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African Tuesday: Heelwalkers

The first live heelwalker ever photographed – Gladiator (Tyrannophasma gladiator) from Brandberg, Namibia, which I photographed in March 2002 [Nikon D1x, Sigma 180mm]

The first live heelwalker ever photographed – The Gladiator (Tyrannophasma gladiator) from Brandberg, Namibia, which I photographed in March 2002 [Nikon D1x, Sigma 180mm]

After ice crawlers (featured in a recent post) were officially recognized as a new order of insect in 1915, entomologists pretty much assumed that this was it, and no more discoveries of such magnitude were expected. After all, an order is a major unit of classification – elephants, turtles, and flies are examples of orders – and so it was met with great skepticism when in 2002 another new order of insects was announced to the world by a team of German and Danish scientists. These strange new animals looked remarkably similar to ice crawlers, with their elongate, completely wingless bodies. But in their biology and behavior they could not be more different. The new insects, christened with the catchy moniker Mantophasmatodea, were found on the opposite side of the globe in the scorching deserts and shrubby vegetation of southern Africa. They were fast and agile and, unlike ice crawlers, predaceous and incredibly voracious.* They also walked funny, with the tips of their feet held up in the air, earning them the common name heelwalkers.

Habitat of the Gladiator on top of the Brandberg Massif in Namibia [Nikon D1x, Nikkor 17-35mm]

Habitat of the Gladiator on top of the Brandberg Massif in Namibia [Nikon D1x, Nikkor 17-35mm]

Through a mix of luck and pushiness I ended up on the first expedition to collect live heelwalkers in Namibia, and seeing them there, among hot rocks of the Brandberg Massif was definitely one of the highlights of my life. (I also learned something valuable that time: if you stand in the middle of a dry riverbed and hear some strange noise getting louder, run like hell, it is a flash flood coming.) In the years that followed many scientists carefully looked at the minutiae of the bodies and genes of the Mantophasmatodea, and both molecular and morphological analyses confirmed their close relatedness to ice crawlers. So close is this relationship that these two orders of insects are considered “sister groups”—two distinct lineages of organisms that diverged from a single common ancestor. As such, and considering how few species each of these orders contains, some entomologists now prefer to combine Grylloblattodea (ice crawlers) and Mantophasmatodea (heelwalkers) into a single order. When such an option was first discussed, I heard at one scientific meeting the name Gryloblattomantophasmatodea being briefly considered for the combined order. I almost wish it had been chosen, so outrageously long and yet entirely inaccurate it would have been; translated from Latin, the name means “cricket-cockroach-preying mantis-walking stick-like insect,” four groups to which neither ice crawlers nor heelwalkers are closely related!

Kuduberg heelwalker (Mantophasma kudubergense) from Namibia [Nikon D1x, Sigma 180mm]

Kuduberg heelwalker (Mantophasma kudubergense) from Namibia [Nikon D1x, Sigma 180mm]

Since the initial discovery of heelwalkers in 2002, about 20 additional species have been found, mostly in South Africa where, as it turned out, in some places they were as common as dirt. How and why entomologists overlooked them for so long is a perplexing question, the answer to which appears to be surprisingly mundane. Not long ago I was in South Africa conducting a survey of katydids in the fynbos. My friend Corey and I drove along the coast, stopping every now and then to look for katydids and grasshoppers on the side of the highway. It was the end of southern winter, dry and often cold at night. Few insects are active in this season, and those that you find are often juveniles. But soon we struck gold—first one, then another, and eventually six new-to-science species of small, flightless katydids (Brinckiella) turned up in the bushes—an entire unexpected radiation of these insects. Entomologists have collected katydids in South Africa for ages; how could have they missed these? I pondered this question as I slowly scanned the vegetation looking for more insects. Suddenly, I found myself eye to eye with a chubby, green female heelwalker. She sat on a branch at eye height, motionlessly trying to blend into her surroundings. Although I knew she was a fully grown adult, she somehow looked larval. The combination of the lack of wings, stubby appearance, and the fact that she was out and about in the middle of winter, all this seemed to suggest that this insect was immature. And that was it. That was the reason these insects had escaped notice for so many years. Like our flightless katydids, similar to juveniles of species active in the spring and summer months, heelwalkers had been occasionally collected by entomologists but quickly discounted as immature forms of something else and stuffed into the darkest corners of entomological collections. Sure enough, after the publication of the official description of the first heelwalkers, many specimens were discovered in South African museums, some collected more than a century earlier. After Corey and I returned from our field trip, I paid a visit to the Iziko South African Museum in Cape Town, and there, among unidentified immature insects were dozens of the new katydids, some having sat there, unrecognized, for more than seventy years.

Kuduberg heelwalker (Mantophasma kudubergense) from Namibia [Nikon D1x, Sigma 180mm]

Kuduberg heelwalker (Mantophasma kudubergense) from Namibia [Nikon D1x, Sigma 180mm]

Undoubtedly, the coming years will see new species of heelwalkers discovered and volumes of new data on their ecology and behavior published. But we may need to hurry. Like the melting and disappearing environment of ice crawlers, there are signs that heelwalkers’ habitats are threatened as well. The ancient, unique, and unbelievably rich South African plant communities of karoo and fynbos, homes of so many plant species that they earned the entire region the designation Cape Floral Kingdom, are shrinking. Development, desertification, and mining steadily strip the precious ecosystem bit by bit, literally pushing it into the ocean. Heelwalkers, with their fifteen or so known species, each restricted to a tiny patch of unique Cape vegetation, may soon be in a serious quagmire. The same Mesozoic forbearer that gave rise to ice crawlers—and their narrow ecological specialization—produced another organism that, although it occupies an entirely different niche, is also dangerously specialized. And this, as the rich fossil record of specialized lineages clearly shows us, is a recipe for extinction.

A yet undescribed species of heelwalker (Sclerophasma sp.) from South Africa [Canon 1D MkII, Canon 100mm macro, 2 speedlights Canon 580EX]

A yet undescribed species of heelwalker (Sclerophasma sp.) from South Africa [Canon 1D MkII, Canon 100mm macro, 2 speedlights Canon 580EX]

[An excerpt from my book “Relics: Travels in Nature’s Time Machine“]

*) Entomologist Mike Ivie pointed out that ice crawlers can be equally fast and voracious, recalling his experience with these insects: “…we fed them live flies and they got them every time, and eat until they practically burst.”

Ice-crawlers

Ice crawler Grylloblatta campodeiformis from Alberta, Canada. [Canon 10D. Canon 100mm, ambient light]

Ice crawler Grylloblatta campodeiformis from Alberta, Canada. [Canon 10D. Canon 100mm, ambient light]

Entomologists, unlike birders, usually do not keep life lists of insects, but seeing my first ice crawler (Grylloblattodea) was akin to checking off the first kiwi on a twitcher’s life list. These insects are a strange breed. Only twenty-eight species are known, and they are found only in colder regions of North America and the Far East of Asia. The American species live mostly along the northern coast of the United States and Canada, in the Cascade and Sierra Nevada ranges. There you can find them on northern talus slopes of mountains, as high as three thousand meters or in ice caves.

Grylloblatta

The North American snow-associated species of ice crawlers have very well-developed eyes. These insects are active both during the day and at night and use visual and olfactory cues to find food as they walk on the snow’s surface. [Canon 10D. Canon 100mm, ambient light]

These insects clearly love cold weather. Their optimal temperature of activity hovers around the freezing point, and you can easily kill one by touching it due to the warmth of your hand. And yet they are also not really good at surviving in the extreme cold — a drop in the temperature to below -9°C will also cause them to die. Unlike other cold-loving insects they have never evolved the appropriate levels of glycerol and other antifreezing compounds in their blood. And so, like tiny, six-legged Goldilocks, they seem relegated to a life in narrow, fleeting ranges of environmental variables, constantly searching for just the right temperature and humidity.

But a life like this has its advantages: because of their slow, temperature-dependent metabolism, ice crawlers are surprisingly long-lived (for insects) and may reach the ripe age of ten years. Food is usually not a problem as ice crawlers will eat almost anything, ranging from dead insects blown onto the surface of the ice to vegetal matter found under snow. There is not much competition in the subfreezing layers of the soil, especially if you are the largest insect active in this environment, and most predators, such as shrews or toads, tend to stay away from really cold places. Asian species of ice crawlers have slightly higher temperature tolerance and can safely live in the span of 9–15°C. Because many other animals are also active within this range, Asian ice crawlers escape competitors and predators by hiding very deep in the soil or at the bottom of caves.

In contrast to North American species, the fossorial Asian species, like this Japanese Galloisiana nipponensis, which spend their entire life deep underground, are blind and never forage on the surface. [Canon 1Ds MkII, Canon MP-E 65mm, 2 speedlights Canon 580EX]

In contrast to North American species, the fossorial Asian species, like this Japanese Galloisiana nipponensis, which spend their entire life deep underground, are blind and never forage on the surface. [Canon 1Ds MkII, Canon MP-E 65mm, 2 speedlights Canon 580EX]

But in the beginning, the life of these insects used to be very different. Over 250 million years ago, in the Permian, the ancestors of modern ice crawlers were anything but crawlers on ice. For one, all ancient species were equipped with two pairs of large wings. Based on the analysis of the gut content of some remarkably well preserved fossils we know that they fed primarily on pollen of ancient conifers and some of their now-extinct relatives. For millions of years they flourished in hot, tropical parts of the globe, leading a plant-hopping life, quite likely similar to that of many of today’s pollinators. According to some entomologists there used to be as many as 44 families of “ice crawler”–like insects, compared to a single family known today. They are frequently found in rock deposits dating back from the Permian to the Cretaceous.

Cool, shady, and humid subalpine and alpine valleys in the beautiful Chichibu-Tama-Kai National Park not far from Tokyo are an example of the typical habitats of Japanese ice crawlers. [Canon 1Ds MkII, Canon 16-35mm]

Cool, shady, and humid subalpine and alpine valleys in the beautiful Chichibu-Tama-Kai National Park not far from Tokyo are an example of the typical habitats of Japanese ice crawlers. [Canon 1Ds MkII, Canon 16-35mm]

But then, gradually, they disappeared from the fossil record. Strangely, there is not a single ice crawler known from the period after mid-Cretaceous. Their disappearance coincides roughly with the appearance of flowering plants, or angiosperms, and the nearly concurrent diversification of beetles and other plant pollinators. It seems that rather than allowing themselves to be outcompeted by this new army of more advanced plant-associated insects, the ancestors of ice crawlers found survival in a completely new lifestyle.

Japanese species of ice crawlers, or garoamushi, are distinctly larger than their American counterparts and, because of their higher metabolic rates, faster and more difficult to catch. The species most common in Japan is Galloisiana nipponensis. Garoamushi are found primarily in areas that have a mean annual temperature of 12°C, but even in these cool areas they hide deep in the soil throughout most of the year. [Canon 1Ds MkII, Canon MP-E 65mm, 2 speedlights Canon 580EX]

Japanese species of ice crawlers, or garoamushi, are distinctly larger than their American counterparts and, because of their higher metabolic rates, faster and more difficult to catch. The species most common in Japan is Galloisiana nipponensis. Garoamushi are found primarily in areas that have a mean annual temperature of 12°C, but even in these cool areas they hide deep in the soil throughout most of the year. [Canon 1Ds MkII, Canon MP-E 65mm, 2 speedlights Canon 580EX]

They shed their wings and entered a chilly, inhospitable niche along the edges of glaciers, in caves, or deep in the soil. This explains the lack of a fossil record; fossilization usually requires the sinking of a dead organism into fine silt at the bottom of a lake or an ocean, and so the environments favored by ice crawler ancestors made fossil formation difficult.
Although they have been luckier than all their winged, plant-hopping ancestors, the luck of modern ice crawlers may soon run out. Their dependence on a very narrow spectrum of low temperatures, combined with their inability to fly and thus quickly colonize new habitats, may soon spell the end of this ancient lineage in our rapidly warming world. As sometimes happens in evolution, ice crawlers have painted themselves into a corner. During the Pleistocene, when most of the North American continent was covered with a thick ice cap, these insects probably survived only on the edges of the glacier or in underground networks of caves. As the ice receded they followed it and colonized suitably cold (but not too cold) places high on mountain slopes or in icy caves. As a result, populations of these insects tend to be small and genetically isolated from each other due to the island-like nature of cold, alpine habitats. This means that when their environment suddenly becomes uncomfortably warm—and there is already ample evidence of the shrinking of North American glaciers—they have nowhere to go. And even if there still existed available habitats, ice crawlers have no way of getting there because of their inability to fly. Some populations in the Sierra Nevada of California, perhaps entire species of ice crawlers, may already be extinct, as repeated attempts to find them during the last forty years have failed. And when the entire genetic makeup of a lineage consists of only twenty-eight species, every one of them is priceless.

[An excerpt from my book “Relics: Travels in Nature’s Time Machine“]