Solifugae
Template:Short description Template:Automatic taxobox 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 their common names, they differ from both order Araneae (spiders) and order Scorpiones (scorpions). Most species of solifuges live in dry climates and feed opportunistically on ground-dwelling arthropods and other small animals. The largest species grow to a length of Template:Convert, including legs. A number of urban legends exaggerate the size and speed of solifuges, and their potential danger to humans, which is negligible.
Etymology
The order's name is derived from the Latin sol meaning "sun" and fugere meaning "to flee". Put together, it means "those that flee from the sun".<ref name=":02">Template:Cite web</ref> These animals have a number of common names, including sun spiders, wind scorpions, wind spiders, red romans, and camel spiders.<ref name=":02" /> In Afrikaans, they are known as haarskeerders ("hair shavers"), and baardskeerders ("beard shavers"), in reference to myths that they cut hair to be used as nest bedding.<ref name=":02" />
Anatomy
Solifuges are moderately small to large arachnids (a few millimeters to several centimeters in body length), with the larger species reaching Template:Convert in length, including legs.<ref name="geographic">Template:Cite web</ref><ref name="schmidt93">Template:Cite book</ref> 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 Template:Convert.<ref name=" Pech">Template:Cite book</ref><ref>Template:Cite book</ref> Most species are closer to Template:Convert long, and some small species are under Template:Convert in head-plus-body length when mature.<ref name="Punzo2" />
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.Template:Efn 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.<ref name="Punzo2" /> As can be seen, the solifuge prosoma and opisthosoma are not separated by nearly as clear a constriction and connecting tube or "pedicel" as occurs in the Araneae (spiders). The lack of the pedicel reflects another difference between the Solifugae and spiders, namely that solifuges lack both spinnerets and silk, and as a consequence cannot spin webs. Spiders need considerable mobility of their abdomens in their spinning activities, and the Solifugae have no need for such an 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. The meso- and metapeltidium contain the third and fourth pairs of legs.<ref name="Punzo2" /><ref name="Dunlop et al. 2012">Template:Cite journal</ref><ref name=IZ>Template:Cite book</ref> 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".
Solifuges have a pair of large central eyes known as median ocelli.<ref name="Punzo2" />Template:Rp These eyes are oriented at the very front of its cephalothorax and are placed closely together.<ref name=":42">Template:Cite book</ref>Template:Rp The eyes have a pigment-cup structure and are covered by a domed outer lens made from the animal's exoskeleton.<ref name="Punzo2" />Template:Rp Below the dome is the animal's retina, a multi-tiered structure with a layer of cells called the vitreous body at its top. 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. Interspersed between the rhabdomeres are pigment cells. The eye's optic nerve begins at its center and is connected to the axons of numerous rhabdomeres.<ref name="Punzo2">Template:Cite book</ref>Template:Rp
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. These ocelli's lenses are usually atrophied. However, in some species both nerves and pigment cells are present. In species where lateral eyes are functional, they probably aid in detecting motion or changes in brightness.<ref name="Punzo2" />Template:Rp
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Like other arachnids outside the orders of scorpions and the Tetrapulmonata, the Solifugae lack book lungs, instead possessing 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.<ref name="Ax 2000">Template:Cite book</ref> 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.<ref>Template:Cite journal</ref> As embryos they also have opisthosomal protuberances resembling the pulmonary sacs found in some palpigrades.<ref name="Ballesteros et al 2019">Template:Cite journal</ref> They utilize discontinuous gas exchange almost identical to that of insects, where they go through periods where the spiracles are closed, followed by a phase with open spiracles to allow gas exchange.<ref>Template:Cite journal</ref>
Solifuges are somewhat sexually dimorphic, with the smaller males often possessing longer legs.<ref name=schmidt93/> Furthermore, the males bear a pair of flagella, one on each chelicerae, which are visible near the tip of each chelicerae. 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.<ref name="ISBN 978-0-7993-4689-3"/>
Chelicerae
Template:Main Template:Multiple image Among the most distinctive features of the Solifugae are their large chelicerae, which in many species are longer than the rest of the prosoma. Each of the two chelicerae has two articles (segments; parts connected by a joint),<ref name="isbn0-19-861271-0">Template:Cite book</ref> forming a powerful pincer, much like that of a crab; each article bears a variable number of teeth, largely depending on the species.<ref name="Punzo2" /><ref name=IZ/> 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.<ref name="ISBN 978-0-7993-4689-3">Template:Cite book</ref> Many Solifugae stridulate with their chelicerae, producing a rattling noise.<ref name=schmidt93/>
Other appendages
Template:Further The legs and pedipalps of solifuges work the same way as in most other arachnids. Although the Solifugae appear to have five pairs of legs, only the four posterior (hindmost) pairs are considered true legs. Each true leg has seven segments: the coxa, trochanter, femur, patella, tibia, metatarsus, and tarsus.<ref name="ISBN 978-0-7993-4689-3"/><ref name="Filmer">Template:Cite book</ref>
The first or anterior pair 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.<ref>A sticky situation: Solifugids (Arachnida, Solifugae) use adhesive organs on their pedipalps for prey capture</ref><ref name="ISBN 978-0-7993-4689-3" /><ref name="CNH">Harmer, Sir Sidney Frederic; Shipley, Arthur Everett et alia: The Cambridge natural history Volume 4, Crustacea, Trilobites, Arachnida, Tardigrada, Pentastomida etc. Macmillan Company 1895</ref> For the most part, only the posterior three pairs of legs are used for running.<ref name=IZ/><ref name="ISBN 978-0-7993-4689-3"/>
On the ventral portion (undersides) of the coxae and trochanters of the last pair of legs, the Solifugae possess fan-shaped structures called malleoli, also referred to as the racket organs (Template:Singular malleolus). These paired organs are chemoreceptors,<ref>Template:Citation</ref> being the analogues of pectines in scorpions, and modified walking limbs in the uropygids and amblypygids as well as the pedipalps in spiders and other arachnids.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Generally, solifuges have five pairs of malleoli on the ventral surface of the fourth pair of legs. Malleoli are usually larger in males.<ref>Template:Cite journal</ref> 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.Template:Citation needed Sometimes, the blades of the malleoli are directed forward, sometimes not.<ref name="ISBN 978-0-7993-4689-3"/><ref name="Punzo2" />Template:Rp
Habitat and distribution
Most solifuges live in tropics and subtropical deserts in the Americas, Southern Europe, Africa, the Middle East, and South Asia. Surprisingly, these animals are absent in Australia and Madagascar.<ref name="Punzo2" />Template:Rp Within the desert, solifuges live in a variety of micro-habitats. These include sand dunes, sand flats, floodplains, rocky hillsides, desert shrublands, gravel plains, and mountain valleys.<ref name="Punzo2" />Template:Rp In addition to the desert, certain solifuges live in more arid grasslands and forests.<ref name="Punzo2" />Template:Rp
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 on the surface, occasionally seeking refuge in cracks or under rocks and vegetation.<ref name="Punzo2" />Template:Rp
Behavior and life history
Diet and hunting
Solifuges are carnivores and typically generalists, feeding on a wide variety of prey in their given environment.<ref name="Punzo2" />Template:Rp For most species, insects make up the bulk of their diet.<ref name="Punzo2" />Template:Rp However, these animals have been known to consume anything they can subdue.<ref name="Punzo2" />Template:Rp This includes other arachnids like spiders, scorpions, and smaller solifuges, other arthropods like millipedes, and small lizards, birds, and mammals.<ref name="Punzo2" />Template:Rp Additionally, solifuges are voracious eaters. It's common for adult females to eat so much that they're temporarily unable to walk.<ref name="Punzo2" />Template:Rp
When looking for prey, most solifuges rapidly move around while tapping their pedipalps on the ground.<ref name="Punzo2" />Template:Rp The only exception is the majority of termite-loving species, as they prefer to be more sedentary.<ref name="Punzo2" />Template:Rp 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.<ref name="Punzo2" />Template:Rp How much the animal relies on each sense depends on the species.<ref name="Punzo2" />Template:Rp While all hunt on the ground, some species are great climbers, able to search for prey on trees, shrubs, and on artificial structures.<ref name="Punzo2" />Template:Rp
Solifuges hunt their prey using three main hunting-strategies: Stalking, chasing, and ambushing.<ref name="Punzo2" />Template:Rp Depending on the meal's size, prey is seized with the animal's pedipalps or massive chelicerae.<ref name="Punzo2" />Template:Rp When the pedipalps are used, prey is initially caught with the limb's suction cups, then rapidly pulled toward the chelicerae to be chewed.<ref name="Punzo2" />Template:Rp These motions happen so fast that they can't be distinguished.<ref name="Punzo2" />Template:Rp 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).<ref name="Punzo2" />Template:Rp
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.<ref name="Punzo2" />Template:Rp This chewing motion turns the food into a liquidized paste which is then swallowed by the animal's pharynx.<ref name="Punzo2" />Template:Rp Solifuges that haven't fed for long periods are known to eat faster than ones that fed recently.<ref name="Punzo2" />Template:Rp Larger solifuges are also known to eat faster than smaller ones.<ref name="Punzo2" />Template:Rp
Reproduction
The Solifugae are typically univoltine (reproducing once a year).<ref name="Punzo">Template:Cite book</ref>Template:Rp 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 Template:Convert has been observed to eat more than 100 flies during that time in the laboratory.<ref name=schmidt93/> The Solifugae undergo a number of stages including, egg, postembryo, 9–10 nymphal instars, and adults.<ref name="Punzo"/>
Diapause
Solifuges undergo periods of diapause (variously referred to as dormancy,<ref name="Seasonal">Belozerov VN. Seasonal aspects of life cycles of solifuges (Arachnida, Solifugae) and their comparison with pseudoscorpions (Arachnida, Pseudoscorpiones) Entomological Review 2013; 92: 416–48 [1] </ref> torpor,<ref>Muma MH. Basic behavior of North American Solpugida . The Florida Entomologist 1967; 50: 115–23 [2] </ref> or hibernation<ref name="Adaptational">Template:Cite journal </ref><ref>Phan, F. Hibernation en captivite d'un solifuge marocain (Hibernation of the Moroccan solifuge in captivity) Arachnides 34:18 1997 Accession: 038301633 </ref>) in times such as during "unseasonable conditions" unsuitable for them (such as high rainfall or cold temperatures).<ref name="Seasonal"/> Solifuges exhibit several types of voltinism, with annual, biannual, and multi-annual (semi-voltine) lifecycles having been observed.<ref name="Seasonal"/> Despite multiple references to this behavior, this behavior of dormancy, like many aspects of Solifugae, remain understudied and requires further systematic studies.<ref name="ScienceGuide">Template:Cite journal</ref>
Classification and phylogeny
Solifuges are an order of arachnids comprising over 1200 species in 146 genera assigned to 16 different families.<ref name="NMBE">Template:Cite web</ref><ref name=":022">Template:Cite journal</ref> Solifuges can be divided into two groups of families which are recognized as distinct suborders.<ref name=":1" /> These are the Australosolifugae which live predominantly in the Southern Hemisphere and the Boreosolifugae which live mostly in the Northern Hemisphere.<ref name=":1" /> This phylogeny is considered congruent with a Gondwanan origin for Australosolifugae and a Laurasian origin for Boreosolifugae.<ref name=":1">Template:Cite journal</ref> When looking at their relationships, the families Ammotrechidae and Daesiidae were found to be paraphyletic, leading to multiple clades without a name.<ref name=":1" /> Because of this, a later genomic study established three additional families: Dinorhaxidae, Lipophagidae, and Namibesiidae.<ref name=":022" /> Template:Columns-list
Phylogeny
Below is a family tree of the various solifuge families based on phylogenomics.<ref name="NMBE" /><ref name=":022" />
Relationship with humans
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).<ref>Template:Cite web—where they are called "four-jawed spiders".</ref> Anton August Heinrich Lichtenstein theorized in 1797 that the "mice" that plagued the Philistines in the Old Testament were Solifugae.Template:Citation needed During World War I, troopsTemplate:Clarify 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.<ref name="Punzo2" />Template:Rp
Urban legends
Template:Expand section 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 Template:Convert.<ref name=schmidt93/> They are fast on land compared to other invertebrates, with their top speed estimated to be Template:Convert.<ref name="geographic" />
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).<ref name="Klann 2009">Template:Cite thesis</ref> 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.<ref>Template:Cite journal</ref> 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.<ref name="Klann 2009" />
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.<ref>Template:Cite news</ref> An Arizona resident developed painful lesions due to a claimed solifuge bite but could not produce a specimen for confirmation.<ref>Template:Cite news</ref> Though they are not venomous, the powerful chelicerae of a large specimen may inflict a painful nip, but nothing medically significant.<ref>Template:Cite book</ref>
Claims that Solifugae aggressively chase people are also untrue, as they are merely trying to stay in the shade/shadow provided by the human.<ref>Template:Cite news</ref>
Footnotes
References
Further reading
- Babu, K. 1965. Anatomy of the central nervous system of arachnids. Zoologische Jahrbücher, Anatomie und Ontogenie 82: 1–154.
- Bernard, H. M. 1896. The comparative morphology of the Galeodidae. Transactions of the Linnean Society. 2d Series. Zoology 6: 305–417.*Brownell, P. H. and R. D. Farley. 1974. The organization of the malleolar sensory system in the solpugid, Chanbria sp. Tissue & Cell 6: 471–485. CrossRef, PubMed
- Harvey, M. S. 2003. Catalogue of the Smaller Arachnid Orders of the World. CSIRO Publishing, Collingwood Victoria, Australia.
- Koç, H. 2007. The solifuges (Arachnida: Solpugida) fauna of southeast Anatolia: systematic zoogeography and ecology, PhD thesis, Ege University, İzmir, 241 pp. [in Turkish]
- Template:Cite journal
- Punzo, F. 1998. The Biology of Camel-spiders (Arachnida, Solifugae). Kluwer Academic Publishers, Boston, MA. 301 pp. CrossRef
- Ruhlemann, H. 1908. Uber die Facherorgane, sog. Malleoli oder Raquettes coxales, des vierten Beinpaares der Solpugiden. Zeitschrift fr wissenschaftliche Zoologie 91: 599–639.
- Nazife Yiğit, Melek Erdek, Halil Koç, and Abdullah Melekoğlu. 2011. Morphological Comparison of the Malleoli (Racquet Organs) in Biton zederbaueri and Gluviopsilla discolor (Daesiidae, Solifugae)
External links
- Template:Cite web
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- Template:Cite news
- Camel Spider Feeding by Stefan F. Wirth
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