About Nancy

Nancy is Director of the Cockrell Butterfly Center and curator of entomology. A plant ecologist by training, she specializes in the interaction between insects, especially butterflies, and plants. The tropics are her favorite habitat, and she heads south to Central and South America whenever possible.

Visit Savage Garden for a glimpse at some of nature’s nastiest plants

In case you thought plants were not much more alive than a rock, think again! As David Attenborough pointed out in his wonderful series, The Private Life of Plants, plants have many behaviors as complex and interesting as those of animals. The problem is, plants move much more slowly, making their behaviors and reactions harder for us to appreciate.

During the month of October, the Cockrell Butterfly Center is celebrating Halloween with Savage Garden, bringing attention to some interesting things plants do. If you visit during that time, be sure to check out the map at the entrance and look for the purple signs scattered throughout the main floor of the rainforest.


You’ll be introduced to plants much older than the dinosaurs (Ancient Plants),


plants that protect themselves with spines, thorns, and prickles (Spiky Plants),


plants that defend themselves chemically (Delicious, or Deadly?), plants that heal us (Medicinal Plants), plants that use ants as bodyguards (Ant Plants),


plants that eat insects (Carnivorous Plants),

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plants that come back from the dead (Resurrection Plants),


plants with really putrid flowers (Stinky Plants),


and last but not least, a Miracle Berry plant (False Sugar). 

This is only a small slice of the interesting things plants can do. They have all sorts of adaptations to make more of themselves (via pollination and seed dispersal) and to move from one place to another (seed dispersal and crawling vines, etc.). Some of them can travel through time, with seeds that remain dormant for dozens or even hundreds of years. The protective chemicals of some toxic plants don’t necessarily have to be eaten, either – think about poison ivy. Urushiol (the chemical that causes the extremely uncomfortable blisters in some of us) is a powerful deterrant to humans. Yet birds gobble poison ivy berries with no ill effect!

Even stranger than the above behaviors is the discovery of inter-plant communication. Ecologists have known for a while that plants can “tell” other nearby plants of the same species that they are being attacked by insects via airborne chemicals, and the “listening” plants can then beef up their own chemical defenses. But according to recent studies, plants have other means of communication, some using underground networks of mycorrhizal (fungal) connections that network plants of many different species, and others apparently even making sounds! Check out this interesting article on “Plant Talk” by Dan Cossins in The Scientist

We don’t have any of these “talking” plants (that we know of) in the Butterfly Center, but please visit us in October to learn more about some of the other totally wicked things plants do in Savage Garden! #ChillsAtHMNS

Ants in your Plants: Mutualism benefits both myrmecophyte and insect

What is an “ant plant”? Because we are striving to portray a “real” tropical rainforest, we have several and plants at the Cockrell Butterfly Center, but what makes them so special? Technically called myrmecophytes (from the Greek myrmeco – “ant”, and phyte – “plant”), these plants have a very special relationship with ants, one that is beneficial to both parties. Such mutually beneficial partnerships are known as symbioses or mutualisms, and they are fascinating to evolutionary biologists, ecologists, and lay people alike. So-called “ant plants” typically provide shelter, and sometimes food as well, for ants, and the ants taking advantage of these resources in turn defend the plant against herbivores or other threatening animals, and sometimes even against competing plants. In some cases the ants may provide their host plant with nutrients.


Ants take shelter inside the passages within the swollen stem of this  Hyndophytum formicarum.

Examples of ant plants abound, particularly in the tropics. They occur in many different families of plants, and involve many different species of ant. Some plant-ant combinations are specific – i.e., the plant has co-evolved with a specific species of ant. In such cases this ant is usually found nowhere else: it has an obligate mutualism with its plant host.  Often the plant has difficulty surviving on its own as well.

More common are facultative mutualisms, where plants provide a resource (usually food) that a variety of ant species may visit. Simply by virtue of their presence on the plant, these ants discourage (or attack) herbivores or other organisms that might harm the plant.

Hundreds of plants bear extrafloral nectaries. These nectar-secreting glands on structures outside of the flower (usually on leaves or the petioles of leaves) are typically most active on new growth, which most needs defense against hungry herbivores. Ants gather at the nectaries to collect the sugary fluid they exude, and kill or chase off insects that try to eat the leaf.

extrafloral nectaries

Ants taking nutrition from extrafloral nectaries on an Inga leaf.

Less common, but still with plenty of examples especially in tropical areas, are plants that provide shelter for ants. These domatia may be hollow stems, swollen petioles, or other hollow spaces on the plant that ants can use as living space.

A few neotropical shrubs in the large genus Piper (black pepper family) have evolved large, envelope-like petioles that house a species of Pheidole ant. Tiny pearl bodies (lipid-containing food bodies) are produced on the inside surface of these domatia – at least when the ants are present. These tiny ants are not aggressive and would not seem to be very effective defenders of their host; however, they have been observed removing insect eggs and small larvae. The real benefit to the host plant appears to be the extra nitrogen that the plants absorb from waste (feces, dead bodies, and other debris) left by the ants inside the petioles.


Ants taking shelter within the domatia of a Miconia petiole.

Two shrubs in the coffee family, Hydnophytum and Myrmecodia, have very large and complicated domatia. The stems of these epiphytes from the mangrove forests of tropical Southeast Asia and Australia are lumpy and swollen, and almost look diseased. These bizarre-looking structures are riddled on the inside with hollow chambers, much like a Swiss cheese.  If you cut one of the tubers in half, you will find that some of the chambers have smooth surfaces, while others have darker, rough surfaces. The inhabiting ants use the smooth chambers for living space and the rough chambers for dumping their trash. Biologists have observed that the rough-walled chambers are able to absorb nitrogen and other nutrients from the decomposing wastes deposited in them by the ants, while the smooth-walled chambers are not absorbent. Since it is always a challenge for plants without roots in the ground to get enough nutrients high up in the treetops, this is a great adaptation to enhance these epiphytes’ survival. And, not only do the ants provide the plant with extra nutrition – their presence serves to deter things that might eat it.

ant acacia

Enlarged and swollen stipules on an ant acacia offer shelter for a colony of Pseudomyrmex, an ant species found nowhere else but this plant.

The ant-plant mutualisms that really capture our imagination are those obligate mutualisms where the plant provides both food and shelter for the ants, and the ants are particularly fierce defenders of their plant host.  One of the most famous ant-plants is the bull-thorn acacia from the dry forests of Central America. Acacia is a very large genus of plants in the legume family, especially abundant in dry tropical areas of the world. All Acacia species are characterized by having their paired stipules (little flaps of tissue at the base of each leaf, found throughout the legume family) modified into spines or thorns. In the Acacia species associated with ants, these thorns have become very large and swollen, resembling a pair of bull’s horns. A specific species of stinging ants in the genus Pseudomyrmex has evolved as an obligate mutualist of these acacias.  Worker ants make a small hole at the tip of one of the horns, hollowing out an interior, and the colony lives inside these chambers. These ants are found nowhere else.

The bull-thorn acacia also provides its ant inhabitants with food. Like many legumes, acacias have extrafloral nectaries. In this case, they take the form of little slits along the main rachis of the compound leaf. Ant-acacias don’t just feed their ants sugar, however; they also produce small, protein-rich food bodies for the ants on the tips of the new leaflets. The ants thus have all their needs for shelter and food provided by their host plant. In return, the ants vigorously defend their home against anything that threatens it – leaf-feeding insects or other animals – swarming out of the thorns and stinging the intruder. Because these ants also bite and sting any plant that touches or grows too close to their home, they reduce competition to their host from other plants as well, and because tropical dry forests often burn, the vegetation-free circles around the ant-acacia may be particularly important as a fire brake.  Evidence for how much bull-thorn acacias rely on their fierce little ant defenders can be discerned by tasting the leaves. While most Acacia species are full of bitter compounds, ant-acacias have little need to maintain these chemical defenses, and no longer produce them. Their leaves are not bitter. But if the ant-acacia should lose its ant colony, it is liable to be hit hard by hungry herbivores.


A species of Azteca ants takes shelter inside the hollow stems of Cecropia plants like this one.

The famous British naturalist Thomas Belt first described this amazing symbiosis, which he observed during his sojourn in Nicaragua in the mid 1800s. Today the food bodies borne at the tips of the new leaflets are called “Beltian bodies” in his honor.

A similar scenario, also from from the Neotropics, is seen in the relationship between several species of Cecropia (a fast-growing, early successional tree) and a species of Azteca ants. Cecropia has hollow stems – with special thin skinned “dimples” in the stem opposite each leaf.  A queen Azteca who finds a young Cecropia not yet colonized bores her way through this thin spot (called a prostoma).  The eggs she lays inside the stem hatch into worker ants, who tunnel through the membranes that divide the stem at each node, and open up more of the prostomata, giving them access to the outside. As the tree grows, the colony moves upwards, eventually making the whole tree a long, hollow shelter for the colony. Cecropia trees also provide food bodies for the ants; these “Mullerian bodies” (named for another 18th century European biologist, Fritz Muller) are produced on special spongy structures at the base of each leaf petiole. The occupying ants also bring small homopterans (aphid relatives) inside the stems of the Cecropia, where they feed on the plant’s sap in a protected environment.  The ants milk these small insects for their sugary exudate (called honeydew) just like farmers milk cows. Azteca ants do not sting, but they can bite, and the workers swarm out in huge numbers to attack any animal that touches their plant.

hollow stem with ants

Cutting into a hollow stem shows just how extensive the ant colony runs inside this plant.

A relationship very similar to the New World Cecropia-Azteca mutualism is found in the Old World tree Macaranga, also an early successional species, but in the spurge family, a completely different plant family from Cecropia. The ants inhabiting these plants are members of the ant genus Crematogaster (unrelated to Azteca). This is a great example of what is called convergence in evolutionary terms, whereby similar situations in different locations give rise to the same adaptive solutions among unrelated organisms.

Ants are amazing little creatures, and their complicated social behaviors, which often seem to mimic ours, make them particularly good partners for plants in the fight for survival.

Look for the bull-thorn Acacia (sans ants, unfortunately) next time you visit the Cockrell Butterfly Center. We recently received a specimen of Hydnophytum and of Mymecodia from a generous donor. These will eventually be placed in the rainforest. Our Cecropia tree, alas, got too big and died a few years ago. We hope one day to replace it!


Cold Snap Raises Concern: How will the monarchs fare?

Should I be concerned about the monarch butterfly?

Is it going extinct?

Will these cold temperatures kill the ones I’m raising?

What is “OE” and should I worry about it?

If you have questions about monarchs, you are in good company.

Thanks to the recent petition to US Fish and Wildlife by a number of conservation organizations to grant them “threatened” status, monarch butterflies have been in the news a lot this fall. Also, more and more people are hearing about the protozoan parasite that affects monarch health, the dreaded OE (short for the unpronounceable and unspellable “Ophryocystis elektroscirrha”). Finally, if you are in Houston, or other areas with monarch butterflies that do not migrate but spend the winter here, you may have questions about what this unusually early and unusually cold snap will have on the caterpillars and adults in your garden.

This is a quick response to all of those issues:

  1. Monarch butterflies are not in any sense endangered. The species is very widespread, found throughout the world, from Australia to southern Spain, Hawaii, etc., etc. What the groups petitioning for threatened status hope to achieve is to bring awareness to the possible end of the huge annual migration that takes place in the North American populations. Within the past decade or so, the number of individuals making the southern migration to overwintering grounds in Mexico has declined by about 90%. This is indeed worrying, and it would be a terrible loss if this unique and spectacular phenomenon ended. But there will still be monarchs – just not as many (millions instead of billions) and perhaps only non-migratory ones in areas where they can survive year-round. The decline in the North America population is thought to be due to a number of factors – the main one being loss of habitat. Genetically modified corn and soy beans have been bred to resist herbicides such as RoundUp, so farmers can spray their croplands for weeds (including milkweeds) and not affect these GMO crops. Until the widespread use of GMO crops, milkweed was abundant in the rows between plantings and in the highway right of ways.  Thus the huge expanse of farmland in the central USA cornbelt was critical in building up their populations during the breeding season (summer).  GMO crops, and subsidies for ethanol (which encourage corn farmers to plant every bit of their land, right up to the roadways) mean that this “cradle” of monarch populations is no longer available. There are other factors causing the huge decline in the migratory population – global climate change, urbanization, some habitat loss in Mexico – but this, i.e., habitat loss in the central USA, is the main factor. We do not know yet whether monarchs will be designated as “threatened” – such proposals take a long time to go through the various review processes. The good news is that this petition is raising awareness about this worrying loss of habitat – which affects not only monarchs, but bees, other butterflies, and many other organisms.

  1. “OE” is a naturally occurring protozoan parasite of monarch and queen butterflies (genus Danaus). This tiny organism multiplies inside the caterpillar stage, and is spread in a dormant spore form by the adult butterfly. Low levels of OE do not greatly affect their hosts, but parasite levels build up rapidly over successive generations of monarchs, and when infection levels are high, many detrimental effects (including death) are seen. Infected caterpillars may not pupate properly, or they may not be able to get out of the pupa, or the adults may be weak, malformed, or die early. Unfortunately, well-intentioned people raising successive generations of monarchs, especially on tropical milkweed (which does not have an annual dormant period) appear to be the main cause of OE buildup (via the very persistent spores).

    In areas like Houston, where mild temperatures allow for resident, non-migratory populations year-round, researchers have found that most adult butterflies are carrying the spores (i.e., over 75% of the butterflies they test are infected). For more information, visit the Monarch Watch organization’s website or click here for more information from the University of Georgia.

    You can also find plenty of information by doing an online search for Ophryocystis elektroscirrha.

  1. You raise monarchs and are concerned about whether they can survive the cold temperatures we’ve been having.

    The whole “point” of the monarch migration is to avoid cold temperatures – monarchs are really tropical butterflies that, like many songbirds, take advantage of our summers. However, in our area where it seldom gets truly cold, and where there is now lots of tropical milkweed available, thanks to the butterfly gardening craze, some monarchs forego the migration and spend the winter here, where they continue to breed (the migrating monarchs do not mate or lay eggs until spring). 

    Cold enough temperatures can certainly kill or harm monarchs, especially in the caterpillar stage or if they are in the process of pupating. However, unless it freezes and/or the caterpillars, pupae, or butterflies are highly exposed, monarchs can survive temperatures in the 30s. 

    During a cold snap, caterpillars will often crawl to the base of the milkweed they are eating and curl up on the ground until it warms up again. Adult butterflies can hunker down in a sheltered area and will come out again when it’s warm enough to fly. But if it’s cold enough for long enough, they will die. Of course it’s hard to tell people to let nature take its course — but that is probably best — especially given the high levels of OE we see in most people’s home-grown monarchs. If you do want to save your babies, you can always bring them inside for a few days until it warms up. 

    Butterflies can be fed sugar water, Gatorade, or fruit juice (place them with their feet touching a sponge or paper towel moistened with one of these sweet fluids and they will probably extend their proboscis to get a meal. If you would like to test to see if your butterflies have OE (only the adults can be tested), click here to learn how to do it. We (at the Cockrell Butterfly Center) would be happy to look at your samples, or you can send them to the University of Georgia.

If you have questions that were not answered here, feel free to write us at bfly-questions@hmns.org.




Mean green flying machines: the hummingbirds are here!

Photo by JC Donaho. http://jcdonaho.com/

Photo by JC Donaho. http://jcdonaho.com/

What was that high pitched chirping and flash of iridescent green that just whizzed past at lightning speed? You just got buzzed by a hummingbird! The fall migration is passing through Houston, and these feisty little birds seem to be particularly abundant this year. Houston does not have (for the most part) any resident hummingbirds, but a few species pass through in spring and fall as they fly between their nesting grounds in the northern states and Canada, and their wintering ground in Central America.

The northward spring migration is much more diffuse than the fall event – you may hear a hummingbird or two in February or March, but they don’t linger. However, in late August through September and into early October, hummingbirds can be very evident in Houston. These marathon travellers will pass through our area for about 4 to 6 weeks, stocking up on fuel to take them over the Gulf of Mexico to their winter abode. They are particularly abundant on the Gulf Coast, where inclement weather can force them to stay put until a more opportune time comes to complete the migration. Rockport, Texas hosts a huge “Hummerbird Festival” every mid-September, with lots of talks on hummingbirds and other birds, butterflies, etc., and home tours to see gardens that are particularly full of hummingbirds. It’s over for this year, but put it on your calendar for future years and check it out!

Ruby-throated Hummingbird. Photo by JC Donaho http://jcdonaho.com/

Ruby-throated Hummingbird. Photo by JC Donaho http://jcdonaho.com/

Most hummers you see in Houston (and in Rockport) are Ruby-throated Hummingbirds. Males are a metallic green with white bellies, and are named for the patch of dark feathers on their throat that glows a brilliant, iridescent ruby red when the sun hits it just right. Females and immature males do not have the spectacular throat coloring, and are white underneath. Some young males may have a fleck or two of red on their throat.

Two other species are sometimes seen here – the Rufous Hummingbird and the Black-chinned Hummingbird. Juveniles and females of these species are a little hard to distinguish from Ruby-throated females and youngsters, but the males are distinctive. Rufous males are a bright bronze color, with an orangey red throat. Black-chinned males are green with a black throat, below which, in the right light, a brilliant violet band will flash.

Ruby-throated Hummingbird. Photo by JC Donaho http://jcdonaho.com/

Ruby-throated Hummingbird. Photo by JC Donaho http://jcdonaho.com/

Farther west, in the Big Bend area and west into New Mexico, Arizona, and California, hummingbird diversity is much higher. About 15 or so species are known from the USA, and most of these occur in the western states. For the apex of hummingbird diversity, head to the highlands of South America (e.g., Colombia, with about 140 species), where dozens of different species can be seen, some of them truly spectacular. Most of these are residents in the tropics and do not migrate.


Male and Female Ruby-Throated Hummingbirds, slow motion, August 2010 from Hummer Lover on Vimeo.

All hummingbirds behave similarly. Masters of speedy, controlled flight, they can hover in place, move backwards and forwards, dive and soar with incredible speed and precision. They can reach speeds of up to 60 mph, their wings whirring at 80 beats per second. Males in particular are territorial and aggressive, cheeping furiously as they drive off rivals from a good food source.

Ruby-throated Hummingbird. Photo by JC Donaho http://jcdonaho.com/

Ruby-throated Hummingbird. Photo by JC Donaho http://jcdonaho.com/

Hummingbirds’ main food is flower nectar, so they are important pollinators of certain species of plants. They especially seem to gravitate to red flowers, although other colors are visited. Their long thin beaks and even longer tongues allow them to reach inside floral tubes that are much too deep for most butterflies and bees. Since birds in general have a poorly developed sense of smell, flowers pollinated by hummingbirds typically have no scent.

Hummingbirds also eat small insects such as fruit flies and gnats, catching them on the wing or finding them inside the flowers they probe for nectar.

Bottle feeder with ant-guard

Bottle feeder with ant-guard

Because they love sweet fluids, it is easy to provide feeders for hummingbirds, and several designs are available. Hummingbird food is simple to make; you just need sugar and clean water. DO NOT use any other sweetener – including honey or other types of sugar –just your standard white table sugar. Use four parts water to one part sugar. Bring the water to a rolling boil, add in sugar and stir until it dissolves, then turn off the heat. Do not cook it too long or it will start to caramelize. Let the solution cool and you are ready to fill your feeders. Keep extra sugar solution in the refrigerator.

IMPORTANT! If you want to feed hummingbirds you must commit to regularly changing their sugar water food! Sugar water ferments and/or grows mold quickly, and when spoiled it can make hummingbirds sick. Since you will need to clean the feeders about every three days, do not fill them too full or you will waste a lot of sugar solution. Fill them from between ¼ to ½ full, at least until you see how fast the hummers empty them.

DO NOT add red food coloring, and avoid commercial solutions with food coloring. Coloring is not necessary, as most feeders have red parts built in to attract the hummers’ attention. Like spoiled sugar water, food coloring is bad for the hummingbirds’ health.

Every three days, even if your feeders are not empty, clean them thoroughly with hot water and refill them with fresh solution. At the end of the season you should sterilize the feeders either in the dishwasher or using a dilute bleach solution before drying and storing them until next year. I prefer to use glass feeders as these are easier to sterilize.


Perky Pet feeder

Perky Pet feeder

A few guidelines on feeder placement – hummingbirds are not at all shy, so you can put feeders near your house where you can enjoy watching their activity. I put one right outside my kitchen window, and hang others around my back yard, especially near trees or bushes where hummingbirds can perch between bouts at the feeder. If you put out more than one feeder (I recommend this!), don’t put them too close, and ideally place them out of sight of each other to avoid their being monopolized by one dominant male.

Salvia leucantha, aka Mexican Sage

Salvia leucantha, aka Mexican Sage

In a good season, you will have dozens of hummingbirds – and the more feeders, the more hummingbirds! I usually put out from 3 to 9 feeders, depending on activity. Of course, hummingbirds also visit flowers for nectar. The classic hummingbird flower is red with a long floral tube, but many others also bring them in. Some good choices are salvias (many varieties), hummingbird bush, coral vine, trumpet creeper, and russelia.

Salvia guaranitica, or Purple Majesty Sage

Salvia guaranitica, or Purple Majesty Sage

Of course, if you have outdoor cats, you should not put out hummingbird feeders or any other kind of bird feeder!

Did you know?

  • Hummingbirds are only found in the Western Hemisphere.
  • Hummingbirds’ jewel-like, glittering colors do not come from pigments, but result from the refraction of light hitting special structures on their feathers.
  • The Bee Hummingbird from Cuba, less than 2.5 inches long, is the world’s smallest bird.
  • The largest hummingbird is the Giant Hummingbird, from Patagonia, Chile. It is about the size of a cardinal, but only weighs half as much (about .65 ounces, or about 1/20th of a pound).
  • The longest hummingbird is the Black-tailed Trainbearer from Colombia. The male’s total length is about 10 inches, including its 6.5 inch tail!
  • The Sword-billed Hummingbird from Ecuador has a 4 inch long beak, almost as long as its body!
  • Check out the PBS Nature special on hummingbirds, “Magic in the Air,” for some amazing footage of these incredible creatures!