Body regions
Cephalothorax (prosoma): fused head and thorax bearing the eyes, chelicerae, pedipalps, and eight legs.
Abdomen (opisthosoma): bears the spinnerets, book lungs, and reproductive structures.
Features used in identification
Eye pattern: number, size, and arrangement of eyes. Diagnostic at the family level (recluses have six eyes in three pairs; jumping spiders have a large anterior median pair).
Leg span vs. body length: leg span is measured tip to tip on opposite legs and is often more useful for non-specialists than body length.
References
- [1]World Spider Catalog - Natural History Museum Bern. Accessed June 2026.
Related in Reference
- Spider taxonomy: families covered on this siteA working list of the spider families most relevant to human-built environments in North America, with diagnostic notes..
- How body and leg measurements are reportedReported sizes vary widely across sources.
- Common US spider families - quick referenceDiagnostic summary of the ten spider families most often encountered in and around US homes, with the key trait that distinguishes each at first sight..
- Spider bite versus other arthropod bitesMost presumed spider bites are caused by other arthropods or by infection.
- Identification trait glossaryPlain-language definitions of the terms used on species pages: carapace, sternum, epigynum, scopula, calamistrum, cribellum, trichobothria, and more..