PenderBlog From The Pender Islands Of Canada

September 26, 2011

Stop the invasion!

Filed under: Nature watch — Jocko @ 4:09 pm

Bullfrog Pair  
Photograph by S. Price; courtesy The Bullfrog Project
From the Pender Islands Farmers Institute:The American bullfrog is one of the 100 worst alien species in the world and is now found on Pender in increasing numbers.

Help stop the invasion!

The American bullfrog Rana (Lithobates) catesbeiana is a robust, brilliant green amphibian native to eastern North America.  However, its natural range does not extend across the prairies or west of the Rocky Mountains.

It is an unwelcome visitor!

Thriving populations of bullfrogs are now found all over the world because people have imported and released them.  This has resulted in unwanted, noisy, and ecologically damaging American bullfrog populations.

What’s the problem?

  • Adults are carnivorous and feed ravinously.
  • They eat anything they can swallow, including native birds, invertebrates, mammals, fish, reptiles, frogs (even other bullfrogs), newts and salamanders.
  • Bullfrogs’ prey includes endangered species like painted turtles and economically important species like coho salmon.
  • Bullfrogs decimate native species through direct predation and competition for food resources.
  • On Pender there are few, if any, natural predators.
  • Native ecosystems are at risk, including riparian zones.

What’s the solution?

  • Humane removal of bullfrogs without disturbing other species.
  • Complete eradication on Pender may take 2-4 years, as existing tadpoles mature at varying rates.

What does it look like?

  • No pair of raised lines (dorso-lateral ridges) on it’s back.
  • Huge tadpoles; up to 10 cm.

What does it sound like?

  • Juveniles make a “meep” sound when startled.
  • Adult males make a very loud, sonorous basso profundo mating call that sounds like the distant roar of a bull.

Life Cycle (lifespan about 5 years)


  • Tadpoles, juveniles and adults sit at the bottom of lakes or ponds in a cold-induced torpor.


  • As water warms up, tadpoles and frogs emerge, and can be seen along pond margins and surface, and hopping around on land.


  • Major growth (and eating) period.
  • They grow up to 8″ (20 cm) long, *plus legs!* and 1.5 lbs (750 g).
  • Each adult female deposits up to 20,000 eggs in a jelly-like mass.
  • Tadpoles hatch from eggs; may take 2-4 years to mature.
  • Tadpoles and frogs are not preferred by potential predators.

Late Summer – Fall

  • Juveniles migrate to nearby ponds, spreading the population.

Success stories

  • Bullfrog eradication program on Vancouver Island has collected over 15,000 bullfrogs, and examined the stomach contents of over 5,400.
  • Numbers can be driven down to zero in 4 years or less.

How to help

For more information, or to volunteer  or contribute to the Bullfrog Eradication Project, please contact:

Dianne Allison  250 629-3372  or  Margaret Alpen  250 539-0848

Please make any donations payable to:

Pender Islands Farmer’s Institute, PO Box 38, Pender Island, BC, V0N 2M0 (Attn Bullfrog Eradication Project)

More Information:


With thanks to Stan Orchard and

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