If you’ve visited this summer you may have noticed some very large frogs in the Reflecting Pool near the gift shop. These are American Bullfrogs (Lithobates catesbeianus). They are native to Eastern North America, and they are an introduced invasive species.
Bullfrogs invaded Vancouver Island and the rest of British Columbia after being imported here for frog leg farms. Preferring to keep their legs to themselves, some of the frogs escaped, and have now established themselves on Vancouver Island from Victoria to Campbell River as well as out to Port Alberni. Unfortunately, this now includes our main water feature here at Milner Gardens & Woodland.
American Bullfrogs are considered to be a serious threat to native wildlife. They are predators with large appetites who have been known to eat other frogs and salamanders, small rodents, and even small birds. In other words, they are not just competing with native wildlife for food, they are using native wildlife AS food.
Last summer, a mass of bullfrog eggs hatched in our Reflecting Pool. We responded by removing as many tadpoles as we could using a dipnet. More than 500 tadpoles were removed and humanely euthanized before we lost count. We also cut the vegetation back significantly to give them fewer places to hide.
This spring, inspired by a project from the Tsolum River Restoration Society, who are working on their own bullfrog eradication project in the Comox Valley, we attempted to trap the remaining tadpoles. Unfortunately, our trapping project had minimal success, partly because the tadpoles were beginning to transform into frogs by the time we had the trap setup figured out.
Fortunately, we did have success by monitoring the Reflecting Pool several times a week for eggs and catching frogs with a dipnet when we were able.
Since the beginning of July, we have removed 32 young bullfrogs and one very large adult bullfrog from the Reflecting Pool. The frogs were humanely euthanized and delivered to an instructor at Vancouver Island University’s main campus, where they will be used in coursework with students. Significantly, we also removed a giant egg mass and have not seen any more eggs since.
While controlling the bullfrogs will be an ongoing project, we are considering this summer a success. We’ve reduced our bullfrog numbers, successfully prevented the bullfrogs from breeding in our Reflecting Pool, and VIU students will benefit from our bullfrog removal efforts. With perseverance, we might just beat these aliens.
If you’d like more information about American Bullfrogs, start here.