Solifugae is an order of arachnids known variously as solifuges, sun spiders, camel spiders, and wind scorpions. The order includes more than 1,000 described species in about 147 genera. Despite the common names, they are neither true scorpions (order Scorpiones) nor true spiders (order Araneae). Because of this, it is less ambiguous to call them "solifuges". Most species of solifuge live in dry climates and feed opportunistically on ground-dwelling arthropods and other small animals. The largest species grow to a length of 12–15cm (5–6in), including legs. A number of urban legends exaggerate the size and speed of solifuges, and their potential danger to humans, which is negligible.
The order's name is derived from the Latin "sol" meaning "sun" and "fugere" meaning "to flee". Put together, it means "those who flee from the sun".[2] These animals have a number of common names including sun spiders, wind scorpions, wind spiders, red romans, and camel spiders.[2] In Afrikaans, they are known as "haarskeerders" ("hair cutters"), and "baardskeerders" ("beard cutters"). This is in reference to myths that they cut hair to be used as nest bedding.[2]
Anatomy and physiology
Ventral aspect of a solifuge, showing respiratory slots
Solifuges are moderately small to large arachnids (a few millimeters to several centimeters in body length), with the larger species reaching 12–15cm (5–6in) in length, including legs.[3][4] In practice, the respective lengths of the legs of various species differ greatly, so the resulting figures are often misleading. More practical measurements refer primarily to the body length, quoting leg lengths separately, if at all. The body length is up to 7cm (3in).[5][6] Most species are closer to 5cm (2in) long, and some small species are under 1cm (0.4in) in head-plus-body length when mature.[7]
Like that of spiders, the body plan of the Solifugae has two main tagmata: the prosoma, or cephalothorax, is the anterior tagma, and the 10-segmented abdomen, or opisthosoma, is the posterior tagma. The abdominal tergites and sternites are separated by large areas of intersegmental membranes, giving it a high degree of flexibility and ability to stretch considerably, which allows it to consume a large amount of food.[7] As shown in the illustrations, the solifuge prosoma and opisthosoma are not separated by nearly as clear a constriction and connecting tube or "pedicel" as occurs in Araneae. The lack of the pedicel reflects another difference between the Solifugae and spiders, namely that solifuges lack both spinnerets and silk, and do not spin webs. Spiders need considerable mobility of their abdomens in their spinning activities, and the Solifugae have no such adaptation.
The prosoma comprises the head, the mouthparts, and the somites that bear the legs and the pedipalps. It is covered by a carapace, also called a prosomal dorsal shield or peltidium, which is composed of three distinct elements called propeltidium, mesopeltidium and metapeltidium. The propeltidium contains the eyes, the chelicerae that, in most species, are conspicuously large, the pedipalps and the first two pairs of legs. Meso- and metapeltidium contains the third and fourth pairs of legs.[7][8][9] The chelicerae serve as jaws and in many species also are used for stridulation. Unlike scorpions, solifuges do not have a third tagma that forms a "tail".
Currently, neither fossil nor embryological evidence shows that arachnids ever had a separate thorax-like division, so the validity of the term cephalothorax, which means a fused cephalon, or head, and thorax, has been questioned. Also, arguments exist against use of "abdomen", as the opisthosoma of many arachnids contains organs atypical of an abdomen, such as a heart and respiratory organs.[10]
Like other arachnids outside the orders of scorpions and the Tetrapulmonata, the Solifugae lack book lungs, having instead a well-developed tracheal system that inhales and exhales air through a number of spiracles - one pair between the second and third pair of walking legs, two pairs on the abdomen on abdominal segments three and four, and an unpaired spiracle on the fifth abdominal segment.[11] Air sacs are attached to the branching tracheae, with tracheoles penetrating the epithelia of internal organs. Hemocyanin, a respiratory pigment common in the hemolymph of many arachnids and other arthropods, is absent.[12] As embryos they also have opisthosomal protuberances resembling the pulmonary sacs found in some palpigrades.[13]
Chelicerae
Chewing movement of the chelicerae in solifuges dorsal view (top) and side view (bottom)Lateral aspect of chelicera, showing teeth and cutting edge
Among the most distinctive features of the Solifugae are their large chelicerae, which in many species are longer than the prosoma. Each of the two chelicerae has two articles (segments, parts connected by a joint),[14] forming a powerful pincer, much like that of a crab; each article bears a variable number of teeth, largely depending on the species.[7][9] The chelicerae of many species are surprisingly strong; they are capable of shearing hair or feathers from vertebrate prey or carrion, and of cutting through skin and thin bones such as those of small birds.[15] Many Solifugae stridulate with their chelicerae, producing a rattling noise.[4]
Legs and pedipalps
Male solifuge in South African veld: Its flagella are visible near the tips of the chelicerae, looking like large, backward-curling bristles.
These elements work the same way as in most other arachnids. Although the Solifugae appear to have five pairs of legs, only the hind four pairs are true legs. Each true leg has seven segments: coxa, trochanter, femur, patella, tibia, metatarsus, and tarsus.[15][16]
The first, or anterior, of the five pairs of leg-like appendages are not "actual" legs, but pedipalps, and they have only five segments each. The pedipalps of the Solifugae function partly as sense organs similar to insects' antennae, and partly in locomotion, feeding, and fighting. In normal locomotion, they do not quite touch the ground, but are held out to detect obstacles and prey; in that attitude, they look particularly like an extra pair of legs or perhaps arms. Reflecting the great dependence of the Solifugae on their tactile senses, their anterior true legs commonly are smaller and thinner than the posterior three pairs. That smaller anterior pair acts largely in a sensory role as a supplement to the pedipalps, and in many species they accordingly lack tarsi. At the tips of their pedipalps, Solifugae bear a membranous suctorial organ, which are used for capturing prey, and also for bringing water to their mouthparts for drinking and climbing smooth surfaces.[17][15][18]
A female of a species in the family Solpugidae showing the malleoli beneath the posterior pair of legs
For the most part, only the posterior three pairs of legs are used for running.[9][15] On the undersides of the coxae and trochanters of the last pair of legs, the Solifugae have fan-shaped sensory organs called malleoli or racquet (or racket) organs. Sometimes, the blades of the malleoli are directed forward, sometimes not. They have been suspected to be sensory organs for the detection of vibrations in the soil, perhaps to detect threats and potential prey or mates.[15] These structures may be chemoreceptors.[7]:66
Males are usually smaller than females, with relatively longer legs.[4] Unlike females, the males bear a pair of flagella, one on each chelicera. In the accompanying photograph of a male solifuge, one flagellum is just visible near the tip of each chelicera. The flagella, which bend back over the chelicerae, are sometimes called horns and are believed to have some sexual connection, but their function has not yet been clearly explained.[15]
Eyes
Solifuge eyes with bristly setae
Solifuges have a pair of large central eyes known as median ocelli[7]:68 These eyes are oriented at the very front of its cephalothorax and are placed close together.[19]:68 These eyes have a pigment-cup structure and are covered by a domed outer lens made from the animal's exoskeleton.[7]:68–69 Below the dome is the animal's retina, a multi-tiered structure with a layer of cells called the vitreous body at its top.[7]:68 Underneath is the thin preretinal membrane, acting as a barrier between the vitreous body above and the rhabdomeres beneath. Rhabdomeres are light-sensitive and function as the eye's photoreceptors.[7]:68 Interspersed between the rhabdomeres are pigment cells.[7]:68 The eye's optic nerve begins at its center and is connected to the axons of numerous rhabdomeres.[7]:68
In addition to the median eyes, solifuges possess a pair of vestigial lateral ocelli. These eyes are found in pits on the animal's cephalic lobes near the chelicerae.[7]:68 The ocelli's lenses are usually atrophied. However, in some species both nerves and pigment cells are present.[7]:68 In species where lateral eyes are functional, they probably aid in detecting motions or changes in light intensity.[7]:68
Depending on the species in question, solifuges may be more sedentary or on the move. Sedentary species are often fossorial, living in relatively permanent burrows underground. Transitory species spend most of their time up the surface, occasionally seeking refuge in cracks or under rocks and vegetation.[7]:108
Solifuges are carnivores and typically generalists, feeding on a wide variety of prey in their given environment.[7]:131–132 For most species, insects make up the bulk of their diet.[7]:132 However, these animals have been known to consume anything they can subdue.[7]:132 This includes other arachnids like spiders, scorpions, and smaller solifuges, other arthropods like millipedes, and small lizards, birds, and mammals.[7]:132 Additionally, solifuges are voracious eaters. It's common for adult females to eat so much that they're temporarily unable to walk.[7]:132
When looking for prey, most solifuges rapidly move about while tapping their pedipalps on the ground.[7]:151 The only exception is the majority of termite-loving species, as they prefer to be more sedentary.[7]:151 In addition to using their pedipalps, solifuges have a variety of methods to locate prey. These include seeing movements with their eyes, feeling with their long hairlike setae, smelling with their malleoli, and sensing vibrations.[7]:151–152 How much the animal relies on each sense depends on the species.[7]:152 While all hunt on the ground, some species are great climbers, able to search for prey on trees, shrubs, and on artificial structures.[7]:156
Solifuges hunt their prey using three main hunting strategies: stalking, chasing, and ambushing.[7]:156 Depending on the meal's size, prey is seized with the animal's pedipalps or massive chelicerae.[7]:157 When the pedipalps are used, prey is initially caught with the limb's suction cups, then rapidly pulled towards the chelicerae to be chewed.[7]:158 These motions happen so fast that they can't be distinguished.[7]:158 Before eating, solifuges prepare their food by removing any parts they find unfavorable. In arthropods, these are typically areas that have a high amount of chitin (heads, antennae, wings, etc).[7]:164
Solifuges eat in different ways based on the shape of their food. Prey that is long and narrow is held perpendicular to the chelicerae and chewed from one end to another. More round prey is chewed by rotating the body all at once.[7]:158 This chewing motion turns the food into a liquidized paste which is then swallowed by the animal's pharynx.[7]:158 Solifuges that haven't fed for long periods are known to eat faster than ones that fed recently.[7]:161 Larger solifuges are also known to eat faster than smaller ones.[7]:161
Reproduction
The Solifugae are typically univoltine (reproducing once a year).[20]:8 Reproduction can involve direct or indirect sperm transfer; when indirect, the male emits a spermatophore on the ground and then inserts it with his chelicerae in the female's genital pore. To do this, he flings the female on her back.
The female then digs a burrow, into which she lays 50 to 200 eggs; some species then guard them until they hatch. Because the female does not feed during this time, she tries to fatten herself beforehand, and a species of 5cm (2.0in) has been observed to eat more than 100 flies during that time in the laboratory.[4] The Solifugae undergo a number of stages including, egg, postembryo, 9–10 nymphal instars, and adults.[20]
Solifuges have been recognized as distinct taxa from ancient times. In Aelian's De natura animalium, "four-jawed spiders" are credited, along with scorpions, as being responsible for the abandoning of a desert region near the Astaboras river (said to be in India, but thought to be a river in Ethiopia).[24]Anton August Heinrich Lichtenstein theorized in 1797 that the "mice" that plagued the Philistines in the Old Testament were Solifugae.[citation needed] During World War I, troops [clarification needed] stationed in Abū Qīr, Egypt, would stage fights between captive "jerrymanders", as they referred to them, and placed bets on the outcome. Similarly, British troops stationed in Libya in World War II staged fights between solifuges and scorpions.[7]:2–3
Urban legends
The Solifugae are the subject of many legends and exaggerations about their size, speed, behavior, appetite, and lethality. They are not especially large, the biggest having a leg span around 12cm (4.7in).[4] They are fast on land compared to other invertebrates, with their top speed estimated to be 16km/h (10mph).[3]
The Solifugae apparently have neither venom glands nor any venom-delivery apparatus such as the fangs of spiders, stings of wasps, or venomous setae of caterpillars (e.g., Lonomia or Acharia species).[25] One 1978 study is frequently quoted, in which the authors report detection of an exception in India, in that Rhagodes nigrocinctus had venom glands, and that injection of the secretion into mice was frequently fatal. However, no supporting studies have confirmed either statement, such as by independent detection of the glands as claimed, or the relevance of the observations, if correct. Even the authors of the original account admitted to having found no means of delivery of the putative venom by the animal, and the only means of administering the material to the mice was by parenteral injection.[26] Given that many non-venoms such as saliva, blood and glandular secretions can be lethal if injected, and that no venomous function was even speculated upon in this study, there is still no evidence for even one venomous species of solifuge.[25]
Because of their unfamiliar spider-like appearance and rapid movements, Solifugae have startled or even frightened many people. This fear was sufficient to drive a family from their home in August 2008 when one was allegedly discovered in a soldier's house in Colchester, England, and caused the family to blame the solifuge for the death of their pet dog.[27] An Arizona resident developed painful lesions due to a claimed solifuge bite but could not produce a specimen for confirmation.[28] Though they are not venomous, the powerful chelicerae of a large specimen may inflict a painful nip, but nothing medically significant.[29]
Claims that Solifugae aggressively chase people are also untrue, as they are merely trying to stay in the shade/shadow provided by the human.[30]
Related Research Articles
The subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids, as well as a number of extinct lineages, such as the eurypterids and chasmataspidids.
Arachnids are arthropods in the class Arachnida of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons.
Amblypygi is an order of arachnids also known as whip spiders or tailless whip scorpions, not to be confused with whip scorpions or vinegaroons that belong to the related order Thelyphonida. The name "amblypygid" means "blunt tail", a reference to a lack of the flagellum that is otherwise seen in whip scorpions. Amblypygids possess no silk glands or venom. They rarely bite if threatened but can grab fingers with their pedipalps, resulting in thornlike puncture injuries.
Schizomida, also known as sprickets or short-tailed whip-scorpions, is an order of arachnids, generally less than 5 millimetres (0.20 in) in length. The order is not yet widely studied. E. O. Wilson has identified schizomids as among the "groups of organisms that desperately need experts to work on them."
The Opiliones are an order of arachnids, colloquially known as harvestmen, harvesters, harvest spiders, or daddy longlegs. As of July 2024, over 6,650 species of harvestmen have been discovered worldwide, although the total number of extant species may exceed 10,000. The order Opiliones includes five suborders: Cyphophthalmi, Eupnoi, Dyspnoi, Laniatores, and Tetrophthalmi, which were named in 2014.
Ricinulei is a small order of arachnids. Like most arachnids, they are predatory; eating small arthropods. They occur today in west-central Africa (Ricinoides) and the Americas from South America to as far north as Texas, where they either inhabit leaf-litter or caves. As of 2022, 103 extant species of ricinuleids have been described worldwide, all in the single family Ricinoididae. In older works they are sometimes referred to as Podogona. Due to their obscurity they do not have a proper common-name, though in academic literature they are occasionally referred to as hooded tickspiders.
Pedipalps are the secondary pair of forward appendages among chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to the chelicerae ("jaws") and anterior to the first pair of walking legs.
The chelicerae are the mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as "jaws", chelicerae may be shaped as either articulated fangs, or as a type of pincers. Some chelicerae, such as those found on nearly all spiders, are hollow and contain venom glands, used to inject venom into prey or a perceived threat. Both pseudoscorpions and harvestmen have additional structures on their chelicerae that are used for grooming. In Paratrechalea, males and females have shown to have a chelicerae dimorphism, because the chelicerae is used as a mating signal for females.
Pulmonoscorpius is an extinct genus of scorpion from the Mississippian of Scotland. It contains a single named species, Pulmonoscorpius kirktonensis. It was one of the largest scorpions to have ever lived, with the largest known individual having an estimated length exceeding 70 cm. Pulmonoscorpius retains several general arthropod features which are absent in modern scorpions, such as large lateral eyes and a lack of adaptations for a burrowing lifestyle. It was likely an active diurnal predator, and the presence of book lungs indicate that it was fully terrestrial.
The anatomy of spiders includes many characteristics shared with other arachnids. These characteristics include bodies divided into two tagmata, eight jointed legs, no wings or antennae, the presence of chelicerae and pedipalps, simple eyes, and an exoskeleton, which is periodically shed.
Opiliones are an order of arachnids and share many common characteristics with other arachnids. However, several differences separate harvestmen from other arachnid orders such as spiders. The bodies of opiliones are divided into two tagmata : the abdomen (opisthosoma) and the cephalothorax (prosoma). Unlike spiders, the juncture between the abdomen and cephalothorax is often poorly defined. Harvestmen have chelicerae, pedipalps and four pairs of legs. Harvestmen were traditionally thought to have two eyes, except in the case of eyeless species. Developmental genetic work has shown that living species retain up to six eyes, including one pair of rudimentary median eyes and one pair of rudimentary lateral eyes.
Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. As of December 2023, 1,100 species have been identified, with 166 genera. The term "tarantula" is usually used to describe members of the family Theraphosidae, although many other members of the same infraorder (Mygalomorphae) are commonly referred to as "tarantulas" or "false tarantulas". Some of the more common species have become popular in the exotic pet trade. Many New World species kept as pets have setae known as urticating hairs that can cause irritation to the skin, and in extreme cases, cause damage to the eyes.
Spiders are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species diversity among all orders of organisms. Spiders are found worldwide on every continent except Antarctica, and have become established in nearly every land habitat. As of September 2024, 52,309 spider species in 134 families have been recorded by taxonomists. However, there has been debate among scientists about how families should be classified, with over 20 different classifications proposed since 1900.
This glossary describes the terms used in formal descriptions of spiders; where applicable these terms are used in describing other arachnids.
Chelypus ('clawfoot') is a genus of slow-moving, burrowing sunspiders confined to the deserts and arid regions of Southern Africa.
A malleolus is a fan-shaped chemoreceptor or racquet organ, an array of which are carried in pairs on the ventral or undersides of Solpugidae. They are the counterpart of pectines in scorpions, and modified walking limbs in the uropygids and amblypygids as well as the pedipalps in spiders and other arachnids. Generally, solifuges have five pairs of malleoli on the ventral surface of the fourth pair of legs. Malleoli are usually larger in males. A malleolus comprises a basal stalk and a triangular fan, with epicuticular protrusions on each anterior face, and granular structures on each stalk, with undulate surfaces at each distal end.
Chanbria is a genus of camel spiders. It consists of four species found in the Sonoran Desert in Mexico and the southwestern United States.
Hemiscorpius lepturus is a species of scorpion in the family Hemiscorpiidae. It is found in deserts of the Middle East, especially in southern Iraq and Iran, where it is sometimes referred to as the "Gadim scorpion". These scorpions have long, thin tails and wide bodies and grow to 8 cm (3.1 in) in males and 5.5 cm (2.2 in) in females, allowing them to live in tight rock crevices. They are fairly solitary creatures. H. lepturus has mainly been studied to discover the components and effects of its venom, which is highly lethal and is responsible for most deaths due to scorpion sting in the Iran area. H. lepturus is the only scorpion not in the family Buthidae that is potentially lethal to humans; the Buthidae family is the largest and most abundant family of scorpions, containing many highly venomous species.
1 2 3 Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp.613–614. ISBN0-03-056747-5.
↑ Shultz, Stanley; Shultz, Marguerite (2009). The Tarantula Keeper's Guide. Hauppauge, New York: Barron's. p.23. ISBN978-0-7641-3885-0.
↑ Ax, Peter (2000). "Solifugae". Multicellular Animals: The Phylogenetic System of the Metazoa. Translated by Kinsey, S. Berlin: Springer. pp.125–126. ISBN9783662103968.
↑ Harmer, Sir Sidney Frederic; Shipley, Arthur Everett et alia: The Cambridge natural history Volume 4, Crustacea, Trilobites, Arachnida, Tardigrada, Pentastomida etc. Macmillan Company 1895
↑ Aruchami, M.; Sundara Rajulu, G. (1978). "An investigation on the poison glands and the nature of the venom of Rhagodes nigrocinctus (Solifugae: Arachnida)". Natl. Acad. Sci. Lett. 1: 191–192.
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