It Takes a Village ….A Milkweed Village

monarch-2

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!

Finding the flora and fauna: Butterfly Center staff conduct a BioBlitz in Memorial Park

Editor’s Note: The term “BioBlitz” was first coined in 1996 for intense attempts to record all the flora and fauna within a designated area. National Geographic, which has partnered with parks around the country for various BioBlitzes, describes them as “a 24-hour event in which teams of volunteer scientists, families, students, teachers, and other community members work together to find and identify as many species of plants, animals, microbes, fungi, and other organisms as possible within a designated area.”  These quick and dirty surveys are used both to gather information about the biodiversity of a given area, and since members of the public and other non-experts (students, etc.) are often included as participants, as ways of sparking public interest in local flora and fauna.

The “Eco-Tech” panel of the Memorial Park Conservancy recently recruited the Butterfly Center to conduct a preliminary survey or “mini-BioBlitz” of the insect fauna throughout Memorial Park, with the idea of inviting members of the public to help on future surveys. One of the goals of the panel is to get some baseline data on the biodiversity of all the creatures that live in Memorial Park, and from there, make plans on how best to preserve and manage or enhance this wildlife.

We were asked to survey several different natural habitats in Memorial Park (i.e., not the golf course). On a sunny morning in early July, Butterfly Center staff members, our summer intern, and a couple of volunteers drove out to Memorial Park armed with insect nets and containers.  While some surveys (such as birds or trees) can be done without collecting, there are so many kinds of insects (and so few experts) that at least some specimens have to be collected in order to make identifications.  

We decided to sample 10 transects — 100 feet long by about 8 feet wide — each one in a different area. Our first couple of sites were in open prairie vegetation, so we used sweep nets and aerial nets to collect samples. In case you are not versed in insect collection techniques, a “sweep net” is a canvas net bag on a sturdy metal frame that is swished through the vegetation. Periodically, the contents are emptied into Ziploc bags or other containers. 

This giant fishing or nursery web spider was nearly three inches across! (photo by Zac Stayton)

This giant fishing or nursery web spider was nearly three inches across! (Photo by Zac Stayton)

 

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We found lots of these small millipedes (and a few slugs) in the leaf litter in the forested areas. (Photo by Zac Stayton)

Aerial nets are the more familiar “butterfly nets”: a much lighter, more delicate net bag that is swung through the air (it should NOT be dragged on the ground, used in water, or swiped through bushes!). These nets are more for catching fairly large, individual insects, especially ones that fly, so samples are put directly into a glassine envelope, or vial, or other appropriate container (or, if it is something readily identifiable, simply noted and released). Sweep nets generally collect things like grasshoppers and katydids, walkingsticks, mantids, leaf hoppers, stink bugs, the odd caterpillar, spiders, etc. Aerial nets are useful for larger flying insects such as butterflies, dragonflies and damselflies, wasps, bees, some beetles, certain flies, etc. 

In the more forested areas, sweep nets were not really appropriate, so we used the aerial nets and also took litter samples (scraping up leaf litter and bagging it). Litter samples are typically brought back to the lab to process in a so-called Berlese funnel. Many small arthropods who live in the litter of the forest floor, including springtails and cockroaches, ants, small beetles, millipedes, etc., can be collected in this way.

 Another find in the leaf litter:  a “woolly bear” caterpillar.  This is the larval form of the Giant Leopard moth, Ecpantheria scribonia.  The caterpillar rolls up in a ball, showing red stripes between segments covered with black “fur” (these caterpillars do not sting but probably taste bad so are warningly colored).  (photo by Nancy Greig)


A find in the leaf litter: a “woolly bear” caterpillar. This is the larval form of the giant leopard moth, Ecpantheria scribonia. The caterpillar rolls up in a ball, showing red stripes between segments covered with black “fur” (these caterpillars do not sting but probably taste bad so are warningly colored). (Photo by Nancy Greig)

There are many other collection techniques, none of which we used in this preliminary survey. Pitfall traps are always fun; they are empty cans or jars set into the ground with their mouths at ground level. Sometimes bait (a little raw chicken or fish, for example) is put in the bottom.

Crawling insects, especially those interested in odorous food, fall into the “pits” and cannot get out. Such traps need to be checked every couple of days — often they will contain different kinds of beetle, maybe a cockroach or two, etc.

Malaise traps are screen tents or baffles that trap small flying insects. The insects get caught in the folds of the screen and since they typically crawl upwards to escape, can be funneled into a container filled with alcohol.

Yellow pans are any wide, shallow container with a yellow (painted or otherwise) bottom.  These are partly filled with water and a bit of liquid detergent. Wasps and pollinating flies, etc., are attracted to the yellow color and cannot escape once they fall into the soapy water. Yellow pans need to be used in open areas in sunny weather and the samples removed every day or two.

Our final survey site was along the banks of Buffalo Bayou, which was much higher than usual so there was not much shore. Here, we mostly used aerial nets. We saw several things in this area that were not seen other places, especially tiger beetles, damselflies, etc. Here, we mostly used aerial nets (or grabbed things with our hands). 

The gorgeous Ebony Jewelwing a common damselfly species along the banks of Buffalo Bayou in Memorial Park

The gorgeous Ebony Jewelwing, a common damselfly species along the banks of Buffalo Bayou in Memorial Park.

 

The vibrantly colored Vivid Dancer is a common damselfly species along the banks of Buffalo Bayou in Memorial Park

The vibrantly colored Vivid Dancer is a common damselfly species along the banks of Buffalo Bayou in Memorial Park.

By noon, it was blazing hot and we were all soaked in sweat, so we bagged things up and stopped at the Shandy Café (great little place on Memorial Drive) for lunch on our way back to the Museum. 

Although we only collected for about three hours, we have our hands full in identifying everything. We first have to sort things to order, identify what we can, and then we will probably have to send some things off to experts in the various insect groups. I’m sure it will take us several weeks! 

Some of the coolest things we found: 

It’s always fun to open up the sweep net and find walkingsticks or praying mantids, or a colorful leafhopper. We picked up quite a few different grasshoppers and a few katydids.  We noted but did not catch too many butterflies (we can identify most of these by sight, so no need to collect).

I like wasps and bees; we saw several of the large red Polistes wasps, carpenter bees, leaf cutter bees, and a really cool “digger” bee starting her nest tunnel in the sand (see attached video clip). A medium-sized beetle that looked like a wasp was visiting flowers in several places. 

The very fast tiger beetles mostly eluded us down at the bayou’s edge, but we did catch a few damselflies there. The most common one there was the lovely Ebony Jewelwing.

Tiger beetles are extremely fast moving, long legged, predatory beetles that often occur in open sandy areas, especially along streams.  We saw many of these, probably Megacephala virginica – and managed to catch a few – along the bayou.  (photo from BugGuide.net by Chris Wirth)

Tiger beetles are extremely fast moving, long-legged, predatory beetles that often occur in open sandy areas, especially along streams. We saw many of these, probably Megacephala virginica – and managed to catch a few – along the bayou. (Photo from BugGuide.net by Chris Wirth)

 

Hibiscus bee, Ptilothrix bombiformis

Click here to watch a video of a female Hibiscus bee, Ptilothrix bombiformis, a solitary species as she digs a nesting tunnel into hard-packed earth as we found on our BioBlitz.

Once we have compiled our results and reported them to the EcoTech Panel, they will then make plans for another survey sometime in the fall. I believe they intend to invite more general participation, so if you are interested in the insects of our area, keep your ears open!

STEM & GEMS: Insects and plants fascinate “bug nerd” Lauren Williamson

lauren photo in CBCEditor’s Note: As part of our annual GEMS (Girls Exploring Math and Science) program we conduct interviews with women who have pursued careers in science, technology, engineering, or math. This week, we’re featuring Lauren Williamson, Entomologist in the Cockrell Butterfly Center

HMNS: How old were you when you first became interested in science?
Williamson: Ever since I can remember! I was always catching bugs, playing with animals, and looking at flowers, plants, etc.

HMNS: Was there a specific person or event that inspired you when you were younger?
Williamson: I had a biology teacher in junior high that told me about entomology and told me that I should look into that field for a career since I had such an interest in insects.

HMNS: What was your favorite science project when you were in school?
Williamson: An insect collection, of course!

HMNS: What is your current job? How does this relate to science, technology, engineering, or math?
Williamson: My title is “entomologist”, aka “bug nerd.” My job revolves around importing exotic butterflies to display in our Butterfly Center. Not only do I need to know a lot about insects, but I also need to know about government regulations, computer applications, and accounting. We also do a lot of outreach programs, so it’s a necessity to be comfortable presenting to large groups.

To get a degree in entomology you have to take extensive coursework in biology, chemistry, physiology, and math.

HMNS: What’s the best part of your job?
Williamson: I play with butterflies all day — need I say more? Not to say that my job doesn’t involve a lot of hard work, because it does, but the fun parts of my job make it all worth it!

HMNS: What do you like to do in your spare time?
Williamson: I love to play with my animals (three dogs: Merle, Hank, and Molly; and a bird: Carlos), go on insect collecting trips, camping, crafts, going to museums and seeing movies with my husband.

HMNS: What advice would you give to girls interested in pursuing a STEM career?
Williamson:
Make sure you study, study, study! Ask a lot of questions and learn all of the material as much as possible. Every year adds more information to the knowledge base you already have, so it only gets harder.

HMNS: Why do you think it’s important for girls to have access to an event like GEMS?
Williamson: This is a great way to experience some of the wonderful career paths you can take with a firm knowledge of science, engineering, technology, and math. These subjects are the foundation of our everyday lives, whether you realize it or not! There will always be a demand for employees in these ever-growing and changing fields so it is important to get in an interest in them as soon as possible.

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Tales from Tanzania: That’s no mint on your pillow

Some hotels leave mints on pillows. But in the African Serengeti, you get assassin bugs.

Assassin bug on a pillow

Not a mint.

Dave and I had been actively searching for invertebrates on our trip to no avail. The guides thought we were weird (crazy) from all of our questions about insects (as well as snakes and lizards). No one goes to Tanzania for the little things — they’re only interested in the big stuff.

So imagine our delight when we came “home” one night and discovered this AWESOME assassin bug on our pillows.

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David, with our non-mint, and our pillow.

Assassin bugs are awesome because they have specially adapted mouths, perfect for sucking “the goodie” out of other insects. They pierce through the exoskeleton of their prey and inject saliva into the body. The saliva liquefies the innards of the prey, which can then be sucked right out (like a smoothie!).

An assassin bug with its prey.

Not only are assassin bugs insect-smoothie-enthusiasts, but they’re great at defending themselves. They can spit their saliva into the eyes of those things that might try to eat it (birds) or accidentally disturb it (humans), causing temporary blindness.

Now tell me that’s not awesome.

The life cycle of an assassin bug

DISCLAIMER: We may have totally lied to everyone on the trip — and by, “We may have lied,” I mean, “We totally lied.” Knowing what the assassin bug can do, we decided to tell our fellow travelers that we found it outside our room rather than on the pillow. Why cause a panic? (But don’t tell the others.)

Kwa heri!