Two-toothed Goldenring
Cordulegaster bidentata
The Two-toothed Goldenring is a large, striking dragonfly with a bold black and yellow pattern and green eyes. It inhabits small, calcium-rich spring brooks and mountain streams in forested upland areas. The larvae spend three to five years developing while buried in the sediment of these specific, cool habitats.
Details
Identification
Two yellow diagonal stripes on the sides of the thorax; yellow abdominal rings interrupted in the middle; females have a long ovipositor.
Social behavior
Solitary; males patrol persistently along spring brooks and defend small territories against rivals.
Diet
Larvae feed on freshwater amphipods and other aquatic insect larvae; adults hunt flies, mosquitoes, and smaller dragonflies.
Hunting strategy
Larvae are ambush predators in the sediment; adults are active aerial hunters that catch prey in flight.
Spawning substrate
Fine sediment, sand, and detritus in shallow, slow-moving spring rivulets.
Overwintering
Overwintering occurs multiple times as larvae within the substrate of the water body bed.
Ecology
Ecological role
Important predator in fish-free spring waters; regulates populations of smaller invertebrates.
Natural predators
Birds (e.g., Grey Wagtail), larger dragonflies, spiders (for adults), predatory beetle larvae (for young larvae).
Competitor species
Golden-ringed Dragonfly (Cordulegaster boltonii) in lower elevations.
Ecosystem service
Biological control of mosquito populations; serves as an indicator for the condition of drinking water resources.
Threats
Destruction of springs through capping, lowering of groundwater levels, spruce afforestation, and climate change (drought).
Scientific profile
Profile
Distinguishing features
The most important feature for distinguishing it from Cordulegaster boltonii is the presence of two separate yellow spots on the frons (in boltonii, a continuous transverse band). The occipital triangle is black in bidentata (yellow in boltonii). Larvae possess a deeply serrated, spoon-shaped labial mask without lateral spines on the abdomen.