Opiliones

Easily distinguished from spiders (Araneae) by: fused body regions without constricted waist (pedicel); single pair of eyes (vs. three to four pairs in spiders); absence of silk glands and web-building behavior; absence of venom glands in chelicerae; tracheal respiration (vs. book lungs in most spiders); direct copulation with penis in males (vs. indirect sperm transfer via pedipalps in spiders). Distinguished from Solifugae (camel spiders) by smaller size, different eye arrangement, and lack of massive chelicerae. Distinguished from Pseudoscorpiones by absence of pincer-like pedipalps and lack of venom apparatus. The ocularium—a raised structure bearing the eyes—is a key diagnostic feature visible in lateral view. Some families (e.g., Cosmetidae) have distinctive spoon-shaped pedipalps.

Body divided into two tagmata: anterior cephalothorax (prosoma) and posterior 10-segmented abdomen (opisthosoma). Most distinctive feature is the broad, fused connection between cephalothorax and abdomen, creating a single oval body structure without the constricted waist seen in spiders. Body length typically under 7 mm, though some species reach 22 mm. Legs are often exceptionally long relative to body size, with leg spans sometimes exceeding 160 mm and reaching 340 mm in Southeast Asian species; however, some groups (particularly Laniatores) have short, robust legs. Second pair of legs is longest and functions as sensory appendages analogous to antennae. Single pair of camera-type eyes positioned medially on the cephalothorax (except Cyphophthalmi, which have lateral eyes or are eyeless; cave-adapted species frequently lack eyes entirely). Chelicerae are small grasping claws without venom glands. Pedipalps vary from slender to heavily modified. Some species possess a dorsal scutum formed from fused abdominal segments. Spiracles located between base of fourth leg pair and abdomen; additional spiracles may occur on leg tibiae in active species.

Inhabits diverse terrestrial environments including forests, grasslands, caves, and human-modified landscapes. Most abundant in moist, protected microhabitats: under rocks, logs, leaf litter, and bark. Cave-dwelling species (troglobites) occur in subterranean systems worldwide, with many showing reduced eyes and pigmentation. Some species occupy specialized habitats including termite nests. Vertical distribution ranges from ground level to forest canopy. Many species aggregate in sheltered sites near water sources. Specific habitat associations vary by suborder: Cyphophthalmi are small, soil-dwelling or cave-dwelling; Eupnoi and Dyspnoi include many long-legged forms of open habitats and forests; Laniatores are predominantly tropical forest floor dwellers with short legs.

Cosmopolitan distribution on all continents except Antarctica. Representatives of all four extant suborders occur on each inhabited continent. Highest diversity in tropical regions, particularly in the Neotropics and Southeast Asia. Canada hosts 36 native and 7 non-native species across 8 families. Western North America (British Columbia) better studied than central and eastern provinces. Some species show extremely restricted ranges (short-range endemics), particularly in mountainous regions of southern Oregon and cave systems. Four Brazilian cave-dwelling species are nationally endangered; several Argentine species are vulnerable due to habitat destruction.

Most species are nocturnal and active year-round in suitable climates, with activity influenced by moisture availability. Some temperate species show seasonal peaks: Trachyrhinus favosus in western North America is active only during fall. Reproductive timing varies; females may lay eggs shortly after mating or delay oviposition for several months. Egg development ranges from 20 days to six months depending on temperature. Most species complete life cycle within one year.

Omnivorous and opportunistic feeding habits documented, including: small insects, other arthropods, plant material, fungi, and decaying organic matter. Some species are active predators, others scavengers. Novel observations confirm predation on live vertebrates: at least four species of Neotropical Cranaidae harvestmen have been documented capturing and consuming adult frogs (Pristimantis, Dendropsophus, Atelopus), subduing prey several times their own body size using robust chelicerae and spined pedipalps. Some species use viscoelastic adhesive secretions from pedipalp hairs to trap springtails and other small prey. Certain groups specialize on snails (e.g., Nipponopsalis, Ischyropsalis) using enlarged chelicerae to crack shells.

Development includes egg stage and four to eight nymphal instars; most species have six instars. Sexual reproduction predominates, though parthenogenetic species occur. Males possess a penis for direct sperm transfer (unique among arachnids except some mites); females store aflagellate, immobile sperm at the ovipositor tip for fertilization during egg-laying. Some species exhibit parental care: males guard eggs from multiple partners against predation (including by conspecific females) and clean eggs regularly. Paternal care has evolved independently at least three times within Laniatores. Some species build nests for oviposition.

Second pair of legs used as sensory appendages to explore environment, compensating for eyes that cannot form images. Defensive behaviors include: thanatosis (feigning death, common in Dyspnoi and Laniatores); freezing (complete movement halt in Sclerosomatidae); bobbing (vigorous body bouncing to blur body form, observed in Eupnoi); autotomy (voluntary leg amputation when captured—legs do not regenerate and autotomized legs may twitch for minutes to an hour, distracting predators); fleeing; stridulation (sound production in Laniatores and Dyspnoi); chemical secretion from ozopores; and retaliation using spines and chelicerae. Gregarious behavior common: aggregations of 200+ individuals in Laniatores, exceeding 70,000 in some Eupnoi, likely serving anti-predator and microclimate-regulation functions. Post-copulatory behavior includes males shaking female sensory legs to encourage remating. Leg grooming after feeding by drawing legs through chelicerae.

Function as omnivores, detritivores, predators, and scavengers in terrestrial food webs. Documented as opportunistic mesopredators capable of consuming vertebrate prey, expanding their recognized trophic position beyond traditional views. Aggregations may influence local nutrient cycling and microhabitat conditions. Serve as prey for various vertebrates and invertebrates including mammals, amphibians, spiders, and scorpions. Chemical defenses and aposematic coloration may influence predator learning and community dynamics. Host to parasitic and phoretic mites (Erythraeidae, Trombidiidae, potentially Histiostomatidae). Poorly studied ecosystem role in many regions; non-native species may have undocumented ecological impacts.

Subject of persistent urban legend falsely claiming they are highly venomous but unable to bite humans—actually possess no venom glands and chelicerae are too small to pierce human skin. Scientifically understudied group with limited taxonomic expertise; Carl Friedrich Roewer described over 2,000 species in the early-to-mid 20th century. Recent establishment of Phalangium opilio as a model system for arachnid comparative genomics and evolutionary-developmental biology. Several cave-dwelling species are endangered due to habitat destruction and restricted ranges, with conservation concern in Brazil, Argentina, United States (Texas, California), and Spain (Canary Islands). Some species may serve as indicators of habitat quality and climate conditions due to moisture requirements.

• Araneae (spiders)Superficially similar long-legged forms; distinguished by constricted waist between body regions, multiple eye pairs, venom glands, silk production, and book lungs
• Pholcidae (cellar spiders)Also called 'daddy longlegs'; true spiders with distinct abdomen, eight eyes, and web-building behavior
• Tipuloidea (crane flies)Dipteran insects with extremely long legs; possess single pair of wings and completely different body plan
• Solifugae (camel spiders/sun spiders)Large, fast arachnids with massive chelicerae and different eye arrangement; lack fused body structure

Widespread false belief that harvestmen are highly venomous but cannot bite humans due to small mouthparts. In reality, Opiliones completely lack venom glands; their chelicerae are small grasping claws, not hollow fangs, and are typically incapable of breaking human skin. This myth is also erroneously applied to cellar spiders (Pholcidae) and crane flies (Tipulidae).

• arachnid
• harvestman
• daddy longlegs
• ancient lineage
• omnivore
• nocturnal
• gregarious
• cave-dwelling
• paternal care
• chemical defense
• autotomy
• model organism
• conservation concern
• venomless
• tracheal respiration
• direct copulation
• short-range endemic
• troglobite
• aposematic
• crypsis
• mimicry
• thanatosis
• viscoelastic adhesive
• anurophagy
• vertebrate predator

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Opiliones | Blog
• Harvestmen Use Glue to Capture Prey
• Answer to Super Crop Challenge #1 | Beetles In The Bush
• Cosmetid harvestman with parasitic/phoretic mites in Argentina | Beetles In The Bush
• Phreaky Phalangid | Beetles In The Bush
• Opiliones of Canada
• Distribution of harvestmen of the genus Paranemastoma Redikorzev, 1936 (Opiliones: Nemastomatidae) in Poland / Rozmieszczenie kosarzy z rodzaju Paranemastoma Redikorzev, 1936 (Opiliones: Nemastomatidae) w Polsce
• Harvestmen (Arachnida: Opiliones) as Overlooked Predators of Anurans in the Neotropics.
• Influence of light levels and predator characteristics on the functional response of the European harvestman (Opiliones: Phalangiidae).