Running Crab Spiders

Philodromidae

Classification

Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae
Infraorder: Araneomorphae
Family: Philodromidae

Pronunciation

How to pronounce Philodromidae: /fɪloʊˈdroʊmɪˌdeɪ/

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Summary

Philodromidae, known as running crab spiders or philodromid crab spiders, comprises a diverse family of araneomorph spiders characterized by their sideways-oriented legs, effective ambush predation strategy, and wide distribution. They inhabit various plant structures and play a role in controlling insect populations.

Physical Characteristics

Philodromids have a crab-like shape due to the first two pairs of legs being oriented sideways (laterigrade). They usually exhibit cream to light brown coloration with faint longitudinal stripes. The second pair of legs may be significantly longer than the first pair, particularly evident in some Ebo species. They have eyes arranged in two curved rows, with the posterior row wider than the anterior row.

Identification Tips

Philodromids can be distinguished from Thomisid crab spiders by having legs that are generally similar in size, while Thomisids have longer, more slender third and fourth legs. Additionally, the second pair of legs in Philodromids is often significantly longer than the first, which is a key identification feature.

Habitat

Philodromidae are usually found on the stems and leaves of plants. Some species are associated with deciduous trees, others with conifers, and a few inhabit desert environments.

Distribution

Widespread, particularly in North America, with over 500 species identified worldwide.

Diet

Philodromids are active predators that do not build webs to catch prey, hunting by ambush instead.

Ecosystem Role

Philodromids serve as predators in their ecosystems, helping to control insect populations.

Evolution

Originally described as a subfamily (Philodrominae) within Thomisidae by Tord Tamerlan Teodor Thorell in 1870, Philodromidae is now recognized as a distinct family with over 500 species across thirty genera.

Similar Taxa

Misconceptions

Philodromids are often confused with true crab spiders (Thomisidae), but they are not as closely related as initially thought.