Frog of the Week

Coastal Tailed Frog (Ascaphus truei)

Coatal Tailed Frog
Coastal Tailed Frog – photo by Ken-ichi Ueda


Common Name: Coastal Tailed Frog, Pacific Tailed Frog, and Western Tailed Frog
Scientific Name: Ascaphus truei
Family: Ascaphidae – Tailed Frog family
Location: United States and Canada
US Locations: California, Oregon, and Washington
Size: 1-2 inches (2.5-5.1 mm)

The Coastal Tailed Frog is named for the tail-like extension on their cloaca of the males that is  used during breeding. Most frogs use external fertilization where the female lays the eggs and the males release their sperm on them. For Tailed Frogs, they use to tails to inseminate the female frogs internally, something that is rare for frogs. Breeding season starts in May and extends all the way to September.  Males do not call for females. They lay a relatively low number of eggs, under 100 in strings under rocks in streams. Tadpoles can take up to four years to fully undergo metamorphism. These young frogs can reach sexual maturity in at least 5 years but can take more.

They are primarily aquatic and live in cold, fast moving streams. They have evolved several adaptations for living in this environment. Their unusual reproduction method helps the frogs fertilize their eggs so that they don’t flow down stream. Their lungs are smaller in size to help decrease buoyancy and most respiration happens through the skin. The fingertips of the frogs are hardened to help them climb around the bottom of the fast moving streams.

Coastal Tailed Frogs have a relatively large life for a frog, spanning 15-20 years. They are also  part of one of the most ancient frog groups, the family Ascaphidae. There are only two species of frogs in the family, the Coastal Tailed Frog and the Rocky Mountain Tailed Frog (Ascaphus montanus). They share common traits with the first frogs to evolve, such as not vocalizing and nine presacral vertebrae. The family is only found in the western coast of North America.

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