Mantophasmatodea (Heel-Walkers or Gladiators)
Mantophasmatodea (Heel-Walkers or Gladiators)
(Heel-walkers or gladiators)
Number of families 3
Evolution and systematics
The order Mantophasmatodea (heel-walkers, gladiators) was discovered in 2001 and formally described in 2002 based on two specimens that had been stored for decades in the natural history museums of Berlin and Lund (Sweden). With its 12 extant species, assigned to nine genera and three families, the Mantophasmatodea is the smallest insect order. The closely related genera Namaquaphasma (one species), Karoophasma (two species), Lobophasma (one species), Hemilobophasma (one species), and Austrophasma (three species) comprised in the family Austrophasmatidae, differ in details of the male and female genitalia. The genera Mantophasma (one species) and Sclerophasma (one species), which together constitute the family Mantophasmatidae, as well as Tanzaniophasma (one species) all display striking percularities in the copulatory organs. Praedatophasma (one species), whose systematic placement is unresolved, is unique in its spiny thorax ("gladiator").
The only known fossil genus is Raptophasma (two species) from Baltic amber, which is about 45 million years old. These creatures resemble extant Mantophasmatodea, but the thornless legs constitute a conspicuous difference. Using other insect orders as a measure, the origins of Mantophasmatodea probably go back to much earlier times.
Anatomical details of the abdominal spiracles and the ovipositor of the female, for example, show that despite lacking wings, the Mantophasmatodea belong to the Pterygota, the group comprising all winged insects as well as many that have lost their wings secondarily (such as Mantophasmatodea). It is unclear which other insect order is the closest relative of the Mantophasmatodea; the ice-crawlers (Grylloblattodea) and the stick insects (Phasmida) are the most likely candidates.
The consistently wingless Mantophasmatodea have a very uniform body shape, which superficially resembles that of certain grasshoppers or stick insects. The body length (without the antennae) ranges from 0.35 to 0.94 in (9–24 mm), males usually being somewhat smaller than females. The basic color of the body is brown, gray, green, or yellow; different tints of these colors, a whitish component of varied extent, and— in some species—black dots form a pattern of mottles and/or longitudinal stripes. Coloration varies between and also within species. Nymphs resemble the adults in appearance.
The antennae are long and have many segments. The compound eyes are well developed, albeit of varied size, but ocelli are lacking. The chewing mouthparts are generalized and directed downward. The femora are distinctly thickened in the forelegs and somewhat thickened in the midlegs, but they are very slender in the hind legs. The tibiae of the forelegs and midlegs bear on their inner surfaces (opposing the femora) two rows of short thorns, which render the legs suitable for grasping other insects. The tarsi comprise five tarsomeres, but the three basal ones are fused (with grooves indicating the borders). A large adhesive lobe (arolium) originates from between the claws.
The abdomen consists of 10 well-developed segments and a reduced eleventh segment. In the females, segments eight and nine bear three pairs of processes (valves) that together
form a short ovipositor. The second and third valves are largely fused, and the latter are very hard and conspicuously claw-shaped. The genital opening lies behind the eighth sternite, which forms a subgenital plate. In the male, the ninth sternite is elongated to form a subgenital plate, which covers the retracted, largely membranous male genitalia ventrally. For copulation the genitalia become everted, thus displaying two or three small sclerites and two small sclerotized hooks. The one-segmented cerci are short in the female but fairly long and curved in the male, which uses them as accessory copulatory structures. The tenth abdominal tergum, which bears the muscles moving the cerci, is much wider in the male than in the female. While the middle part of the abdomen is widest in females (because it harbors the ovaries), in males the hindmost part usually is widest due to the expanded tenth tergum.
Derived features distinguishing Mantophasmatodea from other insects are the location of the anterior tentorial pits (anterior invagination points of the endoskeleton of the head) far above the mandibular articulation, a peculiarly shaped differentiation of the antennae (e.g., with differently shaped basal and distal segements) and a rounded projection on the middle of the male's subgenital plate.
Extant Mantophasmatodea are known only from Africa: Namibia (two species), westernmost South Africa (eight species), and Tanzania (one species). Raptophasma from Baltic amber shows, however, that in the early Tertiary the group also occurred in Europe. The species recorded from South Africa seem to occupy fairly restricted, mutually largely exclusive geographic areas. This high degree of endemism renders the Mantophasmatodea a very interesting group for studies of the biogeographical history of southern Africa.
Mantophasmatodea inhabit three of the major biomes found in western South Africa and Namibia: nama karoo, succulent karoo, and fynbos. The former location is characterized by (poor) summer rainfall and the two latter by winter rainfall (poor in succulent karoo), but all are moderately or extremely dry throughout the rest of the year and almost bare of trees. Broad differences between temperatures during the day and at night (with frost in winter) are normal. During and shortly after the humid season, the species-rich
flora and fauna bloom. Localities harboring Mantophasma-todea show a wide range of vegetation density. Some species frequently are found in tufts of grass (Poaceae) or Cape reed (Restionaceae, which superficially resemble grasses); they occur either at the bottom between the culms or on top of the culms, where they are well camouflaged by their mottled and striped coloration. The habitat of the Tanzanian Tanzanio-phasma subsolana is unknown.
Mantophasmatodea essentially live singly, but a male and a female often can be found together in the same tuft of grass, and within suitable habitats an area of several hundred square yards (meters) may harbor a sound population while no heel-walkers are found in the surrounding areas. There appears to be both nocturnal and diurnal activity. Movements typically are quite slow, but they can be rapid when prey is caught or a male mounts a female for copulation. When walking, Mantophasmatodea generally have their basal tarsomeres on the ground, while the fifth tarsomeres and the terminal claws and arolia are held in an elevated position (hence the name heel-walkers). The males use the projection of their subgenital plates to knock on the ground, which may serve for communication.
Feeding ecology and diet
Mantophasmatodea eat other insects of various kinds, up to their own size. They grasp and hold them by means of their powerful, spiny forelegs, additionally using the midlegs for large prey. Each mandible has a sharp edge for cutting the victim to pieces; all parts, except the legs and wings are devoured. Cannibalism also occurs.
Courtship is unknown. For copulation the male jumps onto the female and bends his abdomen aside and downward to bring his copulatory organs into contact with the hind part of the female's abdomen. The act of copulation, with the male sitting on the female's back, can last up to three days. The female then produces several sausage-shaped egg pods, which contain about 10–20 long, oval eggs covered by a hard envelope made from sand and gland secretions. The ovipositor serves for shaping the egg pod and for proper placement of the eggs into it. The nymphs hatch at the beginning of the rainfall period, molt several times, reach maturity near the end of the humid season, and die during the early dry period. Consequently, life cycles are diametrically different depending on whether precipitation falls predominantly in summer or in winter.
As of 2002, no species of Mantophasmatodea were listed on the IUCN Red List. Mantophasmatodea are not uncommon in Namibia and western South Africa. Nothing is known, however, about how common the various species are. The apparently small distribution areas of some species might make them sensitive to extinction. Nonetheless, the finding of a rich population immediately alongside a road indicates that not all species suffer from this aspect of human civilization. Only a single specimen has been recorded from Tanzania, and it is unknown how common Mantophasmatodea are in this part of Africa.
Significance to humans
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Klaus-Dieter Klass, PhD