Reed sac spider
Clubiona phragmitis
The reed sac spider is a medium-sized spider that typically inhabits the stems of common reed (Phragmites australis) and other riparian vegetation. It does not build capture webs but constructs silken retreats for resting during the day and for reproduction. Its coloration is usually an inconspicuous yellowish-brown to reddish, providing excellent camouflage in dried vegetation. It is widely distributed across the Palearctic and is a characteristic inhabitant of fens and silting zones.
Details
Identification
Prosoma reddish-brown, opisthosoma yellowish-grey to brown without distinct markings, legs uniformly light brown.
Social behavior
Solitary; exhibits complex courtship behavior at the silken retreats during the mating season.
Diet
Opportunistic predator of small insects such as midges, flies, aphids, and leafhoppers.
Hunting strategy
Active nocturnal hunter; prey is overpowered by direct lunging on the substrate without the use of a web.
Spawning substrate
Silken brood retreats, often constructed in folded reed leaves or remains of umbels.
Overwintering
Overwinters as subadult or adult in sturdy silk sacs within hollow plant stems or under loose bark.
Ecology
Ecological role
Important predator for regulating insect populations in wetland biotopes.
Natural predators
Insectivorous birds (e.g., reed warblers), spider wasps (Pompilidae), and predatory beetles.
Competitor species
Other sac spiders like Clubiona stagnatilis as well as various running spiders.
Ecosystem service
Biological pest control in wetlands adjacent to agricultural areas.
Threats
Habitat loss due to drainage of fens, shoreline stabilization, and large-scale burning of reed beds.
Scientific profile
Profile
Distinguishing features
Clubiona phragmitis exhibits the typical habitus of the genus with an elongated body and robust chelicerae. The anterior spinnerets are cylindrical and closely set. Reliable species identification requires examination of the genital structures (epigyne in females, palp in males). Its strong association with reed beds is also characteristic.
Habitat
Strongly tied to wetlands; particularly in extensive reed beds (Phragmites australis), sedge marshes, fens, and along the shores of standing or flowing waters.
Role in food web
Important predator in the reed belt ecosystem; regulates insect populations and serves as food for specialized birds (e.g., reed warblers) and parasitic wasps.
Protection & threats
Main threats
Destruction of wetlands, drainage measures, intensive reed harvesting, and the loss of natural riparian buffer zones.
Population trend
Widespread in Germany and Central Europe and common in suitable habitats; the population is currently considered stable.