Heelwalkers at home in South African biomes

Flyfeasting: A female Austrophasma gansbaaiensis gets to grips with dinner. Small they may be, but Heelwalkers are competent predators, stalking their prey from the base of plants (anything from a meaty fly to a succulent spider will do). But the insect is vulnerable to attack by birds, lizards and other insect carnivores, and are thus cryptic, remaining hidden at the base of grass tussocks.

A team of international scientists has found that South Africa is the centre of distribution for the newest insect order, Mantophasmatodea, a discovery announced to a captivated clique of zoologists and naturalists around the world, writes Helen Theron.

The last time a group of insects was described at this deep evolutionary level (ordinal level) was in 1914 when the Ice Crawlers (order Notoptera), a small group of insects restricted to ice caves in the northern hemisphere, were described. Studies are now underway to determine the closest relative of the Mantophasmatodea - and DNA evidence from an American research team suggests that their closest relative might in fact be the Ice Crawlers.

The number of documented "Heelwalkers", the common name derived from their habit of keeping the tarsal segments up in the air at all times, has also risen from four extant species (three Namibian and one Tanzanian species) to 13 species after the description of eight new species from South Africa, and one from Namibia.

The last time a group of insects was described at this deep evolutionary level (ordinal level) was in 1914 when the Ice Crawlers (order Notoptera), a small group of insects restricted to ice caves in the northern hemisphere, were described. Studies are now underway to determine the closest relative of the Mantophasmatodea - and DNA evidence from an American research team suggests that their closest relative might in fact be the Ice Crawlers.

The number of documented "Heelwalkers", the common name derived from their habit of keeping the tarsal segments up in the air at all times, has also risen from four extant species (three Namibian and one Tanzanian species) to 13 species after the description of eight new species from South Africa, and one from Namibia.

This was the result of extensive fieldtrips last year and during the spring of 2003 by zoology's Dr Mike Picker and a team of international colleagues, Klaus Klass (Dresden), Jakob Damgaard (Copenhagen), Rheinhard Predel and Steffen Roth (both from Jena), who form the South African Mantophasmatodea Project. Picker is responsible for the ecological and life history components of the study, and well as the systematics.

The group tramped a large arc of territory in search of the small creatures, a sweep that took in the Nama and Succulent Karoo, Beaufort West and Cape Infanta to the far south. Their findings confirmed that Heelwalkers occur in the fynbos, Succulent Karoo, Nama Karoo and thicket biomes of the Western Cape and Northern Cape.

To make life interesting, the Japanese Broadcasting Association (NHK) TV crew laboured in their footsteps. Their documentary will be released in January 2004. It focuses on the contribution of a Japanese colleague, Dr Koji Tojo, who is studying the embryology of Heelwalkers.

"NHK were not averse to recruiting helicopters for the odd aerial shot," Picker noted. "They obtained excellent footage, in spite of the unusually dry spring, which resulted in reduced insect numbers and flower displays."

To the untrained eye, the leggy Heelwalkers resemble juvenile praying mantids, so much so that entomologists in earlier years dismissed the few that they did collect as such. Two museum specimens, one in Tanzania and another in Namibia, were largely ignored before they were eventually rediscovered decades later. When Science magazine wrote about the insects in May last year, Picker realised he and his students had often encountered the small (body length 2-3 cm) creatures in South Africa. He recovered an additional 29 pinned specimens in dusty drawers in the South African Museum, gathered between 1890 and 1994.

Molecular studies by an American research team have shown that Mantophasmatodea are in a league (order) of their own. Based on the South African team's DNA analyses and studies of genitalic morphology, the higher classification within the Mantophasmatodea order was revised and two new families (Tanzaniophasmatidae and Austrophasmatidae) were created. The order now contains three families, 10 different genera, and 13 species. It is likely that this number will increase substantially after the specimens of the 2003 field season have been examined and sequenced, Picker says.

The insect's main characteristic, as borne out by its name, is that it walks on its heels. Other distinctive features include enlarged forelegs, armed with spikes, and very large eyes.

To attract a mate, Heelwalkers beat an amorous tapping call, which is probably perceived as a vibrational signal rather than as an airborne sound. Mating is a prolonged, complex process lasting one to three days. "In captivity, males are often eaten after mating, but this may be an artefact of the confinement of the pair in small mating chambers," Picker explained.

A number of species show colour polymorphism with specimens in the same population varying considerably in colour, depending on the natural habitat. The population of Austrophasma caledonensis near Caledon ranges from brown to green and white to green and cerise. The populations of Austrophasma gansbaaiensis and Lobophasma redelinghuysensis have both brown and green morphs, depending on whether they occur in sandveld or fynbos.

Females lay egg pods of 12 large eggs, held together by an amalgam of sand and hard "glue". Embryologist Toji Kojo has shown that the eggs have a unique water space that allows them to survive extensive summer drought. The first autumn rains trigger hatching.

The team will present their findings at the 22nd International Congress of Entomology in Brisbane, Australia, next year.

Exploring a new insect order is an experience few entomologists will enjoy in the 21st century. Such finds are very rare, although approximately only 50% or less of the world's insect fauna has been described.

"The discovery has unleashed huge popular interest," Picker confirmed. "But it's not just an important finding, it has opened up collaborative research opportunities with scientists from different countries having very different skills."

But with global warming threatening biomes such as the Succulent Karoo, home to many of these Heelwalkers, Picker is also looking ahead. "These insects represent a unique South African biological treasure, one that could be used as a flagship group for the conservation of the unique fauna and flora of the Succulent Karoo."

(The zoology department celebrates its centenary on November 20)