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Camel Spiders

Solifugae

The solifugae is a distinctive order within the class Arachnida. They are also called camel spiders, sun spiders, scorpion carriers, wind scorpions, or solifuges. Despite their common names, these arachnids are not true spiders (order Araneae) or true scorpions (order Scorpiones). The term ‘solifugae’ is derived from the Latin words ‘sol’ and ‘fugere,’ which roughly translates to ‘sun’ and ‘to flee’ or ‘to escape.’ 

Although found worldwide, these solifugids predominantly inhabit arid environments, engaging in opportunistic predation on terrestrial arthropods and various small animals. Each camel spider has a striking appearance, with the body of a hairy spider and a face with jaws or ‘chelicerae’ resembling a crab’s pincers. The size of most Solifugae species extends from 12 to 15 cm (5 to 6 inches), including the legs.

Over 1,200 described species of camel spiders are distributed under 16 families and 146 genera, many of which are still under study.

Description

Most camel spiders are moderately small to large, with the largest species usually attaining an overall body length of 12 to 15 cm (5 to 6 inches), including their legs. However, this measurement can vary due to differences in leg length across different species. A more accurate depiction of their size is thus obtained by considering the body length alone, which can extend up to 7 cm (approximately 3 inches), although most species measure even close to 5 cm (2 inches). In contrast, some smaller species measure less than 1 cm (0.4 inches) at maturity.

Their body plan mirrors that of the spiders (Araneae), being divided into two primary tagmata: the anterior ‘prosoma’ (cephalothorax) and the posterior ‘opisthosoma’ (10-segmented abdomen). However, unlike spiders, these two tagmata are not separated by a pedicel (connecting tube), thus implicating the evolutionary divergence between Solifugae and Araneae.

The prosoma comprises the head, mouthparts, and somites that bear the legs and pedipalps and is encased by a carapace, also called a prosomal dorsal shield or ‘peltidium.’ The carapace is divided into three distinct segments: the propeltidium, mesopeltidium, and metapeltidium. The propeltidium houses the eyes, conspicuously large chelicerae (for feeding), pedipalps (for sensory reception), and the first two pairs of legs. The meso- and metapeltidium segments accommodate the remaining leg pairs. Unlike scorpions, camel spiders lack the third tagma that usually forms a tail.

Chelicerae

These jaw-like mouth parts stand out as one of the most striking features of camel spiders, justifying their classification under the subphylum Chelicerata. These chelicerae are bifurcated into two articles or segments (parts connected by joints), culminating in a powerful pincer, as found in crabs. Depending on the species, these articles bear a variable number of teeth for feeding.

Pedipals and Legs

They possess five pairs of legs, but only the posterior four pairs constitute true legs, each segmented into seven parts: coxa, trochanter, femur, patella, tibia, metatarsus, and tarsus. The first pair of appendages, often mistaken for legs, are actually ‘pedipalps’ and have five segments each. The first pair of true legs are smaller and thinner than the three posterior pairs, supplementing the pedipalps in tactile reception. Primarily, the posterior three pairs of legs are used in locomotion. The camel spiders feature specialized sensory structures called ‘malleoli’ or ‘racquet organs’ on the ventral surfaces of the coxae and trochanters of the last pair of legs.

Sexual dimorphism is prominent in them, with the males having smaller body sizes but proportionally longer legs than the females. Another distinctive characteristic of males is the presence of a pair of flagella (also called horns) on each chelicera, which are believed to have a reproductive significance. However, their exact function is yet to be discovered.

Eyes

They have prominently large central eyes resembling ocelli (simple eyes) but are significantly more developed to hunt and avoid enemies. This development might indicate an advanced evolutionary stage during the transition from a cluster of simple ocelli to a more integrated, singular compound eye structure.

Physiology

Unlike most arachnids from the orders of scorpions and Tetrapulmonata, Solifugae do not possess book lungs. Instead, they feature an advanced tracheal system for respiration, drawing in and expelling air through multiple spiracles. Specifically, they have one pair of spiracles between the second and third pairs of walking legs, two pairs situated on the third and fourth abdominal segments, and a single, unpaired spiracle on the fifth abdominal segment. Solifugae exhibits opisthosomal protuberances resembling the pulmonary sacs observed in certain palpigrades – a group of minute, enigmatic arachnids known for their distinct respiratory structures during embryonic development.

Taxonomy

In 2023, a groundbreaking phylogenomics study provided a clear picture of Solifugae’s family tree, showing two primary branches or suborders: Boreosolifugae and Australosolifugae. Daesiidae and Ammotrechidae were recovered monophyletic as the family Melanoblossidae was found nested within Daesiidae, and the family Mummuciidae was found nested within Ammotrechidae. 

This nuanced phylogenetic classification and the geographical distribution of camel spider families across the two hemispheres support the theory that states that Australosolifugae likely came from Gondwana, a southern supercontinent, while the Boreosolifugae from Laurasia, a northern supercontinent.

According to the World Solifugae Catalog, camel spiders are distributed under the following suborders and families.

Types of Camel Sun Spiders Wind Scorpion

Distribution

These arachnids are primarily found in arid and semiarid regions, including Africa’s Sahara desert, the Sonoran and Mojave Deserts of North America, the Arabian Peninsula of Asia, and the Middle East, except Antarctica and Australia.

Habitat

They usually thrive in sandy habitats with high temperatures, low humidity, and minimal vegetation. Although considered endemic to desert biomes, they also inhabit semi-deserts, grasslands, scrubs, and forests.

Diet

Camel spiders are opportunistic feeders that primarily consume arthropods, such as termites and darkling beetles, and some mammals, like large slit-faced bats and rodents. Sometimes, they also hunt snakes, small lizards, and birds.

Behavior

Lifespan

Camel spiders typically have a short lifespan and survive about one or two years.

Reproduction and Life Cycle

These animals are univoltine, reproducing only once a year. The males and females gather during mating, and reproduction occurs either by direct or indirect sperm transfer.

In families like Galeodidae, the males use specialized structures called ‘modified palps’ or ‘embolus’ to transfer sperm directly into the female’s genital opening. Whereas, in families like Solpugidae, sperm transfer takes place indirectly, where the male deposits a spermatophore (capsule containing sperm) on the ground and guides the female to pick it up using her gonopods (appendages specialized for reproduction). The female later uses the stored sperm to fertilize her eggs while laying them.

About 50 to 200 eggs are laid and stored in burrows dug by the mother for protection against predators. She cautiously guards her eggs until they are ready to hatch in a few weeks. This young spider goes through 9 to 10 growth stages, known as instars, during which it repeatedly sheds its outer layer, or exoskeleton until it reaches adulthood.

Predators

They are preyed upon by large slit-faced bats, scorpions, toads, and large spiders. In addition to these natural predators, humans pose a significant threat to camel spiders by destroying their habitats and thus reducing their numbers.

Adaptations

References Article last updated on 30th March 2024
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