The Arachnid Order Solifugae




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Introduction: Physiology

This section contributed by Anja E. Klann
Ernst-Moritz-Arndt-University Greifswald, Germany

 The maintenance of an equal body temperature without an extreme water loss is the main problem facing all desert arthropods (Cloudsley-Thompson, 1991).  Solifuges seem to be unusually tolerant of heat and drought compared to other desert arachnids or insects.  For example, Galeodes granti is able to survive 49°C with a relative humidity below 10% for 24h (Cloudsley-Thompson, 1962).  Punzo (1994) studied the combined effects of temperature and relative humidity along an altitudinal gradient in specimens of Eremobates palpisetulosus.  Due to the sometimes unexpected high differences in temperature between favorable microenvironments (such as burrows and other kinds of retreats) and the soil surface (Cloudsley-Thompson, 1956), nocturnal solifugid species (and other desert arthropods as well) usually retreat to such microenvironments during the daytime, enabling them to maintain thermal homeostasis to a certain degree.  

Even though Cloudsley-Thompson (1961) showed that Galeodes arabs C. L. Koch has a low water loss by transpiration, and thus a high capacity for water conservation, it occasionally drank in captivity by chewing on wet acacia leaves with its chelicerae.  In nature, however, solifuges seem to obtain sufficient moisture from the body fluids of their prey.

Various authors have described the relatively rapid sprint speeds of many solifugid species (e. g., Heymons, 1902), which requires an efficient respiratory system.  Solifuges are characterized by an apomorphic, highly complex tracheal system with spiracles that allows for direct O2 provision and CO2 elimination.  Lighton and Fielden (1996) examined the gas exchange in Eremcosta titania and Eremobates sp. (Eremobatidae) from the Mojave desert of California and revealed that they utilize a discontinuous gas exchange (DGC), which is almost identical to that of insects.  The DGC in solifuges can be divided into three distinct phases. The C phase is characterized by closed spiracles, and prevents almost any external gas exchange.  Endotracheal hypoxia probably causes the termination of the C phase, which is followed by a largely diffusive phase characterized by tissue-level O2 uptake.  The accumulation of CO2 in the hemolymph resulting from the sealed C phase initiates the O phase when reaching the hypercapnic set-point.  

Punzo (1998) summarized the few physiological studies published so far on the respiratory system, temperature and moisture stress, and neurochemistry.  The physiology of solifuges is only scarcely studied and therefore merits much more attention.

Literature Cited:

Cloudsley-Thompson, J.L. 1956. Studies in diurnal rhythms. - VI. Bioclimatic observations in Tunisia and their significance in relation to the physiology of the fauna, especially woodlice, centipedes, scorpions and beetles. Annals and Magazine of Natural History (12) 9: 305-329. 1956

Cloudsley-Thompson, J. L. 1961b. Some aspects of the physiology and behavior of Galeodes arabs. Entomologia    
            experimentalis et applicata
, 4: 257-263.

Cloudsley-Thompson, J.L. 1962. Lethal temperatures of some desert arthropods and the mechanism of heat death.             Entomologia Experimentalis et Applicata 5: 270-280.

Cloudsley-Thompson,  J.L. 1991. Ecophysiology of desert arthoropods and reptiles. Springer-Verlag: Berlin.

Heymons, R. 1902. Biologische Beobachtungen an asiatischen Solifugen, nebst Beiträgen zur Systematik derselben.             Abhandlungen der Preussischen Akademie der Wissenschafen zu Berlin, 1902: Anhang 1 [pages?].

Lighton, J.R.B. and Feldon, L.J. 1996. Gas exchange in wind spiders (Arachnida, Solphugidae [sic]): independent             evolution of convergent control strategies in solphugids [sic] and insects. Journal of Insect Physiology 42: 347-             357.

Punzo, F. 994c. Intraspecific variation in response to temperature and moisture in Eremobates palpisetulosus Fichter             (Solpugida, Eremobatidae) along an altitudinal gradient. Bulletin of the British Arachnological Society, 9: 256-            262.

Punzo, F. 1998. The Biology of Camel-spiders (Arachnida, Solifugae).  Kluwer Academic Publishers, Boston.


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