Uropygi

Distinguished from true scorpions (Scorpiones) by the absence of a stinger and venom glands, and by the presence of a slender whip-like flagellum rather than a segmented tail with terminal stinger. Distinguished from whip spiders (Amblypygi) by the presence of the tail-like flagellum (Amblypygi are "tailless"). Distinguished from Schizomida (short-tailed whipscorpions) by flagellum length and body proportions; Schizomida have a much shorter flagellum and smaller body size. The vinegar-like defensive spray is diagnostic when observed.

Body length ranges from 25–85 mm, with most species under 30 mm; the largest species, Mastigoproctus, reaches 85 mm. The opisthosoma consists of 12 segments: the first forms a pedicel, the next eight have dorsal tergites, and the last three are fused into a pygidium ending in a flagellum of 30–40 units. Large scorpion-like pedipalps bear an additional prominent spine on each palpal tibia. One pair of median eyes is positioned at the front of the cephalothorax, with up to five pairs of lateral eyes on each side. The first two leg pairs are elongated and function as antenna-like sensory organs, leaving six legs for locomotion.

Primarily inhabit tropical and subtropical regions, favoring humid, dark microhabitats under logs, rotting wood, rocks, and natural debris. Most species dig burrows using their pedipalps. Some species, such as Mastigoproctus giganteus, occupy more arid environments including hard adobe soils in Arizona and New Mexico, where they utilize shelter sites in soil cracks and rodent burrows.

Found in tropical and subtropical areas worldwide, excluding Europe and Australia. In the Americas, ranging from the southern United States through Central and South America. In Asia, distributed from India through Southeast Asia to Japan. Present in the Caribbean. Only a single African species is known: Etienneus africanus, endemic to Senegal, The Gambia, and Guinea-Bissau, considered a probable Gondwana relict.

Carnivorous, feeding primarily on insects, millipedes, scorpions, and terrestrial isopods. Occasionally consume worms and slugs. The giant whip scorpion Mastigoproctus giganteus has been observed preying on small vertebrates. Prey is captured and crushed using specialized teeth on the inner surfaces of trochanters on the front appendages.

Postembryonic development consists of four nymphal stages, with molting occurring approximately once per year. Development to maturity requires approximately four years. The adult stage does not molt again. Females extrude up to 40 eggs within a membranous broodsac attached to the genital operculum and fifth opisthosomal segment. During the several-month incubation period, the female fasts and arches her opisthosoma upward to prevent broodsac contact with the substrate. Eggs develop into postembryos with visible appendages, then hatch into white young that climb onto the mother's back and attach with specialized suckers. After the first molt, when they resemble miniature adults with bright red palps, young disperse from the maternal burrow. Females may survive up to two additional years after offspring departure. Total adult lifespan reaches up to four years.

Strictly nocturnal, avoiding light. Construct and occupy burrows, transporting prey to these shelters. When threatened, discharge a defensive spray containing acetic acid and caprylic acid from glands near the rear of the abdomen, producing a strong vinegar-like odor. Courtship involves complex tactile interactions: males grasp the female's antenniform legs with their chelicerae, followed by a "mating parade" in which the male deposits a spermatophore on the substrate and maneuvers the female over it. Males of some genera use their pedipalps to push spermatophore components into the female gonopore. Multiple sequential matings have been documented in some species.

Predators of soil and litter arthropods, potentially influencing population dynamics of insects, millipedes, and other invertebrates in their habitats. Their burrowing activity may contribute to soil aeration and nutrient mixing in tropical and subtropical ecosystems.

Occasionally kept in the pet trade, where they are valued for their distinctive appearance and relatively manageable care requirements. Defensive spray, while unpleasant, is not medically significant. Misidentification in social media and popular culture has led to exaggerated fear responses; they are harmless to humans. Educational displays in museums and universities utilize live specimens to demonstrate arachnid diversity and defensive adaptations.

• Amblypygi (whip spiders/tailless whip scorpions)Similar large pedipalps and elongated first leg pairs used as sensory appendages, but lack the posterior flagellum entirely; more slender body and typically cave or crevice-dwelling.
• Schizomida (short-tailed whipscorpions)Also possess a flagellum, but it is much shorter and less conspicuous; body typically smaller and more compact; often treated as a separate order or as Uropygi sensu lato depending on classification system.
• Scorpiones (true scorpions)Similar overall body plan with large pedipalps and segmented abdomen, but possess a venomous stinger on a segmented tail rather than a non-venomous whip-like flagellum; have venom glands and different defensive strategy.

Despite common names suggesting otherwise, Uropygi are not scorpions and possess no venom or stinger. The "whip" is a sensory and defensive structure, not a weapon. They are frequently misidentified as spiders or as dangerous animals in viral social media content; they are harmless to humans and their defensive spray, while malodorous, causes no lasting harm.

• arachnid
• predator
• nocturnal
• burrowing
• chemical defense
• parental care
• tropical
• subtropical

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• An Introduction to Dragonflies and Spiders | Bug Squad
• Bohart Open House: Dispelling Myths About Spiders | Bug Squad
• Bug Eric: When "Arachtober" Attacks!
• Bug Eric: Another Viral Internet "Monster"
• Paarungsverhalten und Spermatophorenmorphologie bei Geißelskorpionen:Thelyphonellus amazonicus Butler undTypopeltis crucifer Pocock (Arachnida, Uropygi) Mating behaviour and spermatophore morphology in whip scorpions:Thelyphonellus amazonicus butler andTypopeltis crucifer pocock (Arachnida, uropygi)
• MATING AND MATERIAL BEHAVIOUR IN TELYPHONUS CAUDATUS L. (PEDIPALPI, HOLOPELTIDIA, UROPYGI)
• Mating behavior and spermatophore morphology of the whip scorpion Typopeltis dalyi Pocock, 1900 (Uropygi, Thelyphonida)
• Courtship Behaviour and Sperm Transfer in the Giant Whip Scorpion, Mastigoproctus Giganteus (Lucas) (Uropygi, Thelyphonidae)
• TYPES OF SHELTER SITES USED BY THE GIANT WHIPSCORPION MASTIGOPROCTUS GIGANTEUS (ARACHNIDA, UROPYGI) IN A HABITAT CHARACTERIZED BY HARD ADOBE SOILS
• Notes on the life history and reproductive biology of the Giant whip scorpion, Mastigoproctus giganteus (Uropygi, Thelyphonidae) from Florida