• Whip Spiders (Amblypygi)

    Also known as tailless whip scorpions, these animals have extremely long antenna-like front legs and raptorial pedipalps. Adult body size is typically 20-60 mm. They are found in tropical and arid regions, often in caves. There are approximately 175 described species. 

  • Spiders (Araneae)

    Spiders have abdominal silk organs, male pedipalps modified into sperm transfer organs, and venom delivered through the chelicerae (secondarily lost in some spiders). Adult body size ranges from less than 1 to 100 mm. They are diverse and abundant worldwide with more than 45,000 described species. 

  • Harvestmen (Opiliones)

    Also known as daddy long legs among other names, they are distinct from spiders in lacking venom and silk, and males transfer sperm through a penis. Adult body size ranges from less than 1 to 25 mm. More than 6,500 species are described worldwide. 

  • Micro whipscorpions (Palpigradi)

    These small (1-3 mm) delicate arachnids are found in tropical leaf litter and caves. They have a thin, pale, segmented integument, and a segmented abdomen that terminates in a whip-like flagellum. Fewer than 100 species have been described. 

  • Pseudoscorpions (Pseudoscorpiones)

    Pseudoscorpions look like small (2-12 mm) scorpions without the tail. Their pedipalps can have venom glands and the chelicerae have silk glands. There are more than 3,600 species described worldwide, typically found in leaf litter, caves, and under tree bark. 

  • Hooded tickspiders (Ricinulei)

    These small (3-10 mm) cave and soil-dwelling arachnids can be found in the African and New World tropics. The male third leg is modified as a sperm transfer organ. Fewer than 80 species have been described. 

  • Short-tailed Whipscorpion (Schizomida)
    These small (3-13 mm) tropical soil and cave-dwelling arachnids are moderately fast runners. Reproduction is via a spermatophore attached to the substrate. More than 300 species have been described. 

  • Scorpions (Scorpiones)

    Scorpions are easily recognized by their venom-tipped tail and large pinching pedipalps. In addition to the arid ecosystems, scorpions occur in a wide range of habitats. Adult body size ranges from 1 to 20 cm. Nearly 2,000 species have been described. 

  • Windscorpions (Solifugae)

    Also known as camel spiders, sun spiders, and solifuges, among other names, these nocturnal, fast-running hunters are notable for their large chelicerae. They occur mostly in arid habitats. They range in size from 20-70 mm. There are more than 1,100 described species. 

  • Whip Scorpions (Thelyphonida)

    These are robust tropical predators with raptorial pedipalps and a long whip-like tail. They possess anal glands from which they spray defensive chemicals including acetic acid. Because of this, they are also known as vinegaroons. They range in size from 25-85 mm. There are about 100 species described. 

  • Mites and Ticks (Acari)

    With more than 50,000 described species, this is the most diverse and abundant arachnid order. Large numbers of species remain undescribed. They are ubiquitous in terrestrial habitats and include vectors of animal and plant diseases, and parasitic forms. The monophyly of mites is far from certain, with 2-3 distinct lineages. They range in size from less than 0.1 to 16 mm. 

International Society of Arachnology

The International Society of Arachnology (ISA) is the premier international scientific society devoted to arachnology. ISA focuses on all arachnid orders. Currently ISA has about 500 members from 70 countries. ISA's goals are to promote the study of Arachnology and communication of arachnological information among researchers via meetings and publications.

The ISA organizes the International Congress of Arachnology every three years. Recent congresses have been held in Taiwan, Poland, Brazil, Belgium, and South Africa. The Congress features symposia of current interest and contributed papers. 

The society maintains a database of members including contact information and professional interests to facilitate communication among arachnologists.

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  • Facts about Arachnids

    Information about the different Arachnid orders including links and recent publications.

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    22nd International Congress of Arachnology

    Upcoming meeting of the ISA - March 2023 in Montevideo (Uruguay).

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    World Spider Catalog

    First fully searchable online database covering spider taxonomy.

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  • Institutions

    Overview of institutions housing Arachnid collections.

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    List of scientific journals devoted to Arachnology.

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    Overview of international and national societies devoted to Arachnology.

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