Florida’s Invaders–Cane Toad

The Cane Toad, from South America, is the largest toad species in the world. It also packs a wallop–the poison produced in the toad’s paratoid glands are powerful enough to kill dogs.

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In the early 1920’s, the US Army Corps of Engineers, at the request of Florida’s state government, began a massive decade-long program of excavation and drainage, digging a number of criss-crossing canals to drain away the Everglades and turn the “worthless swampland” into productive agricultural area. One of the people attracted to the new land was Charles Stewart Mott, a former General Motors executive who now owned the US Sugar Company. US Sugar set up plantations all over south Florida, encouraged and supported by generous tax breaks and subsidies from the State and Federal governments, and other sugar companies soon followed. In the 1930’s, “King Sugar” quickly came to dominate the state, economically and politically.

But the industry had difficulties. Sugar cane does not grow naturally in Florida, and the climate is not really suited for it. As a result, the sugar plantations required massive amounts of fertilizers to keep the cane alive. The plantations were also infested with insect pests, and chief among these were the “white worms”, the grub larvae of several species of scarab beetle. In 1932, the sugar industry in Hawaii had faced the same problem, and dealt with it by “natural pest control”–they imported 150 Giant Toads from South America (then known as Bufo marinus, now known as Rhinella marina) and released them, hoping they would eat the beetles and control the larvae.

The Giant Toad, also known as the Marine Toad or the Giant Bufo (and now known worldwide as the Cane Toad) is the largest species of toad in the world. It is found mostly in South and Central America, though native populations reach through Mexico into the southern part of Texas. In the southern tropical parts of its range the toad can reach sizes up to a foot long and weigh as much as 5 pounds. In the northern extremes of their range (Texas and Florida) they get about half that size. Voracious feeders, they will swallow anything that moves that is smaller than they are.

By 1938, the toads had also been introduced into sugar plantations in the Caribbean, Louisiana, Puerto Rico, the Philippines, Australia and New Guinea. In 1936, it was Florida’s turn. The University of Florida obtained 200 Giant Toads from Puerto Rico and released them at its Agricultural Experiment Station in Palm Beach County. The experiment failed when nearly all the toads died. So a few years later, two sugar companies in Glades County and Dade County tried again, releasing several hundred toads. Alas, the toads did not make any significant impact on the beetle populations, and most of them died out too. The sugar industry gave up, and used a plethora of pesticides on its cane fields instead.

In 1955, however, the toads got a lucky break. A shipment of Cane Toads that had been imported from Colombia was sitting on the tarmac at Miami Airport when the crate was accidentally broken open, and 100 toads went hopping off to freedom. This time, the population managed to establish itself. In 1958, a new canal was dug which connected the breeding ponds being used by the toads to the rest of South Florida’s extensive canal system, and the toads were free to move. By the 1970’s they had covered most of southern Florida, and by the 80’s they had reached Tampa Bay.

The toads proved themselves to be remarkably adaptable, and soon settled in for an easy life in suburbia. Streetlights and lawn lamps provided them with plenty of food; they laid their long string of thousands of eggs in fish ponds and drainage ditches. (As the name suggests, the Marine Toads are also more tolerant of salt water than most amphibians, and can lay their eggs in brackish estuaries and tide swamps.) The huge paratoid glands on the back of their necks produced a milky white toxin that was powerful enough to kill dogs and protected them from predators–even the eggs are toxic, and kill tadpoles of other frog species that eat them. And unlike most toads, who will only eat live prey that is moving, the Cane Toads learned to eat dry dog food out of dishes, opening up an enormous source of suburban food.

Today, the Cane Toad is one of the most invasive species on the planet. Not only is it thriving in many of the agricultural areas where it was deliberately introduced, but it is also found in the exotic pet trade. In Australia, it is a major threat to rare native species of marsupial, particularly predators who try to sample the toads and end up getting poisoned. In Bermuda, the Cane Toad is a known threat to the severely endangered Bermuda Skink. In Florida, the invaders are displacing the native Southern Toad, and several thousand dogs and cats are killed each year when they bite the toad or pick it up in their mouths. (Many of our native raccoons and opossums, however, have learned to eat the toads by flipping them onto their backs and eating out their stomachs, leaving behind the toxic glands on the toad’s back.)

The Cane Toad, meanwhile, is continuing its slow northward invasion. It now reaches as far north as Pasco County, and there appears to be nothing to prevent them from eventually reaching as far as Georgia and perhaps the Carolinas. Within Florida, the Fish and Wildlife Commission has more or less given up on attempting to control the species, though it urges Florida residents to kill the toads wherever they are found.

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Forgotten mysteries, oddities and unknown stories from history, nature and science.