It Takes a Village ….A Milkweed Village

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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.

Ladybug larva

Ladybug larva

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).

scale destroyer larva2

Scale destroyer larvae

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.

Syphid fly pupa

Syrphid fly larva

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.

aphid mummy

Aphid mummies

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.

Milkweed Beetle (Wikipedia)

Milkweed Beetle (Wikipedia)

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.

monarch

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.

Tachinid fly larva emerging from monarch caterpillar.

Tachinid fly larva emerging from monarch caterpillar.

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.

Polistes carolina  Photo by Val Bugh

Polistes carolina Photo by Val Bugh

 

Polistes dominulus

Polistes dominulus

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.

OE Life Cycle (Monarchparasites.org)

OE Life Cycle (Monarchparasites.org)

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.

Spiny soldier bug nymph eating a monarch caterpillar. (Photo by Dan McBride)

Spiny soldier bug nymph eating a monarch caterpillar. (Photo by Dan McBride)

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!

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

Butterflies will blow your mind: A new Giant Screen Theatre film gives viewers new respect for migrating Monarchs

If you — like me — have long thought of butterflies as delicate, simple creatures, you have been sorely mistaken.

A new Giant Screen Theatre film, Flight of the Butterflies, opens tomorrow and frames familiar Monarch butterflies in a new light as masters of migration. The film follows the life’s work of Dr. Fred Urquhart and his wife in stunning 3D as they tag and track the migratory patterns of Monarch butterflies. After 40 years of tracking and thanks to the  help of thousands of citizen scientists, the Urquharts were finally able to unlock the mystery of Monarch migration and identify their winter gathering place in remote mountaintops of Mexico.

Flight of the ButterfliesAnd it’s not just the visual spectacle that’s stunning. Did you know that a super-butterfly is born every third generation that lives longer and flies farther than its predecessors? Or that this Super Generation that makes the extended trek from Canada all the way to Mexico can fly as much as mile up in the air, catching rides on the wind? It challenges your perception of butterflies as erratic, delicate things, that’s for sure. They’re marksmen; weathering one of the longest migrations on earth to target an isolated mountaintop they’ve never even seen with incredible accuracy. Even our great state of Texas is featured, in all its bluebonnet-blanketed glory.

Make it a butterfly-filled weekend with the Semi-Annual Plant Sale and you can even establish a garden to help these guys along! For a schedule of showings, click here.

Tagging Monarchs at HMNS

Today Soni (CBC horticulturist) came down to my office and said “You should see all the monarchs in the outdoor butterfly garden. They must be part of the fall migration. Why don’t we tag them?”’

Surely by now most people are aware of the amazing migration undertaken each year by the fall generation of monarch butterflies. As the temperatures cool and the days shorten, monarchs emerging from their chrysalids are cued to head south. Somehow they “know” that their survival depends on it. Before winter sets in, millions of individuals – basically the entire eastern population – start to fly southwest, towards the remote mountain sites in central Mexico where they will spend the winter hanging on the branches of fir and pine trees.

Soni and net
Soni netting butterflies

The spring and summer generations behave very differently. After emerging from its chrysalis, one of the first things a new butterfly typically does is look for a mate (“nature abhors a virgin” as my friend Phil DeVries would say). Mated females search for milkweed plants on which to deposit their eggs; males look for more females! These fair-weather generations probably live for a month or so as adults. The autumn generation, however, does not mate, but saves its energy for the long journey ahead. As fall approaches, butterflies stock up on nectar, packing on fat for the flight and for several months of hibernation.

At the northern edge of the population (southern Ontario/northern Great Lakes area), the migration starts in late August, with butterflies flying on average about 50 miles a day and picking up more migrants as they travel south. By early to mid October, monarchs are streaming through Texas. Virtually the entire eastern population passes through our state – but most of the migrating butterflies pass to the west of us, through Dallas and Austin and San Antonio, then over to Del Rio and into Mexico. Since fewer butterflies typically pass this way, the coastal migration route is not as well known. All the more reason for us to get out there and tag!

monarch tag
How to tag a monarch

Monarch researchers began tagging monarchs back in the early 70s, even before anyone knew where the migrating monarchs were ending up (the roost locations were discovered in 1975). Tagging data collected over the years has enabled us to map the distribution of the population, and to understand that a single generation makes the long trip south and then heads north again after spending the winter, largely dormant, in Mexico. This is hard for some people to understand, especially given that most butterflies only live for a few weeks. The migrating/hibernating monarchs may live as long as eight or nine months.

tag instructions
Tagging instructions from Monarch Watch

The monarchs’ arrival at the overwintering grounds typically coincides with Dia de los Muertos (November 1, Day of the Dead), an important fall festival in Mexico. Some locals apparently see the orange and black visitors as the spirits of their dear departed relatives, returning to celebrate the day. This is not as far-fetched as it may seem; throughout history humans have used butterflies as symbols of the soul and/or reincarnation. Did you know that the word “pysche” in ancient Greek meant both “butterfly” and “soul”?

But back to the present, and Houston. It was a beautiful afternoon so we all trooped outside, armed with nets, pens, data sheets, and numbered tags purchased in advance from Monarch Watch, a non-profit organization based at the University of Kansas that coordinates monitoring efforts. Soni also took a roll of scotch tape and some microscope slides. She is checking the butterflies for OE (short for Ophryocystis elektroscirrha), a sporozoan parasite. If present, the parasite spores can be seen under a compound microscope (they are much smaller than butterfly scales). If there are enough of them in a caterpillar’s body, these parasites can spell death for the butterfly. Luckily, parasite loads are typically low in migrating individuals – perhaps butterflies weakened by the parasites simply can’t make the long journey.

OEtest
Taking scale sample for OE test

Lots of monarchs were coming around the corner of the Butterfly Center, dipping down to our outdoor butterfly garden and stopping to sip nectar from the blooms (they especially seemed to like wheat celosia and purple porter weed). Then they’d head off towards the Sam Houston statue and on in the direction of Rice University (southwest of us!). We caught 11 butterflies in the garden (and missed many more), tagged them (noting whether male or female), took a scale sample, and released them. Off they flew!

We’ll send in our data to Monarch Watch, and of course we hope that someone will find one or more of our tagged butterflies on the roost in Mexico. It is highly unlikely – given the millions of monarchs at the roost – but tagged butterflies (usually dead ones) do get found and reported. If one of ours is found, Monarch Watch will contact us – and they/we will know that butterflies do migrate to Mexico from our area.

tag team
Tag team

Local butterfly gardeners know that a number of monarchs stay in Houston over the winter. We often don’t have killing freezes here, and the recent craze in butterfly gardening means that there is lots of Mexican Milkweed aka Butterfly Weed around.  This plant, Asclepias curassavica, is a perennial from Central America; unlike our native milkweeds, it does not die back in the winter months. Also, predatory wasps, which take many caterpillars during the summer, are mostly gone – so if it doesn’t get too cold, Houston is a good place for monarchs to spend the winter. However, these butterflies are taking the risk of dying should we have a strong cold snap as we did last year.

Here are two great websites with information about these amazing butterflies and about how to get involved monitoring their migration: Monarch Watch at www.monarchwatch.org and Journey North at www.learner.org/jnorth/.