year. In contrast, native species die back to the ground in the winter, and when they regrow in the spring they are spore free – so the infection cycle is broken.

Also, researchers have found that some monarchs in the southern part of the USA don’t bother to migrate if they have milkweed available. These year-round residents have been found to have very high levels of Oe infection, because they are mostly using the tropical milkweed species generation after generation. While this probably doesn’t greatly impact the migration as a whole, we don’t want to contribute to the local spread of the disease.

If you do already have tropical milkweed, one solution is to cut it back severely a couple of times a year. Even better is to remove the tropical variety and switch to native milkweed species. Unfortunately, so far these are not widely available in the nursery trade and are not as easy to grow as the tropical variety!

Aslepias viridis

Aslepias viridis

We are all learning and struggling to do our best for the butterflies. This year we will have a limited quantity of two native species at our spring plant sale: Green Milkweed (Asclepias viridis) and Antelope Horns Milkweed (Asclepias asperula).

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Our next plant sale will be Saturday, March 28, 2015 from 9 a.m. to noon, or until we sell out. It will be located in its usual spot on the 7th level of the Museum parking garage. We hope you will try growing native milkweeds, and please let us know how it goes for you!

Tired from a long journey, faded monarchs seek homes for the next generation

My friends Bob and Bev photographed this very faded, tattered female monarch flying around the milkweed plants in their backyard near the Museum last week. The butterfly is a migrant from Mexico, looking for places to lay her eggs as a last hurrah before she dies.

Detail of a healthy monarch’s wing

The monarch we found with faded, damaged wings

The monarch we found with faded, damaged wings

She must be very tired!

Last fall, she flew from somewhere in eastern North America all the way to central Mexico, where she spent the winter mostly in hibernation. A few weeks ago, she and the other overwintering butterflies, sensing the lengthening days and warming temperatures, left the shelter of the sanctuary’s trees and headed back north to complete the journey. They are just now getting to Texas.

This old girl’s eggs will hatch and — if they have enough milkweed — the caterpillars will mature and pupate. Then, when they emerge as adult butterflies, at least some of them will continue the journey north. By July, monarchs will have reached the northern limit of their range. These summer generations don’t live as long, and don’t travel nearly as far.

P1070759If you see worn and faded monarchs at this time of year, they are almost certainly migrants returning from their winter in Mexico. You can help them to fulfill their “purpose” by providing nectar for their last few meals, and more importantly, milkweed for the new generation. These returning migrants will only last a few days now that they’ve gotten here — they are on their last “wings” after nearly nine months of life, and at least 2,000 miles of travel.

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A healthy Monarch Butterfly

Monarchs want YOU to plant milkweed: Butterfly-friendly plants for sale at HMNS

The butterflies need your help! With urbanization, and a host of other factors, monarch butterflies are at risk of not finding places to lay their eggs. So why not help while improving the butterfly traffic through your garden with a butterfly-seducing plant from our biannual plant sale?

Milkweed plants in the genus Asclepias are extremely important for butterflies, especially monarchs. While the blooms provide copious amounts of nectar for many different butterflies, the foliage is an essential part of the monarch butterfly’s life cycle. Milkweeds are the only plant monarch caterpillars will eat. In other words, they can’t live without it!

Native milkweed plants grow along roadsides and in open fields. The butterflies find them by honing in on their volatile chemicals and finally locate the exact plant by “tasting” nearby plants with special receptors called chemoreceptors on their feet. Once a gravid female (one who has mated and is ready to lay eggs) finds a good milkweed plant, she will lay eggs on it — and the miraculous process of metamorphosis has begun!

There are about 100 species of Asclepias in the United States, and over 30 in Texas — but monarchs seem to prefer some of them over others. According to a study by Linda S. Rayor, described in The Monarch Butterfly: Biology and Conservation, when given a choice, monarchs prefer to lay eggs on other species of milkweed over the native species Asclepias tuberosa.

Butterfly - Tropical Milkweed

Besides being a host plant for Monarch larvae, Tropical Milkweed (A. curassavica) is a great nectar source for many butterfly species!

Why? Different Asclepias species contain different cardenolide concentrations (cardenolides are the chemicals in the milkweed leaves that taste bitter). As they eat, the caterpillars store these toxic chemicals in their bodies and thus become distasteful to their predators. A. tuberosa has been found to contain low amounts of cardenolides compared to most other species of milkweed. Although it is unclear how monarchs “know” this, they do not usually use A. tuberosa as a host plant.

Several other native milkweed species, however, are great host plants for the monarch. Asclepias asperula (Antelope Horns), A. viridis (Green Milkweed), A. incarnata (Swamp Milkweed) and A. oenotheroides (Zizotes Milkweed) are some of the more commonly found milkweed plants in our area that monarchs use as host plants.

Unfortunately, most of the native milkweeds are hard to find in plant nurseries. One reason is that their seeds require moist stratification to germinate, and even with this pretreatment, germination can be splotchy. Furthermore, young plants of A. asperula, viridis and oenotheroides take several seasons to establish their thick taproots, and can be hard to transplant.

On the bright side, most of the native milkweeds, except for A. incarnata, are drought tolerant and can handle being mowed. Swamp milkweed obviously likes moist soil. All milkweeds grow best in full sun.

Butterfly - Green Milkweed

Asclepias viridis, Green Milkweed

Most gardeners are familiar with tropical milkweed, or Asclepias curassavica. This plant is commonly available in local plant nurseries and attracts butterflies like a magnet! Its bright orange and gold flowers are irresistible to many butterflies, and the high levels of cardenolides in its foliage make it especially sought out by female monarchs looking for a place to lay their eggs. Although it originates in more tropical climes, it is relatively cold hardy and will usually come back from the base of the plant after a freeze. It is also easy to propagate from seed, and in fact will sometimes seed out (make more of itself) in a garden.

So tropical milkweed seems like the ideal plant. However, one issue with this species is that it is not native to our area and does not exhibit the same characteristics of our native milkweeds, all of which die back to the ground in winter. This perennial habit seems advantageous, but it can be a problem for a couple of reasons. Because it has leaves year-round, it may encourage monarchs to overwinter locally instead of migrating to Mexico. It can serve as a host for a disease that affects monarchs, called Ophryocystis elektroscirrha, or simply O.e. This disease is caused by a protozoan parasite and is spread in the dormant stage of its lifecycle as a tiny spore.

These spores are typically on the abdomen of an infected monarch butterfly and can be spread to her eggs or onto the milkweed plants themselves when a female lays eggs. Then, when the caterpillars hatch out of the eggs, they consume the spores that lie on their empty egg shells or on the leaves around the egg and become infected.

Over a few generations, the parasite load can build up to high enough levels that it impacts the butterfly’s survival. Depending on the severity of the infection, the disease can make the caterpillars look a bit grayish and their stripes not as distinct. When the caterpillars pupate, their chrysalis may look brownish or spotted. The butterfly inside may emerge but have problems, such as an enlarged, gray abdomen and weak, faded wings.

Sometimes they emerge and look healthy, but secretly harbor O.e. spores on their abdomens. Other times they don’t emerge from the chrysalis at all, or get stuck while trying to come out.

So what is my point? I thought we were talking about milkweed plants! 😉 The reason this is important is because O.e. spores persist on the leaves of the tropical milkweed plants, waiting for an unsuspecting caterpillar to munch them up. To break this cycle, we recommend cutting your tropical milkweed plants back after a monarch generation has stripped their leaves, especially in the spring and fall. A simple pruning of the plant’s stems about six inches from the ground will get rid of any remaining spores and will sprout new growth in no time.

Some other closely related plants that monarchs will use as a host are Gomphocarpus physocarpus or “family jewels” milkweed, and a species of Funastrum or twinevine. Gomphocarpus is a lot like A. curassavica in that it doesn’t lose its leaves in the winter so it also needs to be cut back periodically to keep it from spreading O.e.

Butterfly - Funastrum cynanchoidies flower

Funastrum cynanchoidies flower

Funastrum or twinevine is an interesting climbing plant native to south Texas and Mexico. The plant is not very impressive looking until the summer, when it puts on beautiful balls of milkweed-like flowers that are great nectar sources for many kinds of butterfly. Another good thing about it is that when monarch caterpillars have stripped all your milkweed plants of their leaves and are still hungry, they will eat the leaves of Funastrum.

With their habitat dwindling due to urbanization, the use of Round Up ready crops, shrinking right-of-ways due to intensive agricultural practices and other factors, monarch butterflies need all the help they can get. The take-home message today is PLANT MORE MILKWEED! (please)

For milkweed and other awesome butterfly host and nectar plants, come visit us at our biannual Spring Plant Sale on Saturday, April 5th from 9 a.m. until we sell out! We are located on the 7th level of the Museum parking garage. Parking is free if you spend $30 or more!

Come early, the plants go fast!