Vermileonidae
Encyclopedia
The Brachycera
n family Vermileonidae (the sole member of the infraorder Vermileonomorpha) is a small family of uncertain affinities and unusual biology, containing fewer than 80 rare species in 10 genera. Historically the Vermileonids had been regarded as belonging to the family Rhagionidae, possibly in a subfamily Vermileoninae. Their biology and morphology is so markedly distinct from the main Rhagionidae sensu stricto, that the placement as a separate family has been widely accepted.
The larva
e of Vermileonids are called wormlions which amounts to a direct translation of "Vermileo". They have evolved the same elaborate mechanism for trapping prey, as one sees in many species of the Neuroptera
n family Myrmeleontidae, the so-called "ant-lions"; that is, they make cone-shaped "pits" in sandy areas and feed on insects that fall into the pits. The mechanism is elegant in that in both groups of insects the larva creates the pit by flinging particles out. Much of the material falls back, coming to rest at effectively the critical Angle of repose
.
Thus, when a small insect, commonly an ant, blunders into the pit, its weight causes the sand to collapse below it, drawing the victim toward the center where the larva lies in wait under a thin layer of loose sand. As soon as it is alerted by falling sand grains, the larva assists this process by vigorously flicking more sand out from the center of the pit. This undermines the pit walls and causes them to collapse toward the center. The sand that the larva now is flinging also pelts the prey with so much loose, rolling material as to prevent it from getting any foothold on the easier slopes that the initial collapse of the slope has presented. The combined effect is to bring the prey down to within grasp of the larva, which then can inject venom and digestive fluids.
Unlike the pit-digging Myrmeleontidae, Vermileonid larvae do not travel round and round while digging the pit trap. Instead they simply lie at the centre with the rear end buried, and dig their heads repeatedly into the sand, flinging it out by vigorously straightening their fore-ends. Finally they cover themselves with a thin layer of sand while lying across the bottom of the cone.
The main enemies of the larvae of either ant lions or worm lions are ground-hunting birds such as hoopoe
s and gallinaceous birds
that learn to recognise their pits and probe or scratch them from the sand. If alarmed by such activity, the worm lion larva retracts abruptly into an S-shape under the sand, and if dug out it retains that shape, not having much option for an alternative strategy at its disposal. Actually, because its skin is coated with sand, and it is very small, it is very easy to overlook while it lies still. However, if it is sufficiently teased after being dug out, it may begin to lash about powerfully, flinging itself away with enough force to escape its tormentor. It does not however hook its mouthparts into its hinder end to achieve an efficient leap such as some fruit fly and carrion-fly larvae do.
The tenth and eleventh segments of the larva each carries a transverse row of long hooklets that it uses in anchoring itself and in shifting sand. The fifth segment has a ventral pseudopod that helps to hold prey. Not having sickle jaws like an ant lion, the larva grasps prey by lashing forward and catching the victim by bending the head down to catch it between its two fang-like jaws and its pseudopod.
Like ant lion larvae, Vermileonid larvae are primarily found in sandy habitats, often semi-deserts, usually in the shelter of rocks or bushes, and they are voracious predators. The adults are slender, fragile flies, vaguely reminiscent of small crane flies
. The adults generally visit flowers for nectar, but adults of some species may not feed at all.
Most Vermileonid species are found in the drier regions of the Western parts of Africa, from the Cape to Morocco, and also in the Western parts of the Iberian Peninsula, mainly in Portugal.
, though the most recent classifications place them as its sister taxon.
Brachycera
Brachycera is a suborder of Diptera. It is a major suborder consisting of around 120 families. The most distinguishing characteristic of the suborder is reduced antenna segmentation...
n family Vermileonidae (the sole member of the infraorder Vermileonomorpha) is a small family of uncertain affinities and unusual biology, containing fewer than 80 rare species in 10 genera. Historically the Vermileonids had been regarded as belonging to the family Rhagionidae, possibly in a subfamily Vermileoninae. Their biology and morphology is so markedly distinct from the main Rhagionidae sensu stricto, that the placement as a separate family has been widely accepted.
The larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e of Vermileonids are called wormlions which amounts to a direct translation of "Vermileo". They have evolved the same elaborate mechanism for trapping prey, as one sees in many species of the Neuroptera
Neuroptera
The insect order Neuroptera, or net-winged insects, includes the lacewings, mantidflies, antlions, and their relatives. The order contains some 6,010 species...
n family Myrmeleontidae, the so-called "ant-lions"; that is, they make cone-shaped "pits" in sandy areas and feed on insects that fall into the pits. The mechanism is elegant in that in both groups of insects the larva creates the pit by flinging particles out. Much of the material falls back, coming to rest at effectively the critical Angle of repose
Angle of repose
The angle of repose or, more precisely, the critical angle of repose, of a granular material is the steepest angle of descent or dip of the slope relative to the horizontal plane when material on the slope face is on the verge of sliding. This angle is in the range 0°–90°.When bulk granular...
.
Thus, when a small insect, commonly an ant, blunders into the pit, its weight causes the sand to collapse below it, drawing the victim toward the center where the larva lies in wait under a thin layer of loose sand. As soon as it is alerted by falling sand grains, the larva assists this process by vigorously flicking more sand out from the center of the pit. This undermines the pit walls and causes them to collapse toward the center. The sand that the larva now is flinging also pelts the prey with so much loose, rolling material as to prevent it from getting any foothold on the easier slopes that the initial collapse of the slope has presented. The combined effect is to bring the prey down to within grasp of the larva, which then can inject venom and digestive fluids.
Unlike the pit-digging Myrmeleontidae, Vermileonid larvae do not travel round and round while digging the pit trap. Instead they simply lie at the centre with the rear end buried, and dig their heads repeatedly into the sand, flinging it out by vigorously straightening their fore-ends. Finally they cover themselves with a thin layer of sand while lying across the bottom of the cone.
The main enemies of the larvae of either ant lions or worm lions are ground-hunting birds such as hoopoe
Hoopoe
The Hoopoe is a colourful bird that is found across Afro-Eurasia, notable for its distinctive 'crown' of feathers. It is the only extant species in the family Upupidae. One insular species, the Giant Hoopoe of Saint Helena, is extinct, and the Madagascar subspecies of the Hoopoe is sometimes...
s and gallinaceous birds
Galliformes
Galliformes are an order of heavy-bodied ground-feeding domestic or game bird, containing turkey, grouse, chicken, New and Old World Quail, ptarmigan, partridge, pheasant, and the Cracidae. Common names are gamefowl or gamebirds, landfowl, gallinaceous birds or galliforms...
that learn to recognise their pits and probe or scratch them from the sand. If alarmed by such activity, the worm lion larva retracts abruptly into an S-shape under the sand, and if dug out it retains that shape, not having much option for an alternative strategy at its disposal. Actually, because its skin is coated with sand, and it is very small, it is very easy to overlook while it lies still. However, if it is sufficiently teased after being dug out, it may begin to lash about powerfully, flinging itself away with enough force to escape its tormentor. It does not however hook its mouthparts into its hinder end to achieve an efficient leap such as some fruit fly and carrion-fly larvae do.
The tenth and eleventh segments of the larva each carries a transverse row of long hooklets that it uses in anchoring itself and in shifting sand. The fifth segment has a ventral pseudopod that helps to hold prey. Not having sickle jaws like an ant lion, the larva grasps prey by lashing forward and catching the victim by bending the head down to catch it between its two fang-like jaws and its pseudopod.
Like ant lion larvae, Vermileonid larvae are primarily found in sandy habitats, often semi-deserts, usually in the shelter of rocks or bushes, and they are voracious predators. The adults are slender, fragile flies, vaguely reminiscent of small crane flies
Crane fly
A crane fly is an insect in the family Tipulidae. Adults are very slender, long-legged flies that may vary in length from though tropical species may exceed to ....
. The adults generally visit flowers for nectar, but adults of some species may not feed at all.
Most Vermileonid species are found in the drier regions of the Western parts of Africa, from the Cape to Morocco, and also in the Western parts of the Iberian Peninsula, mainly in Portugal.
Classification
The infraorder Vermileonomorpha is often included within the TabanomorphaTabanomorpha
The Brachyceran infraorder Tabanomorpha is a small group that consists primarily of two large families, the Tabanidae and Rhagionidae , and an assortment of very small affiliated families, most of which have been included within the Rhagionidae...
, though the most recent classifications place them as its sister taxon.