Wasps on Grand Mesa

Traveling along Interstate 70 in western Colorado, Grand Mesa rises as a magnificent tableland to the south of Grand Junction. It is unavoidable to even the most indifferent traveler - not because of its height, but because of its heft. One notices its horizontal profile - not an obvious trait of many other peaks in Colorado. And it is framed by a vast western sky. Panorama mixes with montane grandeur as a compromise between elevation and expanse. 

The interstate corridor of Colorado is one of the most awe-inspiring drives in the country. Timberline is visible all around, above an endless forest of spruce, fir, and pine. Clear white-water rapids filled with melting winter snow rush through sheer canyons. The experience goes on for hours and feels something like vertigo, but in reverse. The head gets dizzy from looking at the canopied heights.  

But by the time you get to Grand Junction, the topography is beginning to hint of western deserts. Now the many mountain peaks top out below tree line and are often without snow. The wandering gaze is pulled inexorably to the south and the green mass of Grand Mesa. 

Many mountaineers judge a mountain by its peaks. I certainly understand this pretension. Looking at a looming cliff or alpine summit, I can’t help but wonder if a 60-year-old man might find a route to the top with just a walking stick and a healthy amount of grit. But I am also a biologist with a history of looking closely at small animals - especially insects. And even though Grand Mesa doesn’t fill the true alpinist with dreams (after all, it doesn’t get much higher than 11,000 feet, which to a Coloradan is hardly worth mentioning) it certainly awakens the imagination of an entomologist who likes to climb mountains. 

Part of the appeal is that Grand Mesa is one of the largest flat-topped mountains in the world, with over 300 lakes and ponds, most of which occur above 8,000 feet. Fish in these waters have plenty to eat, and fishing boats abound as soon as the lakes are free of ice. But because the lakes are typically small, large boats, water skies, and other noisy vehicles are missing - at least much of the time. An entomologist can go quietly about his day looking for insects.

Dragonflies and damselflies flit about the margins looking for mates and picking off emerging mayflies and gnats - fueling their aerobic figure-eight nuptials. Females then touch their slender abdomena lightly over the surface, dropping one egg at a time into the cold water like a fairy queen wanding her minions. The cool mountain air washes over the summer traveler as both nepenthe and need. 

I woke up early and shook the drizzling puddles from my tarp. The western sky was turning coral. Syrphid flies started repositioning themselves on the honeysuckle leaves, eager for the sun to lift them back to life. There is much to see when looking for insects during the warming of a mountain day. 

I found the northern paper wasp (Polistes fuscatus) covered in dew on top of hemlock flowers - caring, not at all, that insect-eating birds had already begun to feed. Most of these birds have learned to leave these brightly colored and stinging insects alone. They are black with thin yellow bands and noticeably different from their saffron-colored congeners lower down. At 9,000 feet, they are darker, and more affined with their northern cousins. They seem somehow less menacing. I summon the nerve to pet one large female on her fuzzy thorax and wish her a happy day. 

It isn’t often that I get the chance to be so bold. But it is obvious from the chilly air and the open flowers that the wasps are not ready to be aggressive. They are still half asleep. I also take the opportunity to touch the wasp for another reason: Polistes fuscatus (this wasp species) is known to recognize faces. I don’t mean that they will ever recognize my face (although I smile half believing that this possibility does exist). But a fascinating study conducted two decades ago by Elizabeth Tibbetts at Cornell University showed that northern paper wasps do, in fact, recognize their sisters. 

Tibbetts noticed quite a bit of variability in the yellow markings on their faces (and abdomena). Other parts of the body had more regularly colored patterns. The variability suggested that wasps might be able to recognize individuals based on these patterns just like humans recognize individual faces by differences in facial features. 

Risking a number of unwanted stings, Tibbetts went out with her research team and collected 259 adult wasps from under the eaves of houses and barns in the Ithaca (New York) area. They then painted delicate yellow markings to some of the wasp faces, and obscured some of the existing yellow markings with black paint in others. Other wasps were painted on parts of the body other than the head. Then all of the wasps were returned to their colonies. 

What the researchers found was that the wasps that had their faces altered were not recognized by their nestmates. When they returned to the nests, they were attacked and otherwise harassed until the other wasps eventually came to acknowledge their identity. The wasps that were painted in non-facial regions did not receive the same aggressive treatment. 

These findings help explain one of the problems with paper wasp taxonomy: I mean the difficulty in defining species. In 1940 Joseph Bequaert at Harvard University published a study of paper wasps where he looked at thousands of specimens from across the country and decided that there were only four species. This came as a bit of a surprise because there had been many more names proposed in the literature. Entomologists, seeing the variability in color patterns, had recognized a number of species - quite a few more than just four. 

Bequaert recognized that there were a lot of color patterns within the four defined species but that these patterns did not justify the creation of new names. Taxonomic “splitters” before and after Bequaert’s time have insisted otherwise. And the uncertainty remains. Today we recognize more than four species. But the reason for the variability is becoming clearer. The color patterns are likely due to the fact that these wasps are social animals and the variability helps them recognize each other individually. They seem to be quite a bit smarter than we used to think.

Unfortunately our native paper wasps are struggling in many places all across the country because of an Old World species that arrived on the east coast in the late 1970’s. The invading species is the European paper wasp (Polistes dominula). It is affecting many of our native species in a number of different ways, but the one species that seems to be struggling the most is the northern paper wasp, including my new friend up here on Grand Mesa.

The two species don’t seem to be hostile to each other even though their ranges overlap in many parts of the country. But the European invader is four to five times more “productive” than the northern paper wasp (Gamboa et al., 2002). I place the word productive in parentheses because it is a suspect word. It is used in the literature to mean that worker wasps are produced earlier than native wasps, that foraging rates are higher in the invasive species, and that queens have a higher rate of survivorship, etc. 

But the distinction needs to be made between this so-called productivity and the broader benefits of a species that is adapted to its native environment in less “productive” ways. For several centuries now (since the Protestant reformation and the industrial revolution) we have given ourselves license to invent and otherwise alter the world with no other justification than that our efforts represent progress (sensu ipsum). 

There are numerous similarities between this so-called human progress and the characteristics that make for a successful invasive species. The fact that the European paper wasp is more productive in this sense than our native species and is more “successful” in producing offspring only make it more of a problem here - more of a threat to the balance of local ecosystems. Productivity in this case - not unlike the human example - has become the primary means of unraveling ecosystems.

The European paper wasp has occupied nearly every state (in the United States) and province (in Canada) in just 40 years and the damage it is causing has not yet been fully assessed. In my own backyard, I have discovered six nests this year alone. I was able to destroy three of them without risk of being stung. The others will have to wait until winter because of their size and location. 

Fortunately, these troubling thoughts are only vaguely in the back of my mind up here at the top of Grand Mesa. I have not seen a single invasive wasp up here in the two days I have spent looking for insects. I have to admit that these wasps are not actively hunting even an hour after sunrise. Scientists seem to be right - many of our native species do appear to be less “productive.” 

Maybe part of the reason is that it is still chilly up at this elevation. But I can’t help but feel that the mountain itself prefers to remain a bit sleepy. The only ones pushing to get an early start seem to be the humans eager to catch non-native fish that have been introduced into artificial reservoirs. 

The first time I ventured into the lake country of Grand Mesa was an unforgettable experience - but not in a good way. It was during the heat of the summer back in the 1990’s, and my friend and I had driven from Salt Lake City (Utah) to the orchards around Hotchkiss (just southeast of Grand Mesa in Colorado). We were doing an experiment to see if we could control some of the pests of fruit trees that are common here with a seed extract from the neem tree. Our goal was to replace some of the harsh synthetic insecticides with an environmentally responsible alternative. 

And we didn’t want to spend money on a hotel so we had planned ahead to sleep under the stars somewhere on Grand Mesa. By early evening, we found ourselves tired from the work of the day but also refreshed by the cooler air of the high country. We found a pull-off, grabbed our packs, and started along a short trail. Then as we hiked, the mosquitoes began to gather around us. 

I noticed them first near my legs. Then the bolder ones cued into the carbon dioxide in my breath and I could hear the high-pitched buzzing around my head. We began swatting them with our hands and our hats. But in the end, The mosquitoes won. We had not come prepared for the endless clouds that followed us wherever we went. They nearly drove us crazy.

But now I am fully prepared. The many dozens of lakes and ponds up here are obviously a perfect place for a semi-aquatic insect like a mosquito - an insect, that is, that lives in the water when it is young and then on land and in the air as an adult. In fact the habitat is so obviously perfect for mosquitoes that I am a bit embarrassed by my lack of foresight all those years ago. 

This time I have a small head-size mosquito net, a baseball cap, a hoodie, and gloves. Many of my friends and colleagues apply thick amounts of repellent to their skin and clothes. I have a different method that obviates this sort of chemical bath. After setting up my cot, I first put on the baseball cap in its proper position with the visor over my eyes. This will become important as it keeps the mosquito net from touching my nose and giving the mosquitoes a point of entry to my skin. Then comes the hoodie (fully zipped up) with the hood itself covering up the baseball cap in the back. The long sleeves also protect my arms. Then I put on the gloves, making sure that my wrists are covered, and then place the mosquito net over my head, making sure that it doesn’t leave any exposed skin around my neck in front. 

Wrapped up in all of this, I lay down on the cot and completely relax. I can see and hear the mosquitoes all around and my instinct is to panic. I swat at the mosquitoes until I remember that I don’t have to. I am protected. I jokingly tell myself that this ought to be an induction activity (or some other form of psychological testing) for anyone truly wanting to make a career in public lands. Passing means that you can answer the following question affirmatively: can you fall asleep to the sound of buzzing mosquitoes?

As my body slowly adapts to the fact that these mosquitoes can’t hurt me, I am able to enjoy the night air and the milky way high overhead in the black sky - so bold and bright and far away from the hubris of artificial lights. Sleep comes more quickly than I want. But, then again, maybe that’s the way it is supposed to be up here on Grand Mesa. I am certainly less productive. I think I am also more at peace with the world.

References

Bequaert, Joseph C. 1940. An introductory study of Polistes in the United States and Canada with descriptions of some new North and South American forms (Hymenoptera; Vespidae). Journal of the New York Entomological Society 48(1), 1-31.

Gamboa, G. J., Greig, E. I., & Thom, M. C. (2002). The comparative biology of two sympatric paper wasps, the native Polistes fuscatus and the invasive Polistes dominulus (Hymenoptera, Vespidae). Insectes Sociaux, 49, 45-49.

Henderson, J. (1923). The Glacial Geology of Grand Mesa, Colorado. The Journal of Geology, 31(8), 676-678.

McCarraher, Eugene (2022). The enchantments of mammon: how capitalism became the religion of modernity. Belknap Press, Harvard University. 

Tibbetts, E. A. (2002). Visual signals of individual identity in the wasp Polistes fuscatus. Proceedings of the Royal Society of London. Series B: Biological Sciences, 269(1499), 1423-1428.

Harvester Ants and Horned Lizards

July threatened to leave our meadow hot, windy and in need of rain. The summer monsoons were delayed and the garden was asleep. Paper wasps were still zigzagging slowly through the tall clump grass looking for things to eat, but most everything else was waiting for a break from the heat. 

One morning I walked outside before the sun came up and found four bucks - all sporting nearly full racks - nibbling on my grapes and cherry trees. I was mad. They had been taking their fill of the garden all year, and although I didn’t mind their leftover scat, I didn’t appreciate how much they had taken from some of my young trees. A small crabapple, a newly transplanted cherry tree, and a young serviceberry were almost completely defoliated and were barely hanging on. 

Our yard is a magnet for deer. It doesn’t matter that I am surrounded by neighbors with traditional (I mean non-native) plants that they might eat. The deer know that there are many of their native favorites in our yard, and that these are mixed in with savory fruit trees that seem to add a tasty supplement to their typical diet. They are willing to walk several blocks through developed neighborhoods in order to get to our yard. And they remember the way. And, once they get here, they know where each of our tasty plants can be found. 

Kathy is always slightly amused when I storm into the house cursing the deer. “We have created a meadow of native plants to encourage wildlife,” she reminds me. “And deer happen to be wildlife!” This is certainly true. And even though I am an entomologist and spend most of my efforts working with insects. The deer are not invasive in any natural sense. I grit my teeth and vow to keep waking up early to chase them away. 

This time, as I shooed the interlopers out of the yard, I noticed that one of them stepped right on top of a harvester ant mound. I checked on it later that day. It was alive with ants in the act of repairing the damaged mound. They didn’t seem bothered by the heat, but the other four mounds in the yard remained quiet. It was too hot for them and they had closed their mounds, blocking the entrances and calling all foragers back inside.  

Then we got an hour of rain on the last day of July. It was the first significant rain of the summer, the kind that makes your nares instinctively flare with delight. We sat out on the deck watching the sun go down enjoying the golden light on the cottonwoods in a kind of midsummer aromatherapy.

The next day was August and the forecast was for rain showers off and on for five days in a row. I was thrilled and went outside to let the ants know. They, of course, didn’t need any announcement from me. Their mounds were fully open and they were busy scouring the meadow for seeds and expiring arthropods. It’s funny how a large pogo mound can seem completely vacant one day and teeming with activity the next. 

Not far away on a small berm near an aspen, I almost stepped on another creature that was very happy to see the ants again: one of the three horned lizards (Phrynosoma hernandesi) that I know live in our meadow. It was already fat before the ants closed their doors in July and it certainly didn’t look under-nourished now, but it had gone without its primary food (ants) long enough. 

I’m always impressed every time I see one of these reptiles milling around pogo mounds. Occasionally they position themselves right on the mound itself. But most of the time they wait by the side of a trail and snatch up ants as they march past. It's fascinating to watch because they make it look so easy. There is no running and pouncing on their prey. And they don’t extrude a long tongue like a chameleon. They just capture one ant at a time in a lightning fast thrust of the head. If an ant moves out of range, it doesn’t bother to chase after it. It just waits until another ant comes marching along the trail. 

This habit of remaining perfectly still with the occasional head thrust gives the horned lizard a virtual cloak of invisibility. Ants confront the world (and especially each other) via chemical signals. They have “taste buds” (scientists call them  chemoreceptors) all over their bodies. One of these chemical signals is a distress signal that warns other ants of danger. But horned lizards can usually feed for many minutes without eliciting a warning signal of any kind. They are just too fast and take the hapless ants without warning and engulf them completely in their mouths. It appears as if the ants never even notice as their sisters get picked off one by one. 

But it turns out that the lizards have more up their sleeves - or maybe it would be better to say that they have more in their stomachs. When they snatch up the ants, they don’t take time to chew them. They are grabbed and swallowed whole. Maybe this doesn't seem like a big deal. We swallow large chunks of food all the time and never give it a second thought (even though this is not really a good nor a safe practice). But pogos are not the typical food. They are listed in some studies as having the nastiest arthropod venom around. Patricia Schmidt et al. (1989) write that “their venom has the highest known lethality to mice.” You would think that the horned lizards might be a little more cautious. 

The surprise is that they don’t have to be cautious. They aren’t in any danger. Something in their blood protects them from even very high concentrations of venom. And their stomachs are also unusual. When the ants are swallowed, most of them are still alive and capable of stinging. But the ants contain a viscous mucus that mucks them up. Even if the ants do sting a lizard’s stomach, it is many times more protected from the venom than other reptiles. Schmidt’s study found them over a thousand times more protected than mice. 

It does happen that a horned lizard occasionally gets overwhelmed by ants. I have never seen this happen in Southern Utah where both the reptiles and the ants have lived together for millions of years and have worked out a symbiosis that works well. In other parts of the country, however, the situation is different. In Texas, the invasive red imported fire ant (Solenopsis invicta) has taken over many areas formerly occupied by native ant species. 

Twenty years ago, a couple of herpetologists noticed that the horned lizards in their research area were behaving unusually. If the reptiles disturbed the aggressive fire ants and remained still, as this is their typical response, the ants would attack. If a few of the ants crawled over their bodies and started stinging them they would only close their eyes and wait. They would only eat the ants if they happened to get close to the mouth. If 20 or more ants ended up attacking them, however, this changed. They sprinted away from the fire ant mound and buried themselves in the soil. First they would wiggle their tails and then lower the rest of their bodies until they were completely covered. A few seconds later, the ants would emerge above ground, leaving the horned lizards alone (Webb and Henke, 2003). Somehow, the horned lizards intuited enough math to know the number of ants (and their toxins) that would swamp the protective enzymes in their blood. 

Many ants (including pogos) demonstrate what scientists call sting autonomy. This is a practice seen in some social hymenoptera (like wasps, bees and ants) where individuals will sting a threatening animal for the protection of the colony even though it means death for the stinging individual. Not all of the hymenoptera that carry stingers die when they sting. The ones that do (like honeybees) have developed a stinger that gets stuck in the skin of the unlucky subject. I often hear students commenting on how bad this seems for the bees. Why haven’t they evolved stingers that don’t get embedded in the skin of the target animal - like wasps, for example? 

In fact the barbed stingers - and the death that follows to the bees - are part of the reason for the success of this kind of sting. By leaving the stinger and the venom sack stuck in the victim after the adult bee has been swatted away, the pain of the venom is able to act more quickly and be delivered in greater quantity, thus reinforcing the warning to leave the bees, their home, and all that sweet honey alone (Schmidt, 2016). 

We usually talk about the sting autonomy of honeybees but harvester ants are also known to sting this way, even though it isn’t a human that they typically sting. If a human happens to walk inadvertently on a pogo mound, she will likely feel the ants crawling on her legs before getting stung - and have time to brush them off. This is not always the case with other predators. 

But horned lizards are rarely (if ever) attacked by native ants - not even harvester ants. I have never seen it happen, nor have I read any accounts of it happening. They aren’t agile enough to grab ants that might be crawling over their body. But they can run away and are quite fast if the need arises. And if they do get stung a few times, it doesn’t seem to bother them at all - at least that’s how it appears to humans that are not experiencing the stings themselves. 

These handful of adaptations for eating ants are shared by a disparate group of animals known as myrmecophages. Myrmecophagy is the technical term for ant-eating. Some spiders are myrmecophagous. Vertebrates like pangolins, echidnas, numbats, ant-eaters and some woodpeckers are obvious examples as well. The acorn woodpecker is even named for the practice (Melanerpes formicivorus). In the tropics there are a number of species of ant wrens and ant-pittas that are also specialists. Some species of frogs should also be added to the list. But these are exceptions. Ants are not part of most animals’ diets. 

The reason seems clear enough, it can be painful. And it requires several adaptations that most animals have never evolved. The ant-eating guild of vertebrates tend to have strong forearms and a stout claw for ripping into ant mounds. The teeth of many species have been reduced, or lost entirely, and a long tongue and a narrow mouth cavity have taken their place. The commitment to feed on ants is typically not a casual evolutionary development. Generalist predators tend to leave ants alone because of the grief they inflict. 

The myrmecophages have had to evolve solutions to the various ant problems. Their salivary glands are usually expanded and full of enzymes to break down the outer covering of the ants. This covering is called a cuticle and can be hard and difficult to digest. The salivary glands also contain enzymes for breaking down formic acid and other nasty chemicals in the ants’ bodies. 

Further along the digestive tract, many myrmecophages have a fortified (sometimes called a cornified) stomach. It is thick and can be stung much more often than the stomachs of other predators without causing serious damage. Once the ants make it to the small intestines, special enzymes actively begin breaking down trehalose, the distinct blood sugar found in ants and many other kinds of insects.

Some amphibians have become myrmecophages with the ability of separating the nasty chemicals within an ants body and moving them to their skin. The poison dart frogs of the Americas (of the family Dendrobatidae) are an example of this. We used to assume that the frogs made their own deadly skin toxins. We now know that most of these compounds are derived from the things that they eat. Plant alkaloids can be converted to toxins but also many insects end up being the source. Large tropical ladybird beetles with their orange blood provide some of these compounds. Millipedes do as well. But the majority of these toxins come from ants (Saporito et al., 2004). 

I wonder if the horned toads of the American Southwest might not have similar capabilities. Are they protected from other predators because they taste bad? Two scientists (Sherbrooke and Middendorf) conducted an experiment in 2004 that seemed to suggest this. Kit foxes that were sprayed with blood from the eyes of horned lizards tended to avoid eating the lizards as prey. After such an encounter, the foxes shook their heads from side to side as if trying to mollify whatever nastiness happened to be in the blood. The two scientists then coated mice with the horned lizard blood and watched as the foxes behaved in the very same way. It seems reasonable that the lizards are able to create such foul blood because of the ants that they eat. Clearly they have stumbled onto an evolutionary strategy that works well. And in fact horned lizards can be common throughout the American Southwest in places where ancient habitats still prevail.

Unfortunately, not all horned lizards are as happy as the ones in our small desert meadow. They don’t survive when cattle are allowed to trample on their homes. In many places of the West, harvester ants and cattle do co-exist. The ants seem to manage getting stepped on. Their rate of reproduction is more than fast enough to make up the losses. But the horned lizards are not. There is also evidence that pesticides take their toll. This sort of misfortune is happening all over the world. Animals and plants with remarkable adaptations to survive are not able to handle the new toxins and invasions of the modern world. 

Ant-eating animals are having to deal with these changes repeatedly. The example of horned lizards in Texas with fire ants is just one example. But what is the larger cost suffered by the lizards? How often can they be attacked by fire ants before they run out of defensive enzymes, or simply run out of energy by running away and burying themselves? 

I noticed many years ago that my own body is often confronted with this kind of tug-o-war. I don’t mean that I regularly get attacked by fire ants (although this did happen once by a beautiful stream in Louisiana). But I do often feel strong and even well adapted to certain environmental situations (like hiking, swimming in a cold lake, or even just weeding the garden) only to be stymied by an unlucky meal of industrial food. Sometimes a bad air day can keep me inside feeling lousy as well. 

How are we to deal with these problems? Harvester ants close up their mounds and wait for hard times to pass. They have proven (so far) to be resilient to the onslaughts of modernity. Horned lizards, not so much. As a result they are disappearing from many places where they used to be common. We humans seem to be proliferating successfully like ants, even as we as individuals and cultures are struggling to deal with a changing world. How long can we survive the industrial equivalents of fire ants? Maybe there is a lesson here in my own backyard. 

References

Camargo, A., & Maneyro, R. (2007). Environmental and seasonal variation in the diet of Elachistocleis bicolor (Guérin-Méneville 1838)(Anura: Microhylidae) from Northern Uruguay. Zoological Science 24, 225-231.

Cheng, S. C., Liu, C. B., Yao, X. Q., Hu, J. Y., Yin, T. T., Lim, B. K., ... & Yu, L. (2023). Hologenomic insights into mammalian adaptations to myrmecophagy. National Science Review, 10(4), nwac174.

Saporito, R. A., Garraffo, H. M., Donnelly, M. A., Edwards, A. L., Longino, J. T., & Daly, J. W. (2004). Formicine ants: an arthropod source for the pumiliotoxin alkaloids of dendrobatid poison frogs. Proceedings of the National Academy of Sciences, 101(21), 8045-8050.

Schmidt, J.O. (2016). The sting of the wild, the story of the man who got stung for science. John Hopkins University Press, Baltimore. 

Schmidt, P. J., Sherbrooke, W. C., & Schmidt, J. O. (1989). The detoxification of ant (Pogonomyrmex) venom by a blood factor in horned lizards (Phrynosoma). Copeia, 603-607.

Sherbrooke, W. C., & Middendorf III, G. A. (2004). Responses of kit foxes (Vulpes macrotis) to antipredator blood-squirting and blood of Texas horned lizards (Phrynosoma cornutum). Copeia, 2004(3), 652-658.

Webb, S. L., & Henke, S. E. (2003). Defensive strategies of Texas horned lizards (Phrynosoma cornutum) against red imported fire ants. Herpetological Review, 34(4), 327.