Uloboridae

Thorell, 1869

hackled orb weavers, cribellate orb weavers

Genus Guides

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Uloboridae is a of spiders distinguished by their lack of venom glands, a secondarily evolved trait unique among arachnids. Instead of venom, they subdue prey through extensive silk wrapping and compression, followed by external digestion using regurgitated . Members of this family are known as cribellate orb weavers, producing specialized silk from an additional spinning organ called the cribellum, which is combed into tangled, non-sticky capture threads. The family includes both traditional orb web builders and with reduced web structures, such as the triangle spiders of Hyptiotes.

Uloborus by (c) Sagnik Dutta Roy, some rights reserved (CC BY), uploaded by Sagnik Dutta Roy. Used under a CC-BY license.Hyptiotes gertschi by no rights reserved, uploaded by Ellyne Geurts. Used under a CC0 license.Hyptiotes puebla by (c) jcowles, some rights reserved (CC BY), uploaded by jcowles. Used under a CC-BY license.

Pronunciation

How to pronounce Uloboridae: /ˌjuːloʊˈbɒrɪdiː/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Uloboridae can be distinguished from other orb-weaving by the presence of a cribellum and calamistrum, combined with the absence of venom glands. The humped and dull coloration separate them from more colorful Araneidae. Triangle spiders (Hyptiotes) build distinctive reduced webs that are triangular sectors of orb webs rather than complete circles. Featherlegged orb-weavers (Uloborus) display characteristic tufts on the front legs. Unlike ecribellate orb weavers that use adhesive silk, uloborid webs appear fuzzy or woolly due to the tangled cribellate threads.

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Appearance

Medium to large spiders with three claws and no venom glands. Body typically dull in coloration with effective camouflage. The opisthosoma () is characteristically humped, more prominently so than the . Most possess eight with rear eyes that tend to curve; however, the Miagrammopes has only four eyes. Many species display a tuft of hairs midway down each front leg, giving rise to the 'featherlegged orb-weavers.' Cribellate silk appears fuzzy or hackled rather than .

Habitat

Diverse including woodlands, deserts, suburban areas, and riparian zones. Some , such as Uloborus diversus in Arizona, construct webs in exposed desert locations near pack rat nests or in residential areas. Triangle spiders (Hyptiotes) build webs at waist height in weeds, on bridges, and on twigs of trees and shrubs. Many species occupy manmade structures including bridge railings, culvert openings, and building exteriors. The shows adaptability to both natural and anthropogenic environments.

Distribution

Almost worldwide distribution. In North America, found across the entire United States and southern Canada. In Europe, only two are known from Northern Europe: Uloborus walckenaerius and Hyptiotes paradoxus. Present in South America (documented in Minas Gerais, Brazil). The oldest known fossil is Talbragaraneus from the Late Jurassic (Tithonian) Talbragar Fossil Bed of Australia.

Diet

Insect prey captured in orb webs or reduced web structures. Prey is subdued without venom through extensive silk wrapping that compresses the body and can break appendages, followed by external digestion with regurgitated . The liquified prey is then ingested without the mouthparts ever touching the intact prey body.

Host Associations

  • parasitoid wasps - Attack sacs (), documented in Miagrammopes unipus in Brazil
  • dipterans - /Attack sacs
  • mantispids - Attack sacs
  • pack rats - associationUloborus diversus builds webs near pack rat nests in Arizona desert

Life Cycle

Females construct small, flattened, papery sacs, usually positioned near the periphery of the web; multiple sacs may be arranged in a row. Hatchlings emerge without cribellum and calamistrum, building webs with additional and retained auxiliary spiral at the hub. After the second , spiderlings develop these structures and construct typical cribellate webs. In some , colonies may be nymph-dominated or -dominated, with larger colonies showing higher male presence.

Behavior

Prey capture involves extensive wrapping in silk rather than venomous strike. Some , notably Hyptiotes, use a unique mechanism where the spider maintains tension on an anchor thread and releases it when prey strikes, causing the web to rebound and further entangle the victim. Philoponella congregabilis forms communal colonies ranging from a few individuals to several hundred, constructing large, messy shared webs; these colonies are female-dominated with males primarily found in larger colonies. Web construction varies: some build complete orbs, others build reduced triangular sectors, and some construct only single-line webs.

Ecological Role

Predatory spiders controlling insect . sacs serve as resources for specialized and including , dipterans, and mantispids. Maternal care provides a model system for studying in arthropods. In desert , Uloborus diversus demonstrates how web-building spiders modify behavior in response to wind exposure, with implications for understanding trade-offs between foraging and web damage.

Human Relevance

Generally harmless to humans due to lack of venom glands. Occasionally encountered indoors or on manmade structures. Some , such as the Bridge Orbweaver (Larinioides sericatus), are common in urban settings near water. The unique of this makes it of interest for arachnological research and public education about spider diversity.

Similar Taxa

  • AraneidaeBoth include orb web builders, but Araneidae possess venom glands and produce adhesive, ecribellate silk rather than cribellate silk; Araneidae typically lack the pronounced abdominal hump and cribellum/calamistrum structures of Uloboridae
  • TetragnathidaeLong-jawed orb weavers also build orb webs but possess venom glands, have elongated and body form, and use adhesive silk rather than cribellate capture threads

Misconceptions

A common misconception, even in some reference materials, is that all spiders are venomous. Uloboridae definitively lack venom glands, representing a rare exception among spiders. Another misconception is that orb webs with visible spiral patterns must be built by Araneidae; the cribellate silk of Uloboridae produces similar overall architecture but with functionally different capture mechanisms.

More Details

Web reduction and eye evolution

Studies of visual field reveal that uloborids with reduced webs show corresponding reductions in number and modifications to maintain visual surveillance. Hyptiotes cavatus retains six functional eyes despite losing lateral eye , while Miagrammopes animotus has lost all four anterior eyes but retains and surveillance through compensatory changes in the remaining eyes' visual angles.

Silk production

The cribellum is a plate-like spinning organ that produces extremely fine silk fibrils. The calamistrum, a row of specialized bristles on the of each hind leg, combs these fibrils into a woolly, tangled mass that effectively snags prey without adhesive. This represents a convergent solution to prey capture that evolved independently from the sticky silk of ecribellate orb weavers.

Prey subjugation without venom

The mechanism of prey killing involves severe compression through silk wrapping, which can break appendages and asphyxiate the prey, potentially aided by silk shrinkage as it dries. Digestive are then regurgitated onto the wrapped prey, and the liquified contents are ingested. Robust hairs on the spider are thought to protect it from its own digestive fluids.

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