Cane toads on Sanibel, Captiva
It is that time of year again when it is slowly starting to warm up and any out-of-season rainstorms can trigger amphibian breeding. On Sanibel, this is limited to frogs and toads as we do not have any salamander species on the island. Besides the southern leopard frog (Lithobates sphenocephalus) which is our sole true winter breeder, the southern toad (Anaxyrus terrrestris) and the giant toad aka cane toad (Rhinella marina) are the usual suspects for late winter/early spring breeding, especially after a heavy rain.
The southern toad is native and too often confused for the invasive exotic giant toad – the cane toad – in our area. Giant toads go by several local names, depending on where you are located. In Florida, the most common names are cane toad, faux toad, or Bufo toad. Outside Florida, many people call them marine toads. The local name “Bufo toad” comes from the former scientific name (Bufo marinus). In 2008, the cane toad was split off into a new group of South American beaked toads (Rhinella). The current name is Rhinella marina. They are native to extreme south Texas to South America. They were introduced in many countries around the world in an attempt to control insects in sugarcane fields, a failed experiment.
Cane toads were discovered breeding in an isolated area on Sanibel in 2013 near Fulgur Street and Middle Gulf Drive during annual frog call surveys conducted by the Sanibel-Captiva Conservation Foundation and and the J.N. “Ding” Darling National Wildlife Refuge. All 10 breeding adults were removed from a small wetland, but the damage was already done: eggs had been deposited. From there, cane toads used the beach to move westward down the island and eventually to move across the whole island. They are now all the way to South Seas Plantation on Captiva (yes, they hopped across the bridge at Blind Pass).
It is unknown how they originally got to this area on Sanibel, but it is likely that juveniles (tadpoles or toadlets) were accidentally brought in by way of potted plants, sod, fill dirt, or mulch in that area. They were certainly localized to that area in the beginning as they were never reported by anyone (by way of pictures, roadkill, or even hearsay) and were never documented anywhere in frog call surveys. The young toads likely grew to adults and waited for the right opportunity to breed. When water levels rose to the right height to fill in temporary wetlands, the toads bred and that is when they began to expand their range.
Cane toads are large, reaching 4-6 inches in length (not stretched out) as opposed to southern toads that are typically 2-3 inches in length. Cane toads have enlarged parotoid glands behind the head that carry a toxin called bufotoxin that is very potent, especially to smaller animals like dogs, cats and native wildlife. They are not aggressive, but will ooze this toxin out of the glands if they are threatened, such as being picked up in a dog’s mouth. Our native southern toad is often mistaken because of their similar “toad-like” features. However, southern toads have small parotoid glands, cranial crests (ridges) between the eyes and the head has a stouter profile. Cane toads have a more compressed head profile and ridges on the eyelids (like eyebrows) and are much larger on average. Newly metamorphized toadlets of these two species are mostly indistinguishable from each other.
Chris Lechowicz is a herpetologist and the wildlife and habitat manager at the Sanibel-Captiva Conservation Foundation. For more information, visit www.sccf.org.