During drier periods frogs are usually restricted to the stream bed itself. Unlike most frogs, Ascaphus are not known to be vocal. Males may call while underwater but there is no evidence at present. Females retain viable sperm in the lower portion of the oviduct for several months, and fertilized eggs are laid during the summer after mating. Eggs hatch in about a month and aquatic larvae require 2 to 3 years to transform.
Metamorphosis normally occurs in the early fall.
A variety of amphibians, including Rhyacotriton variegatus, Dicamptodon ensatus, Ambystoma macrodactylum, Bufo boreas, Hyla regilla, Rana pretiosa and Rana boylei, all commonly coexist with Ascaphus. Whether or not competition for resources occurs between these species is unknown. Garter snakes have been known to take both tadpoles and adults, although in captivity they have been observed to reject adult Ascaphus after initially capturing them. Dicamptodon larvae and adult Rana boylei are known to eat tailed frog tadpoles, and trout have been observed to take both tadpoles and adults. Extensive logging activities may adversely affect existing tailed frog populations.