HMNS entomologist Erin Mills walks you through how to mount and display a butterfly in this 4-part video tutorial.
Part I: Supplies
Check back next week for Part II!
As the obligate host plants for monarch caterpillars, milkweeds are a staple in any butterfly habitat garden. However, milkweed is not just for monarchs! Many other insects call the genus Asclepias home, giving rise to the concept of a “milkweed village.”
Milkweed plants produce bitter tasting toxins called cardiac glycocides, and insects that eat milkweeds have evolved to use these to their advantage, sequestering the toxins in their bodies to protect themselves from predators. Most, if not all milkweed-eating insects have markings of black and orange or yellow, a type of aposomatic coloration that warns predators of their horrible flavor. If a predator such as a bird, lizard, or spider were to eat one of these insects, it would spit it out. The next such insect would be avoided, as its coloration would remind the predator of its foul flavor.
Most butterfly gardeners have encountered the bright yellow oleander aphid, Aphis nerii, which congregates on the new growth, flowers, and developing seed pods of milkweed plants. Aphids are phloem feeders, meaning that they suck the sap, along with the toxins, out of the plant’s vascular tissue.
The presence of these aphids on milkweed attracts a number of predatory insects. Ladybug larvae and adults (Hippodamia spp. and others) are important predators of milkweed aphids. Other small beetles such as mealybug destroyers, Cryptolaemus montrouzieri, and scale destroyers, Lindorus lopanthae, eat aphids along with other small sap-feeding insects. These beetles are interesting creatures in that their larval stage looks just like their namesake (i.e., mealybugs and scale, respectively).
The maggot-like larvae of syrphid flies also eat aphids, sucking their bodies dry. Syrphid pupae look like little brown or tan teardrops. If you notice these on your milkweed plants, leave them in place to ensure another generation of these beneficial flies.
Tiny parasitic wasps such as braconids lay their eggs in aphids’ bodies. The wasp larvae feed on the inside of the aphid until they pupate, then exit as an adult wasp through a tiny hole in the aphid’s exoskeleton. The leftover brown “shell” is called an aphid mummy. These mummies are a good sign that your aphids are being parasitized. Don’t worry, these wasps don’t harm monarch caterpillars.
With all of these great beneficial insects around, I hardly had to spray our milkweed crop at the museum with any insecticidal soap this year. However, if the aphid population on your milkweeds gets to be overwhelming, the best way to knock them back is to spray them off the plants with a sharp stream of water. Try to avoid damaging or knocking off any beneficial insects in the process.
Other “pests” of milkweed plants include the milkweed leaf beetle, Labidomera clivicollis. These chunky, orange and black beetles and their larvae feed on milkweed leaves.
Large milkweed bugs, Oncopeltus fasciatus, are also common in the southern United States. These oblong-shaped, sap-sucking true bugs are orange and black and mostly feed on the developing seeds, flowers and nectar of milkweed plants. They don’t usually cause much damage.
Now we come to the most familiar milkweed inhabitant – the monarch butterfly, Danaus plexippus. As we all know, monarch caterpillars eat voluminous quantities of milkweed leaves, and display the textbook aposomatic coloration of white, black and yellow stripes. Their chrysalids, or pupae, are a gorgeous jade green with gold lines and spots.
Here in Houston we sometimes encounter another milkweed visitor – the queen butterfly, Danaus gilippus. Queen caterpillars look very similar to the monarch, but they have three pairs of tentacles instead of the monarch’s two. Their chrysalids are also similar, but are a bit smaller and may sometimes be a pale pink rather than green.
Like everything else, monarchs are part of the food chain, and are preyed upon or parasitized by a number of different organisms. One of their most prevalent parasites is a tachinid fly, a gray, hairy species about the size of a house fly. An adult fly female will lay her eggs on a monarch caterpillar and when they hatch, the maggots burrow inside. The maggots live inside the caterpillar, eating its tissues, until they are ready to pupate. At that point they crawl out of the caterpillar and fall to the ground, where they pupate in the soil The maggots often leave the caterpillar after it has pupated, leaving a trail of slime that dries up and looks like white strings hanging from the chrysalis. These strings are tell-tale signs of a tachinid fly infestation.
Assassin bugs, Zelus sp., are frequent visitors to milkweed plants. This true bug will stab monarch caterpillars with its rostrum or beak, paralyzing the victim and liquefying its insides, making it easier to consume.
Vespid wasps are another important predator of monarchs. The familiar large red wasps, Polistes carolinus, and the smaller yellow and black European paper wasp, Polistes dominulus, both hunt caterpillars as food for their own hungry larvae. Once a wasp finds a host plant with caterpillars, she will come back regularly to check for more, especially in the summer months when wasps are the most active. This can be upsetting to butterfly gardeners. To protect your caterpillars from these all-too-efficient predators, place a screen such as a pop up or mesh laundry hamper between them and the wasps.
Finally, a parasite of notable concern that specifically affects monarchs (and also queens) has emerged on the scene of butterfly gardening. This protozoan parasite, Ophryocystis elektroscirrha, commonly known as Oe, begins with a dormant spore, usually deposited by an infected female monarch as she lays her eggs on a milkweed. When the caterpillars hatch and begin to eat, they consume the Oe spores along with the leaf. Once inside a caterpillar’s gut, the spores become active and reproduce several times. When the butterfly emerges from its pupa, it is covered in dormant Oe. spores, giving rise to the next generation of infected monarchs. Mildly infected butterflies may show no sign of infection but as Oe levels build up, they eventually cause problems such as weakness, deformity, and even death.
The annual migration to Mexico each fall helps to weed out infected butterflies, which are usually too weak to make the long trip and die along the way. However, some monarchs don’t migrate and may stay in the Houston area all winter long. In the south, butterfly gardeners primarily grow tropical milkweed, Asclepias curassavica, which unlike the native milkweeds does not die back to the root in the fall. Oe spores can remain viable on the leaves of this perennial species for some time, infecting the next generation of caterpillars that eats them. As this situation repeats, it can cause populations of severely infested monarchs. We therefore encourage butterfly gardeners to cut back their tropical milkweed every spring after the first generation of monarchs arrive and eat the milkweed down, and then again in the fall before or during the migration, so that the butterflies will be encouraged to migrate and not overwinter here.
With all of these challenges, it’s no wonder that only five to ten percent of monarch eggs make it to adulthood. Keep in mind however, that monarchs are an important part of the food chain and without their survival and natural demise, our native ecosystem would not be as diverse as it is. In any case, human interactions with the environment have caused the most damage to monarch populations – huge amounts of monarch habitat has been lost due to the expansion of agricultural land and use of Roundup Ready crops. Planting butterfly-friendly gardens, especially if they include milkweed, can help mitigate this loss of habitat.
You can do your part by attending our fall plant sale at the Houston Museum of Natural Science. Stock up on the nectar plants that monarchs need to fuel their migration as well as host plants for native butterflies.
The sale will be held on Saturday, October 11th from 9:00 a.m. until noon (or until plants are gone), and will take place on the 7th level of the museum parking garage. Remember, the early bird gets the larva, so to speak, and don’t forget your wagon!
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.
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.
If 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.
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.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.
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.
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!