The Asilidae are the robber fly family, also called assassin flies. They are powerfully built, bristly flies with a short, stout proboscis enclosing the sharp, sucking hypopharynx.[1][2] The name "robber flies" reflects their expert predatory habits; they feed mainly or exclusively on other insects and, as a rule, they wait in ambush and catch their prey in flight.
Overview
Zosteria sp.A member of the Asilidae feeding on a grasshopper. This asilid shows the mystax and ocular fringe typical of the Asilidae, with short, stout proboscis and spiny, powerful legs, adapted to the capture of prey in flight.
The Asilidae are a family in the orderDiptera, the true flies. The common name for members of the family is the robber flies. The Asilidae are cosmopolitan, with over 7000 described species. Latreille was the authority for establishing the family in 1802.[3] The Asilidae, together with Bombyliidae and Therevidae, are the most representative families of the superfamily of Asiloidea and they form one of the most characteristic groups of the lower Brachycera.
Robber flies have stout, spiny legs and three simple eyes (ocelli) in a characteristic depression on the tops of their head between their two large compound eyes.[4] They also have a usually dense moustache of stiff bristles on the face; this is called the mystax, a term derived from the Greek mystakos meaning "moustache" or "upper lip". The mystax has been suggested to afford some protection for the head and face when the flies deal with struggling prey; various Asilidae prey on formidable species including stinging Hymenoptera, powerful grasshoppers, dragonflies and even other Asilidae, in fact practically anything of a suitable size. Some Asilidae do, however, specialize in smaller prey, and this is reflected in their more gracile build.
In general, the family attacks a very wide range of prey, including other flies, beetles, butterflies and moths, various bees, ants, dragonflies and damselflies, ichneumon wasps, grasshoppers, and some spiders. They do so apparently irrespective of any repugnatorial chemicals the prey may have at their disposal.[5] Many Asilidae when attacked in turn do not hesitate to defend themselves with their probosces and may deliver intensely painful bites to humans if handled incautiously.
The antennae are short, have three segments, and sometimes bear a bristle-like structure called an arista.
Though they are a very characteristic group for such a large family, the Asilidae may easily be confused with the related and less widely known family Therevidae. Some points of contrast between the families include that the labium in the Therevidae is not a piercing, predatory organ, but ends in two fleshy labella adapted to the sucking of liquid foods. Again, the Therevidae commonly have fluffy setae above the mouthparts, unlike the stiff chaetae comprising the mystax of the Asilidae. Furthermore, in the Asilidae the depression on the vertex between the eyes tends to be more obvious than in the Therevidae.
A male Laphria flava feeding on a Rhynocoris annulatus
The fly attacks its prey by stabbing it with its short, strong proboscis, injecting the victim with saliva containing neurotoxic and proteolytic enzymes which very rapidly paralyze the victim and soon digest the insides; the fly then sucks the liquefied material through the proboscis.
Many Asilidae have long, tapering abdomens, sometimes with a sword-like ovipositor. Others, for instance Laphria, are fat-bodied bumblebee mimics.
Female robber flies deposit whitish-colored eggs on low-lying plants and grasses, or in crevices within soil, bark, or wood. Egg-laying habits depend on the species and their specific habitat; most species lay their eggs in masses, which are then covered with a chalky protective coating.
After hatching, robber fly larvae generally seem to live in soil, rotting wood, leaf mold, and similar materials, some being predatory and others detrivorous.[5] Larvae are also predacious, feeding on eggs, larvae, or other soft-bodied insects. Robber flies overwinter as larvae and pupate in the soil. Pupae migrate to the soil surface and emerge as adults, often leaving behind their pupal casing. Complete development ranges from one to three years, depending on species and environmental conditions.[6]
Morphology
Adult
Adults are generally medium to large in size, with an average body width of 1 to 1.5cm (0.39 to 0.59in), but with a range of 3mm (0.12in) to more than 5cm (2.0in) in length. The shape is generally elongated, due to the conformation of the long tapering abdomen, however there are also compact species with broad abdomens. The integument is covered with thick hair, especially on the head and thorax and liveries are often showy, with colors ranging from brown to black to grey, sometimes in contrast with other colors such as red and yellow. Frequently they are aposematic, imitating the livery of Hymenoptera.
Choerades fimbriata: a powerful predator with body adapted to fast flight. Note the mystax, the proboscis and the depression between the eyes.Head-on view showing the characteristic depression formed by the elevation of the compound eyes
The head is free and mobile and dichoptic in both sexes and has three ocelli arranged in a characteristic depression formed by the elevation of the compound eyes. This feature is clearly visible in the front view and is a morphological peculiarity of Asilidae. The occipital region has one or more rows of bristles aligned behind the posterior margin of the eye. The facial region has a convex profile with a characteristic dense bundle of bristles, called a "mystax". The mystax helps protect the head and face when the fly encounters prey bent on defense. Other bristles are arranged on the ocellar tubercle.
The antennae are of the aristate type, composed typically of five segments but sometimes from three to four, depending on the structure of the stylus. The scape and pedicel are generally relatively short and hairy; the third segment (or first flagellomere) has an oval or oblong shape, is generally longer than the two basal segments, and bears a stylus generally composed of two segments, of which the basal is very short. In some asilids, the stylus can be monoarticolate or absent.
The mouthparts are short and modified for piercing-sucking. They consist of a strongly sclerotized proboscis which includes the labium and maxillae which form a food canal, the labrum and a piercing organ, the hypopharynx. The proboscis is rounded in cross section or laterally or dorsoventrally compressed and is usually stout, and straight and sometimes able to penetrate through the hard integument of Coleoptera. The maxillary palpi are at the base beside the labium, two-segmented in all Dasypogoninae or single segmented in Asilinae and Leptogastrinae.
The thorax is robust and compact. Unlike in other lower Brachycera, it bears long bristles (macrochaeta) useful as taxonomic characters. Bristles of this type are always present on the notopleuron (notopleural bristles) and, in two series, on mesonotum (dorsocentral, supralar and postalar). Other bristles are present on the metanotum (dorsocentral bristles on the ventral episternum and at the apex of the mesoscutellum.
The legs are relatively long and strong, with many macrochaetes performing a raptorial function. The wings are well developed, often relatively narrow for speedy flight; the alula is generally well developed, with the exception of the Leptogastrinae and part of Dasypogoninae. The venation is much as in the Rhagionidae, Tabanidae, and Therevidae; the radial R is always four-branched, with R2+3 unbranched. Details of wing venation determine subfamilies and lower taxa. The wings are most often hyaline, but sometimes smoky or dark colored, or partly infuscated in many genera or completely darkened. The abdomen consists of six to eight visible segments preceding the genitalia in males, but the eighth segment is sometimes entirely or partially concealed, and terminal forming the ovipositor. It is long and narrow conical in most species, but wide, dorsoventrally flattened and short in bee mimics. In the Leptogastrinae, the abdomen is extremely long and slender. In some tribes, the male undergoes axial torsion of 180°.
Egglaying
Egg
The egg is hyaline or pigmented and of variable shape from spherical to oval and up to 2mm in length. The surface is smooth or bears microsculptures, which are generally polygonal and visible only in the electron microscope.
Larva
The larva is apodous, cylindrical, and elongated, more or less flattened dorsoventrally and tapered at the cephalic and caudal ends. The colour is white or yellowish. The head is small, rugged, dark-pigmented and hypognathous, the abdomen is composed of eight apparent urites, with the last two often fused and more or less reduced. The respiratory system is amphineustic, with two pairs of spiracles, one thoracic and one abdominal. Also, rudimentary and nonfunctional stigmata occur in other abdominal segments.
Pupa
The pupa is naked, as in the majority of the Orthorrhapha, exarate and therefore able to move.
Biology
The Asilidae are predators, in both the juvenile and the adult stages, and feed on small arthropods, mainly insects. Although predatory forms in the adult stage are present in other taxonomic groups of Diptera, the Asilidae are the most representative for the number of species and for uniformity of feeding behavior (>7000 species, all of which are predatory). The combination of high biodiversity and high predatory activity leads to this family playing an important role in the ecological stability of entomofauna.
Blepharepium sonorensis, a robber fly that closely resembles Polistes paper wasp species such as P. apachus
The life cycle takes place in 1–3 years. The postembryonic development consists of four larval stages (instars) and one pupa. The larvae of the first instar differ from other stages in both ethology and trophic regime. The larvae of most known asilids live in the soil or in the case of some taxonomic groups, in rotting organic material, usually wood and the bark of dead trees.
With regards to feeding behavior, most of the literature describes Asilidae larvae as entomophagous, but doubts remain about the real nature of the trophic regime and its mechanisms. The entomophagy of some species had indeed been already hypothesized by some authors of the 19th century, based on the findings of larvae of asilids associated with larvae of other insects, but Melin (1923) asserted that, in reality, predation was occasional and secondary to the plant-based diet. More recent studies have confirmed the entomophagy of some asilids without extending this species' feeding behavior for the whole family. Less certain, however, is the mechanism of entomophagy: in general, the behavior is cited as predation, but for some species may be ectoparasitoids. Musso (1983)[7] described the feeding behavior of the larvae of Machimus rusticus: the larvae of the first instar does not feed on insects, those of the second instar feed on secretions by larvae of beetles (and may cause death), while the larvae of the third and fourth instars actually behave like predators. In short, the feeding behavior of larval asilids can be intermediate between predation and ectoparasitism.
Much better known and described in detail is the behavior of adults. In general, predation in adults is concentrated in the hottest hours in open, sunny spaces, while at night, they take refuge in dense vegetation. The Asilidae are excellent flyers, and in most of the family, capture prey in flight. They are often seen stationed to ambush prey at strategic points. This behavior signifies that sight plays an essential role in the detection of prey and their capture.
A robber fly with a honey bee. Includes slow motion.
The prey is caught with the tarsi and injected with a paralyzing saliva. The asilid pierces the integument of the prey with the prepharyx (hyopharynx) in preferential points of least resistance such as the eyes, the membranous area of transition between the head and thorax (neck) or between thorax and abdomen, or between the last abdominal tergites. Puncture is followed by the injection of saliva, whose active components perform two functions: neurotoxins cause paralysis of the victim, while proteolytic enzymes lead to the breakup and liquefaction of internal tissues. In a short time, the predator is able to feed by sucking the internal fluids through the alimentary canal.
With regards to interspecific trophic relationships, a large number of reports exists on the prey captured by the Asilidae. Lavigne (2003) has developed a database comprising over 13,000 reports.[8] The prey of Asilidae are predominantly represented by other insects, mostly winged, but several cases in which they have attacked spiders have also been reported. Within the insects, orders that include the most frequent prey of asilids include a wide range of families within the Coleoptera, Hymenoptera, other Diptera, Hemiptera, and Lepidoptera; prey belonging to various other orders (Odonata, Neuroptera, Isoptera, Thysanoptera, Blattodea, etc.) are also mentioned.
With regards to the specificity of the trophic relationship, Wood (1981)[2] mentions some studies in the literature on the subject. Some genera have been found to be monophagic, but more generally Asilidae are polyphagic, with behaviors that vary from narrow specialization[8] to broad prey choice.[2]
Other studies[9] have shown that the ratio between the size of the prey and the asilid varies from 1.8:1 to 3.7:1, with an average of 2.6:1. The ratio tends to increase with decreasing size of the predator.
Didysmachus picipes lays eggs on an ear of grass
Egg-laying takes place, according to the species, with three different behaviors that relate to the structure and the morphology of the abdomen. Females with an undifferentiated ovipositor release eggs randomly and independently from the substrate. In other cases, however, the abdomen bears a differentiated, specialized ovipositor to lay eggs in the soil or sand, or lay them in cavities within plant tissues.
Habitat and ecology
Asilidae generally occur in habitats that are open, sunny, and dry, even arid. They favour open or scattered vegetation, and some species even frequent bare ground. Typical habitats include savannah, forest steppe, open steppe, semidesert, maquis shrubland, and related shrubland types such as fynbos and chaparral. Their biodiversity is lower in forested ecosystems, and where asilids do occur in such environments, they tend to concentrate in the glades and margins. In those conditions, the interrupted canopy leaves space for various species of shrubs and herbaceous plants suited to asilid styles of predation.
In general, the biology of the Asilidae is still poorly known, but various authors have studied the population distribution in particular regions and ecosystems. They have classified the behavioral patterns in terms of microenvironments, ecological, and trophic factors, showing how different species of Asilidae favour particular habitats suited to particular patterns of reproduction and predation. Specific studies show correlations between the floristic composition and predatory behaviour. [10]
Asilidae Robber fly from the Anaimalai hills, Western Ghats, India
Asilidae occur in all zoogeographical regions except Antarctica. In the Northern Hemisphere, some species are even adapted to tundra. Alpine species occur at altitudes exceeding 4000 meters/13,000 feet. However, the highest levels of biodiversity are in warm climates; tropical or subtropical and arid or semi-arid regions tend to have the greatest variety of species, followed by areas where rainfall is highly seasonal.
Systematics
Female Stenopogon martini feeding on a honeybee
The Asilidae currently include over 7500 described species in about 556 genera.[11] Their taxonomy is still under study in the light of new specimens and cladistic analysis. The 14 accepted subfamilies are:[12]
Carl Linnaeus (Linné; 1758), in the 10th edition of Systema Naturae, erected the genus Asilus, including 11 species, and added four others in the 12th edition (1767). Asilus crabroniformis (1758) is the type of the genus. The rank of family is credited to Leach in Samouelle (1819). Johan Christian Fabricius in five publications dated from 1775 to 1805, erected the genus Damalis and described 76 exotic and European species. Wiedemann, in publications appearing between 1817 and 1830, described 235 species, many exotic. Johann Wilhelm Meigen in an early work of 1803 erected four genera, three of which now represent subfamilies. He also described many species in Systematische Beschreibung der bekannten europäischen zweiflügeligen Insekten (1800 to 1838). During the rest of the 19th century, significant contributions were made by Hermann Loew in particular. Other prominent authors dealing with the Asilidae during the 19th century included Pierre-Justin-Marie Macquart, Francis Walker, Camillo Rondani, and Jacques-Marie-Frangile Bigot.
Flies are insects of the order Diptera, the name being derived from the Greek δι- di- "two", and πτερόν pteron "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced mechanosensory organs known as halteres, which act as high-speed sensors of rotational movement and allow dipterans to perform advanced aerobatics. Diptera is a large order containing an estimated 1,000,000 species including horse-flies, crane flies, hoverflies, mosquitoes and others, although only about 125,000 species have been described.
The Bombyliidae are a family of flies, commonly known as bee flies. Adults generally feed on nectar and pollen, some being important pollinators. Larvae are mostly parasitoids of other insects.
The Asiloidea comprise a very large superfamily insects in the order Diptera, the true flies. It has a cosmopolitan distribution, occurring worldwide. It includes the family Bombyliidae, the bee flies, which are parasitoids, and the Asilidae, the robber flies, which are predators of other insects.
The Phoridae are a family of small, hump-backed flies resembling fruit flies. Phorid flies can often be identified by their escape habit of running rapidly across a surface rather than taking to the wing. This behaviour is a source of one of their alternate names, scuttle fly. Another vernacular name, coffin fly, refers to Conicera tibialis. About 4,000 species are known in 230 genera. The most well-known species is cosmopolitan Megaselia scalaris. At 0.4 mm in length, the world's smallest fly is the phorid Euryplatea nanaknihali.
The Conopidae, also known as the thick-headed flies, are a family of flies within the Brachycera suborder of Diptera, and the sole member of the superfamily Conopoidea. Flies of the family Conopidae are distributed worldwide in all the biogeographic realms except for the poles and many of the Pacific islands. About 800 species in 47 genera are described worldwide, about 70 of which are found in North America. The majority of conopids are black and yellow, or black and white, and often strikingly resemble wasps, bees, or flies of the family Syrphidae, themselves notable bee mimics. A conopid is most frequently found at flowers, feeding on nectar with its proboscis, which is often long.
The Acroceridae are a small family of odd-looking flies. They have a hump-backed appearance with a strikingly small head, generally with a long proboscis for accessing nectar. They are rare and not widely known. The most frequently applied common names are small-headed flies or hunch-back flies. Many are bee or wasp mimics. Because they are parasitoids of spiders, they also are sometimes known as spider flies.
The Therevidae are a family of flies of the superfamily Asiloidea commonly known as stiletto flies. The family contains about 1,600 described species worldwide, most diverse in arid and semiarid regions with sandy soils. The larvae are predators of insect larvae in soil.
The Agromyzidae are a family of flies, commonly referred to as the leaf-miner flies for the feeding habits of their larvae, most of which are leaf miners on various plants. It includes roughly 2,500 species, they are small, some with wing length of 1 mm. The maximum size is 6.5 mm. Most species are in the range of 2 to 3 mm.
The Scenopinidae or window flies are a small family of flies (Diptera), distributed worldwide. In buildings, they are often taken at windows, hence the common name window flies.
Empis tessellata is a species of dance fly, in the fly family Empididae. It is included in the subgenus Euempis.
Dipteran morphology differs in some significant ways from the broader morphology of insects. The Diptera is a very large and diverse order of mostly small to medium-sized insects. They have prominent compound eyes on a mobile head, and one pair of functional, membraneous wings, which are attached to a complex mesothorax. The second pair of wings, on the metathorax, are reduced to halteres. The order's fundamental peculiarity is its remarkable specialization in terms of wing shape and the morpho-anatomical adaptation of the thorax – features which lend particular agility to its flying forms. The filiform, stylate or aristate antennae correlate with the Nematocera, Brachycera and Cyclorrhapha taxa respectively. It displays substantial morphological uniformity in lower taxa, especially at the level of genus or species. The configuration of integumental bristles is of fundamental importance in their taxonomy, as is wing venation. It displays a complete metamorphosis, or holometabolous development. The larvae are legless, and have head capsules with mandibulate mouthparts in the Nematocera. The larvae of "higher flies" (Brachycera) are however headless and wormlike, and display only three instars. Pupae are obtect in the Nematocera, or coarcate in Brachycera.
Diptera is an order of winged insects commonly known as flies. Diptera, which are one of the most successful groups of organisms on Earth, are very diverse biologically. None are truly marine but they occupy virtually every terrestrial niche. Many have co-evolved in association with plants and animals. The Diptera are a very significant group in the decomposition and degeneration of plant and animal matter, are instrumental in the breakdown and release of nutrients back into the soil, and whose larvae supplement the diet of higher agrarian organisms. They are also an important component in food chains.
Prolepsis is an insect genus of mainly neotropical Diptera in the family Asilidae or robber flies.
Diogmites is a genus of mainly neotropical flies in the family Asilidae or robber flies.
Neoitamus cyanurus, the common awl robberfly, is a species of 'robber fly' belonging to the family Asilidae.
Philonicus albiceps is a species of 'robber fly' belonging to the family Asilidae. It is a Palearctic species with a limited distribution in Europe
Neoitamus melanopogon, commonly known by the name common robber fly, is a species of fly of Asilidae in the genus Neoitamus, found in both the principal islands of New Zealand.
Mallophora bomboides, also known as the Florida bee killer, is a predaceous species of robber fly of the family Asilidae that feeds primarily on bumblebees. M. bomboides is a noteworthy instance of Batesian mimicry given its close resemblance to its prey, the bumblebee. These bees are typically found in the Eastern and Southern regions of the United States like South Carolina and Florida.
Mallophora ruficauda is a species of parasitic robber fly in the family Asilidae, endemic to South and Central America. Like other robber flies, M. ruficauda is known for its aggressive behavior and predation upon other insects, especially bees. M. ruficauda mimics a bumblebee to fool predators into thinking it has a painful sting and is not worth eating.
Hyperechia is a genus of robber flies in the family Asilidae. They appear large, stout and with legs covered in bristles and appear like carpenter bees in the genus Xylocopa and the resemblance is considered as a case of aggressive mimicry, providing protection from predators. The larvae of the fly feed on the larvae of Xylocopa within their cavity nests in wood. They are mainly found in the African and Madagascan region with about 15 species and two species in Asia.
1 2 3 Wood, Grace C. (1981). "Asilidae"(PDF). In McAlpine, J. F.; Peterson, B. V.; Shewell, G. E.; Teskey, H. J.; Vockeroth, J. R.; Wood, D. M. (eds.). Manual of Nearctic Diptera. Vol.1. Ottawa: Biosystematics Research Institute. pp.549–73. ISBN978-0-660-10731-8. Archived from the original(PDF) on 2016-11-04. Retrieved 2016-04-18.
1 2 Richards, O. W.; Davies, R. G. (1977). Imms' General Textbook of Entomology: Volume 1: Structure, Physiology and Development Volume 2: Classification and Biology. Berlin: Springer. ISBN978-0-412-61390-6.[pageneeded]
↑ Dennis, D Steve; Lavigne, Robert J (1975). Comparative behavior of Wyoming robber flies II (Diptera: Asilidae). Laramie: Agricultural Experiment Station, University of Wyoming. OCLC10795887.[pageneeded]
↑ Dennis, D. Steve; Barnes, Jeffrey K.; Knutson, Lloyd (17 June 2013). "Review and analysis of information on the biology and morphology of immature stages of robber flies (Diptera: Asilidae)". Zootaxa. 3673 (1): 1–64. doi:10.11646/zootaxa.3673.1.1. PMID26146701.
↑ D. Grimaldi. 1990. Insects from the Santana formation, Lower Cretaceous, of Brazil - Chapter 9. Diptera. Bulletin of the American Museum of Natural History195:164-183
Hull, Frank M. (1962). "Robber Flies of the World: The Genera of the Family Asilidae". Bulletin of the United States National Museum (224): 1–907. doi:10.5479/si.03629236.224. hdl:10088/10126.
Musso, Joseph-Jean (1978). Recherches sur le développement, la nutrition et l'écologie des Asilidae (Diptera - Brachycera)[Development research, nutrition and ecology of Asilidae (Diptera - Brachycera)] (PhD thesis) (in French). OCLC30534417.
Oldroyd, Harold (1969). Tabanoidea and Asiloidea. Handbooks for the identification of British insects. Royal Entomological Society. OCLC256410648.
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