Duchess of Dirt: Species bioinvasion – from foxglove to bullfrogs

Purple foxglove (Digitalis purpurea) was used medicinally in its native European regions. It likely arrived in North America in a shipment with other herbs imported from Europe. Photo via Wikimedia Commons

Leslie Cox

Special to The Record

I first wrote about species bioinvasion in a 2014 column, but based on a few finds in our garden this year, the subject bears mentioning again.

As words go, “bioinvasion” is a relatively new term. It is used to describe an invasion of any non-native species. And thanks to the global reach of human activity through all forms of transport – land, sea and air – there has been an alarming increase of exotic species introduced to foreign soils over the last couple of centuries.

Plant hunters have been hugely instrumental in eradicating botanical boundaries. They have been traipsing all over the world in search of exciting horticultural beauties and culinary delights with which to tempt home gardeners.

Purple loosestrife, Lythrum salicaria, was once native to Europe where it was valued as a medicinal herb to treat wounds, ulcers, diarrhea and dysentery. This plant found its way to North America in the late-1800s, included in a shipment of assorted herbs. (My research revealed additional benefits of purple loosestrife in treating upper respiratory infections, Crohn’s disease, irritable bowel syndrome, as well as aiding in lowering blood sugar levels…to name a few.)

Digitalis purpurea, or purple foxglove as it is known, is another plant species which was used medicinally in its native European regions. And as a medicinal herb, it is fairly safe to assume foxglove found its way to North America in a similar manner as purple loosestrife – included in a shipment with other herbs imported from Europe.

Then there is the Norway maple, Acer platanoides, native to central Europe and east into western Asia. It was originally introduced to North America as an ornamental replacement for the elm trees which were succumbing to the devastating Dutch elm disease. Now the Norway maple is considered an invasive pest in its own right and is banned in many parts of North America. (It is listed on the BC Invasive list as a “minor upland invasive.”) We are guilty of having this one in our garden.

The list of invasive plants goes on… but what about invasive animals?

John just spotted another American bullfrog in our garden. We also saw two others in our pond earlier this spring but could not catch them, unfortunately.

It is a royal battle with this cold-blooded amphibian. Their appetite is voracious and their breeding prowess is phenomenal. On their menu is anything they can fit in their mouth. This includes: insects, fish, snakes, other frogs (even smaller bullfrogs), small mammals, and birds – even ducklings. Of great concern is their appetite for our native frog species, such as the red-legged which is on the BC Blue List. (The Blue List contains species whose population decline is “of concern.”)

As for procreation abilities, female American bullfrogs lay roughly 25,000 eggs per year compared to the 6,000 eggs laid by the red-legged frog. Upsetting. And to think all of this started with a culinary desire for frog legs.

Early in the 20th century, someone imported a few bullfrogs to B.C. from their native eastern North America with a plan of raising them for the restaurant trade. Suffice to say, the delicacy did not take off and they escaped into the wild where they have become a real problem. (It is now illegal to release American bullfrogs into the wild. If you have them in your garden, they must be dispatched with… if you get my drift.)

Oh, and I forgot to mention… these bullfrogs have few predators in our region. They have a nasty taste which deters all the usual prey species who like to dine on frogs. As you can see, that leaves the onus of eradication up to us. Time to acquire a taste for frogs’ legs, me thinks.

Leslie Cox co-owns Growing Concern Cottage Garden in Black Creek. Her website is at www.duchessofdirt.ca and her column appears every second Thursday in The Record.

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