Expensive Frogs

The British Columbia taxpayers have paid about $250,000 to fight the invasion of bullfrogs (Rana catesbeiana) in the Osoyoos region in southern B.C. Estimates for control programs for the entire province run into the tens of millions.

Why get rid of bullfrogs? They are not native to B.C. and they are eating the young of all the native frogs, threatening some with extinction. In addition, bullfrogs carry a chytrid skin fungus that is deadly to many other frogs. Many frogs are declining globally.

How did bullfrogs get into B.C.? Non-thinking speculators in frog leg farming brought some in. Others were brought in by gardeners just for the aesthetics of their lily ponds.

Green frogs (Rana clamitans) also have been introduced but are less menacing. We have many green frogs in the Land Between  and some bullfrogs. Why don’t we have the problems seen in B.C.? Our other frogs have lived with bullfrogs over evolutionary time and have developed adaptations to prevent population decline due to bullfrog predation on their young. Possibly we also have predators that hold back the bullfrog population. Otters eat both bullfrogs and green frogs that the otters catch in winter on the muddy bottom and bring up to eat on the edge of the ice. The amphibian species native to B.C. have not had the benefit of adapting over a long time to the bullfrogs.

These costly frogs are just one example of many costly invasions caused by humans moving species into ecological systems not adapted to the imported species. Consider purple loosestrife, arrived here from gardens in New England. We got Zebra mussels compliments of sea-going transportation with follow-up help from local boaters. Carp are not native to Ontario and we now are threatened by additional exotic carp species whose spread is supported by our engineering projects. European Phragmites or giant reed is expanding from an initial seeding by following the ditches along our highways. Phragmites and purple loosestrife take their choices from the habitat opportunities presented by road maintenance contracts that are insensitive to environmental effects.

Take home message? Stop moving exotics around. Some of them can become costly invasives that will threaten our native species. Learn to identify and eliminate invasives before they spread.

Written by: Gray Merriam