The scene: The Madrean Sky Islands, an archipelago of dozens of mountain ranges that unify the spirits of the Rockies and the Sierra Madre, the Sonoran and Chihuahuan Deserts. This is a land of astonishing diversity by almost any measure. The following story is based on a visit more than a decade ago to the Ash Canyon property of Noel McFarland in the SE part of the Huachucas, a range noted for abundant and varied birds, mammals, and reptiles.
But birds, mammals, and herps are not why I came to see Noel McFarland. He is a collector of diversity with a twist all his own. McFarland knows moths. I follow him through several rooms where he works. Noel collects more than moths, it seems, and twenty years’ accumulation of boxes, books, papers, and other memorabilia fills his spaces the way floral diversity fills a rainforest.
Butterfly aficionados have a number of guides they can use to help with identification. Watchers are proliferating. But McFarland avoids the lepidopteran crowds. His collection of butterflies is meager. There are two small boxes on a crowded shelf, almost lost in chaos; one is hand-labeled “skippers only” and the other says “misc. butts.” So much for butterflies here.
In contrast, there are beautiful collection boxes, big ones with wood frames and glass covers, devoted to hundreds of species of moths Noel has collected. There are no popular, broadly inclusive moth field guides, for visual impressions can be unreliable. Many species are similar, even when unrelated. Sexes can be strikingly different, and variation within a species can trick the devil out of you. Few moths have common names, so most hide behind Latin epithets often longer than their caterpillars.
Noel goes over each box with me, as enchanted by the beauty and diversity before us as I am, though he surely has looked at them hundreds of times. They are beautiful, some colorful, some gaudy, but each perfect in its own way. For many, he has discovered the larval host plant, often by testing alternative plants with captives. There is abundant life history information that, at present, only he knows. Diversity only partly is reflected by the naming.
If butterflies in SE Arizona are considered to be a diverse group with 240 species, then moths must be recognized as megadiverse. Already on these five acres, a pinprick on a map of Cochise County, he has collected and identified over 950 moth species. His property has more moth species than all the butterfly species in the United States.
And McFarland is still choosy about what he will collect. He only does the “Macros,” a subset of the order Lepidoptera. Actually, the usual distinctions between butterflies and moths are rather artificial. Both the butterflies and the types of moths he collects are part of the Macrolepidoptera; some other “moths” are in the Microlepidoptera, the “Micros.” As a rule of thumb, there are two Micros for every Macro, so if this relationship holds for the five-acre parcel, there easily could be a couple thousand species there. If there are perhaps three thousand species of moths just on McFarland’s place, how many species might reside in the entire Huachucas? In Southeast Arizona? In the half of the Sky Islands region that occurs in Mexico?
If the Sky Islands do indeed represent a conjunction of boreal and tropical forms, I ask, then how is that reflected in the moth fauna?
Noel’s ears perk up, I swear, almost like antennae. He guides my eyes to the noctuids again and begins to speak. The specimens before us are no longer static carcasses stuck on pins. Noel’s words effortlessly evoke the tropics, and within my mind I see these moths pushing north to accompany the rising heat and humidity of the summer monsoons. From July through September, sometimes October, these tropical beauties push into Arizona. Eggs are deposited on appropriate host plants. Some hatch into larvae that blend cryptically into lichens or flowers or leaves, while others display gaudy colors and ornamentation that cannot be ignored. If conditions permit, the newly hatched moths continue to push north, stopping to breed again if host plants and weather permit. It is as if there is a powerful drive pushing these pioneers.
The tropical pioneers have characteristics in common. They tend to be strong fliers, capable of feeding as they move. The sphinx moths, those hummingbird look-alikes, are fine examples, as are many of the noctuids. In contrast, the lasiocampids and saturnids have short-lived adults that lack functional mouthparts. Without mouths to feed, they lack the traits that make good pioneers. The geometrids tend to have good mouthparts but weak flight, so they rarely wander far from their larval latitudes.
I recall a fall day when I lived in Prescott Valley in central Arizona, well north of the Madrean Sky Islands. I noticed a dark creature with a five-inch wingspan pressed against the light-colored wall of the house. I approached, and it fluttered into the air, reminding me of some kind of bat. But when it landed, I saw that it was no mammal, even though it had two bold orange “irises” surrounding deep black “pupils”—false eyespots. This giant moth (a noctuid) had a velvety look, with rich purple tones overlying soft browns. It was one of the most beautiful and exotic creatures I had encountered. I delved into books and discovered I had been blessed by the visit of a Black Witch, Ascalapha odorata, normally a denizen of tropical and subtropical forests of Central and South America. Strong fliers, some of these moths wander north during our fall months, some even reaching Canada. The climate in the north, of course, is not presently suitable for them to persist and breed, but if global warming persists, then some day we may expect them to join the ranks of species breeding amidst the Sky Islands.
Since species diversity of so many types of organisms increases toward the tropics, then the influence of these tropical species can contribute much to local diversity. But Arizona is not the tropics, no matter how it feels along the lower San Pedro or the middle Gila in steamy August. Fall is followed by winter as inevitably as pupa follows larva. Cold snaps kill, and the range of each tropical species contracts, perhaps to the thornscrub along the lower Bavispe or the Río Sonora, only to expand again when warm monsoonal conditions return.
The dynamism of species’ ranges can best be appreciated through an exercise in creative seeing. Imagine that you could take elevate yourself well above the Sky Islands so you could see each of the several dozen ranges and their parallel valleys. Assume that each moth produces a pinpoint of light that you can distinguish. Erase all the lights belonging to resident species; their minor comings and goings may have ecological significance, but it’s the tropical species that interest us now.
Now speed up the action again. The photic tide surges north, then sags to the south. This goes on and on as annual cycles are repeated. But accelerate your temporal scanner again until what was an annual cycle is compressed into a decadal event, then a century event. At this scale, you can see more than mere repetition of pattern. You can see times in which the front curls around El Tigre in Sonora, right at the north end of the Sierra Madre, then retreats. For awhile, the pattern oscillates, sometimes more, sometimes less, but averaging right around the big bend of the Bavispe. After awhile, you see the average tide shift to the north. Before long, the peak surge is lapping at the bases of the Pajaritos, the Huachucas, the Chiricahuas. It may hold there for periods we could translate to decades or centuries, but it’s possible the surge could continue to push north, now lapping at the base of the Mogollon Rim. Then later the peak tides begin to slacken, the average northward push drops back to the south, perhaps leaving small populations of lights (moths) behind in refugia that continue to meet their needs.
Our exercise in informed imagination has just simulated the responses of tropical moths to climate change. Something like this must have occurred since the end of the Pleistocene: expansion of ranges to the north with warming, reaching a peak a few thousand years ago when warm moist conditions were at a maximum, then contracting as aridity and coldness pinched the moth pioneers back the way frost nips a bud.
The 1990’s were an exceptionally warm decade in North America, with particularly mild winters in southern Arizona; perhaps the tide of tropical moths that Noel has been witnessing shifted north accordingly. This is something we could document, if we were aware of the need to look! If competent naturalists recorded the comings and goings of the various forms of life, if we had data that we could put into a computer for visual analysis, then someone in the future could see on a screen just the type of patterns that I described. Our understanding of the factors that generate diversity in this region, or those that threaten that diversity, would allow us to manage our lands more wisely. It goes beyond moths, for patterns of distribution of birds, mammals, butterflies, and other taxa could be noted. If instead we collect no data, if we leave the computer screens to the world of virtual reality, then we could lose countless evolutionary lineages, not specimens that create pretty patterns in a collector’s box but complex forms of life and the stories each of them carries.
A day has now passed since my visit to see Noel McFarland. I am walking through a riparian area in pine-oak woodland in the Chiricahuas as steady rain falls. I duck beneath the boughs of small Chihuahua Pines, and bits of pale color flash erratically from the wet grasses in response to my passage. They are tiny moths, hundreds of them, disturbed by my feet, perhaps by the immensity of my size. This is their time, and for a moment I am in their world. It is a world of healthy grasses, regenerating trees, a world all too rare in this part of the continent. I think of the thousands of moth species on just five acres in Ash Canyon. I think of the subdivisions taking over land just like that, of other areas where cows have removed every blade of grass. I wonder how much diversity we have already lost, how many moths have disappeared, unknown and nameless, because there was no one like Noel McFarland there to bear witness.
Afterword: In June of 2011, a raging wildfire aided by absurdly low humidity and fierce, fickle winds roared up out of the south and engulfed Ash Canyon, destroying almost all of the homes, including that of moth expert McFarland. Buildings can be rebuilt and vegetation regrown (sooner or later depending on severity of soil sterilization), but three decades or more of insect collections and data—these are gone forever, a priceless loss of knowledge. Biotic information, ecological and genetic, is destroyed as surely as the neatly labeled boxes of moth specimens. It is obvious that the new Ash Canyon, rising from the ashes, will never be the same. There is a measure of resilience in nature, but in human lifespans, we will never see anything close to what existed there before. The loss to fire of one canyon, of course, is an event that has been repeated many times in the history of the Sky Islands, but the record fires in the Southwest in 2011 have multiplied the effects almost beyond our fears and imaginings. If we followed the metaphor of moth range expansion and contraction and applied it to many species across the vast landscape in these rapidly changing times, we would discover a new, dynamic pyrography of life. Yes, this requires us to bear witness.
This article appeared in 2011 in Restoring Connections 14(2):14-15. This is the fine publication of the Sky Island Alliance, which I encourage you to support.