Camel spider

The camel spider belongs to the order Solifugae of the class Arachnida. It is related to both spiders and scorpions but it is not a scorpion and not a spider. The presented phylogenetic tree (further down) indicates how solifugids such as camel spiders share the same common ancestor as spiders and scorpions.

The Greeks were the first to recognize Camel Spiders as an individual group and named them phalangium because of what appears as five legs¹. However, solphugids diverged from the other arthropods several hundred million years ago and they are really different as e.g. their breathing system is derived from that of insects². This allows a relatively fast oxygen consumption when needed and hence the possibilty of moving fast.

Through the ages, camel spiders have been given many names such as sun spiders, beard cutters (due to their large jaws), wind spiders, wind scorpions and many other names. They pose no threat to humans but due to their appearance and the many myths about them their popularity is unquestioned.

The name solifugid means « escaping from the sun » which is very characteristic of the camel spider. Camel spiders prefer dry, sandy areas as they are found in Northern Africa and in the Middle East.

The hissing sound they can generate also adds to the myths. The hissing sound is made by something called a stridulatory organ.

A recent study showed that the stridulatory organ had a similar morphology in all developmental stages of the camel spider³.

One of the conclusion from the study was that the hissing only had a defensive function (ibid).

Camel spider

The myth about their size, such as the one that they can grew as large as a dinner plate, gets stronger because of pictures such as the one below. The picture is a hoax and shows two camel spiders tied together (something scorpions also do).

Habitat - fleeing from the sun

Solifugids, like camel spiders, prefer shade and are mostly nocturnal. Some have said that they actually chase people in the desert of Iraq. Of course it is rather the shadow that is chased.

Diet

Camel spiders are carnivores and eats a variety of animals that it can kill with its strong chelicerae. Its diet includes small rodents, spiders, insects, termites, and small lizards. They are not strong enough to capture and kill large mammals, but occasionally they capture small birds.

Hunting

Camel spiders can run at a speed of up to 10 miles per hour. They have a very high metabolic rate which is part of the reason why they can reach such a high speed. Their life-span is shorter than that of scorpions which may be due to their higher metabolism.

Appearance

Camel spiders can reach a length of 5 inches when stretched out. Most camel spiders doesn't reach that size and the normal size is somewhere between ½-3 inches. Their abdomen have eleven segments and there is no segment separating the head from the abdomen. They have two clearly visible eyes and five so called racket organs. These are probably rudimentary eyes as many scorpions have five very small eyes.

Camel spiders are covered with hairs and spines that help them move fast and sense vibrations in their surroundings.

Mating behavior

In his study from 1966, Martin Huma⁴ divides the mating habits of solpugids into three phases. The first phase is the attack phase; the second phase is the contact phase and the third phase, the transfer phase. In the first phase, the attack phase, either the male or female assumes an attack position by raising the first pair of legs. In this phase the male might initiate the contact phase by a jump forward towards the female. This either results in a combat between the two, or a submission by the female, where the male grabs her with his chelicerae. If she doesn't fight him so much that he flees, the male with copulate with the female to produce offspring with her.

Systematics of Arachnids

The solifugae order and its evolution

The Solifugae is a distinct evolutionary lineage. The first Solifugae probably evolved in the Mesozoic Era around 250-65 Million years ago as an ancestor of some primordal scorpion from the sea. The picture above shows how camel spiders are related to both scorpions and true spiders. It is obvious that they are closer related to scorpions.

Arachnida consist of 10 orders (see below) of which the camel spiders (Solifugae) is one of them. Within the Camel spiders there are approx. 900 species in six different families.

Table: Various orders within the Class Arachnida

Acari	Mites and ticks
Araneae	True spiders
Opiliones	Harvestmen
Palpigradi	Micro-whip scorpions
Pedipalpi	Whip Scorpions
Pseudoscorpiones	Pseudoscorpions
Ricinulei	Ricinulids
Scorpiones	Scorpions
Solifugae	Camel Spiders

Camel spiders vs. spiders and scorpions

Although camel spiders look similar to spiders and scorpions, they are different. They neither have venom nor silk glands and they kill and chew their prey with their powerful jaws.

References

¹ Fred Punzo, The biology of camel-spiders (Arachnida, Solifugae) (1998)
² Lighton & Fielden, Gas Exchange in Wind Spiders (Arachnida, Solphugidae): Independent Evolution of Convergent Control Strategies in Solphugids and Insects. J. of Insect Physiol Vol 42(4), pp 347-357 (1996)
³ Hruskova-Martisova et al., Analysis of the stridulation in solifuges (Arachnida : Solifugae). J. of insects behavior 21(5) pp. 440-449 (2008)
⁴ Muma, Martin H., MATING BEHAVIOUR IN THE SOLPUGID GENUS EREMOBATES BANKS. J. of i 14(2-3) pp. 346-350 (1966)

Acknowledgements

Thanks to James, Mayra and John for giving me the permission to use their photos.

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