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.
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!
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.
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.
[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.”