Tim Fitzharris / Little Pigeon River cascading among rocks and colorful Maple leaves, Great Smoky Mountains National Park, Tennessee

Jan Hamrsky / Large red damselfly nymph (Pyrrhosoma nymphula) with a sludge worm prey, Europe, October. Controlled conditions.

Jan Hamrsky / Sludge worm (Tubifex tubifex) hiding in the sediments, Europe, May, controlled conditions

Kim Taylor / Sludge worms (Tubifex sp) congregating at the bottom of a pond in mid-winter, Surrey, England

Jane Burton / Discus fish {Symphysodon discus} about to eat a {Tubifex sp} worm, captive, from tropical rainforest rivers in Brazil

Willem Kolvoort / Sludge worms (Tubifex rivilorum) These worms live in the sludge of nutrient rich waters and factory effluents. Aquarium, Holland

Willem Kolvoort / Sludge worms (Tubifex rivilorum) These worms live in the sludge of nutrient rich waters and factory effluents. Aquarium, Holland

Kim Taylor / Tubifex worm {Tubificidae}

Kim Taylor / Tubifex worm {Tubificidae}

Kim Taylor / Tubifex worm {Tubificidae}

Kim Taylor / Young Tubifex worms {Tubificidae sp.}. UK.

Will Watson / Tubifex worms (Tubifex tubifex) on the base of a muddy pond, Herefordshire, England, UK. July.