Spiders are an ancient, diverse group of arthropods that have adapted to nearly every terrestrial habitat on Earth. They are the largest order of arachnids, characterized by eight legs and the ability to produce silk. Their ecological role as predators is globally significant, and the vast number of species, many of which remain undiscovered, is far greater than most people realize.
The Latest Global Species Tally
The current, accepted approximate count of described spider species is approximately 53,600, cataloged across 139 recognized families. This figure is tracked and maintained by the authoritative World Spider Catalog (WSC), a database based at the Natural History Museum of Bern. Spiders rank as the seventh-most species-rich order among all organisms, demonstrating immense biological success.
This number represents only the species that have been formally described by scientists. Arachnologists estimate that the actual total number of spider species may be closer to 100,000, suggesting that roughly half of the world’s spiders have yet to be documented. The rate of discovery is accelerating; it took 265 years from the first scientific description in 1757 to reach 50,000 species, but experts believe it could take less than 100 more years to discover the next 50,000.
The Process of Discovery and Classification
To formally classify a new spider, a scientist must first collect a specimen, often from an undersampled region like tropical rainforests or remote caves. The specimen then undergoes detailed morphological analysis, where physical features, especially the unique structure of the mating organs, are examined under a microscope.
Modern classification also relies heavily on molecular analysis, using genomic data like DNA and RNA to confirm evolutionary relationships and species boundaries. Once the species is determined to be distinct from all others, the taxonomist publishes a formal description in a peer-reviewed scientific journal, adhering to established rules of nomenclature. This publication officially validates the new species, which is then added to the World Spider Catalog.
The continuous influx of new discoveries is largely due to intensified fieldwork in previously unexplored regions. The availability of centralized online databases has also streamlined the process of tracking these changes, allowing researchers to rapidly compare new findings against existing knowledge.
Understanding Spider Diversity Through Taxonomy
The substantial number of described species is organized into major taxonomic groups reflecting the vast array of spider forms and behaviors. The largest group, comprising about 90% of all species, is the infraorder Araneomorphae, often called “modern” spiders. The other major group is the Mygalomorphae, which includes “ancient” spiders like tarantulas and trapdoor spiders.
The family Theraphosidae, or tarantulas, belongs to the Mygalomorphae. They are characterized by a robust, often hairy build and large fangs that move parallel to each other, stabbing downward. These spiders are ambush predators, living in burrows or trees, and are notable for their long lifespans, with some females living for over two decades.
The largest spider family within the modern group is Salticidae, the jumping spiders, with over 6,000 described species. These spiders are active, diurnal hunters that do not build webs for prey capture. Instead, they rely on some of the best vision in the arthropod world to stalk and pounce on prey. Their signature is an arrangement of four pairs of eyes, including a set of large, forward-facing eyes used for acute stereoscopic vision.
Another prominent family is Araneidae, the orb weavers, famous for constructing the stereotypical, circular, wheel-shaped webs found in gardens and fields. These spiders build a non-sticky silk framework before adding a spiral of sticky capture silk, relying on web vibrations to detect captured insects.
The Linyphiidae, commonly known as sheet weavers or dwarf spiders, represent the second-largest family, with nearly 5,000 known members. These spiders are generally small, often measuring only a few millimeters, and construct fine, horizontal sheet-like webs close to the ground or in low vegetation. Many species are known for their ability to disperse vast distances using a behavior called ballooning, where they release a silk thread and are carried aloft by the wind.