American Bullfrog vs. The Western Toad

features-iconBy contributor James Mackinnon. Read more the Museum News series.

In the most recent issue of The Navigator (Vol. 46 No. 13, March 25 – April 7), this column featured Vancouver Island Amphibians. Unfortunately, a certain number of errors regarding the native Western Toad and the introduced American Bullfrog made it through the editing process and into print. On the surface, such an obvious and ironic mix-up seems a little comical, but closer consideration reveals the potential, and very detrimental, repercussions that this flub could have on the struggling Western Toad.

Over the past number of years, much time and effort has been dedicated to the understanding and conservation of the Western Toad and its corresponding habitat. Great minds have spent countless hours studying these toads and promoting their importance on Vancouver Island. The errors that were printed here had the potential to undo much of this amazing work. Well-meaning readers, not necessarily well-versed in local amphibians, could, with all the best intentions, come across Western Toads and, believing them to be the invasive Bullfrog, remove them in the mistaken belief that they are helping to promote an important native species. With this in mind, we bring our “Museum news” series to a close for the year with an attempt to cultivate a better appreciation of these two species, their identifying characteristics, and the unique roles they each play in our local ecosystems.

As it is the species that stands to gain and/or lose the most from this recent media attention, we’ll begin with the Western Toad, the only native toad on Vancouver Island. Much the same as other amphibians, the seasonality of the Western Toad has it overwintering on land, burrowed in forest floors or beneath logs. For much of the early spring and late summer/fall, their behaviour is poorly understood, although locally they are believed to be living and feeding in densely wooded environments. They are most visible in the early to mid-spring when they make their ways to lakes, marshes, and other wetlands to find mates and lay their eggs. This behavior changes slightly year to year, and is believed to be tied to both air temperatures and day lengths, but for the most part begins in mid-March to early April on southern Vancouver Island. For the most part, eggs will have been laid and adults will have retreated back to the woods by mid- to late April.

The Western Toad can be identifid by its bumpy skin and prominent dorsal line. Photo by J. N. Stuart
The Western Toad can be identifid by its bumpy skin and prominent dorsal line. Photo by J. N. Stuart

The main distinguishing factors that set the Western Toad apart from other frogs in the region are colour and skin patterns. As with many of the other amphibians, their colour scheme varies considerably with region, but generally their thick, knobbly skin ranges from dull to dark green or brown, is covered in dark or reddish glands, and has a dry appearance. Adult toads display a pronounced dorsal line, a light-coloured streak from their head down their back. Just aft of the eye is an ovular paratoid gland, and its legs are short and stalky compared to other frogs. Excluding the hind legs, the Western Toad grows to be roughly 5-15cm long. Females are larger than males, sometimes substantially so. Being one of the top consumers of various insects, the Western Toad plays an important role in many forest ecosystems. Adult toads are credited with keeping many different insects at a level that is healthy for trees and other plants. Without the toads, many plant species would endure huge stress.

The second species we need to look at, and the critters that really are a cause for concern, is the American Bullfrog. Originally native to the Canadian and US east coast, the Bullfrog’s territory has steadily (through introduction and natural dispersal) extended to cover most of continental North America, including much of south-eastern Vancouver Island and the lower mainland. Because they will feed on whatever fits into their mouth—often with over-the-top aggression—it has been observed that the Bullfrog out-competes native amphibians for space and resources in many situations, making it one of the biggest threats to native amphibian populations. Bullfrogs are also vectors for different fungal infections, further stressing local amphibian populations.

Known to breed prolifially, the American Bullfrog can produce up to 20 thousand eggs at once. Photo by Andrew C.
Known to breed prolifially, the American Bullfrog can produce up to 20 thousand eggs at once. Photo by Andrew C.

One easy way to identify the American Bullfrog is by its size. No other frog on Vancouver Island reaches the sizes that these creatures do; females grow longer than 20 cm (not including legs), with males slightly smaller. There are other identifying factors as well. While both exhibit similar general colours (dark-to-pale greens and browns), the lumpy glands found all over the Toad’s backs, heads, and legs are absent in the Bullfrog. Instead, Bullfrogs have more speckled legs, cream-coloured or yellow under- necks, and bright yellow eyes. Their skin also appears smoother and more moist than the Toads’.

There is quite a bit of concern surrounding the introduction and expansion of the American Bullfrog’s range, and the effect that they are having on various local ecosystems. Ongoing research studies on Vancouver Island and elsewhere in BC are attempting to get a better idea of the distribution and abundance of the Western Toad. This information is crucial to proper management of the species. While there are certainly still unknowns about both species and what their presence in certain areas means, there are a number of things that anyone can do to aid in the conservation of native species and to help the general understanding of these populations:

  • Report sightings of the American Bullfrog to local authorities or government groups, such as the BC Frog Watch Program.
  • Whether native or introduced, all amphibians are protected by the federal wildlife act against moving, containing, and transporting. Do not ever transport frogs or toads from one region to another. People bringing the Bullfrog from place to place for pets, or as garden features, may be one of the biggest factors responsible for their rapid expansion.
  • Establish and maintain desirable amphibian habitats. On top of invasive species such as Bullfrogs, one of the main threats facing many of BC’s amphibians is habitat loss. Take special care around these habitats, and if there are any wetlands and riparian areas on your property containing native species, do not use any lawn or garden pesticides or chemicals.

For more information on the American Bullfrog, the Western Toad, and the many other wonderful creatures that live around southern Vancouver Island, come by VIU’s Museum of Natural History. The museum is open to students and the public on Mondays from 10:30 am to 12:30 pm, Tuesdays from 1:30 to 2:30 pm, and Thursdays from 11:30 am to 1:30 pm. More information is available on their Facebook page and website.

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