Rhinella horribilis

Do not adjust your screen! Your eyes do not deceive you and NO, this picture was not doctored! Welcome to the world of the Giant Marine Toad, Costa Rica's largest amphibian. A predator nothing short of extreme.

These pictures were taken in early December 2006 during a Night Tour. We were wrapping up the evening when we came across this grizzly scene. A Marine Toad no larger than 12 centimeters swallowing a 30 centimeter Sock-headed Snake (Enuliophis sclateri). As we approached we startled the toad and he partially regurgitated the still living, still squirming snake.

Seconds later, as it grew accustomed to our incredulous stares, it proceeded to engulf the helpless snake. The whole process took about 15 excruciating minutes, leaving the toad bloated to the point of catatonia and seemingly unable to hop away to save its own life.

Giant Marine Toads are, without a doubt, noteworthy predators. With adult females reaching weights of 1.5 kilograms and measuring up to 240 millimeters they are a menacing presence. Individuals don't get quite that large in Costa Rica and adult females normally reach their maximum length at 175 millimeters. Nevertheless, several guests on the Night Tour have confessed to having mistaken them for garden ornaments.

Giant Marine Toads are opportunistic sit-and-wait predators. Prey items may include insects, spiders, small frogs and reptiles, mice, rats and pretty much any other small animal it can stuff into its mouth. It is in the vicinity of homes with house pets where you find the very large ones. Not necessarily because they eat the house animals, although they have been known to eat kittens, but because they have learned to feed on canned and dry pet food. This is a remarkable accomplishment for the toad because in nature they don't normally eat inanimate objects.

These are the notorious Cane Toads, reviled the world over by most of those obliged to share their homes with them. Although they are native to Costa Rica, they have been exported throughout the world and have become a rather cosmopolitan species.

It is now considered that Giant Marine Toads have adapted to life amongst humans and to our disturbed habitats even better than their natural habitats. Population samples in some agricultural areas have been estimated at an astonishing 300 toads per hectare! Meanwhile, scientists calculate Marine Toad populations living along forest edges at about 10 toads per hectare and those living in natural open areas at about 25 toads per hectare.

Although these behemoths are now widely considered pests this was not always the case. Giant Marine Toads were willingly imported by people throughout the Caribbean Islands and into the Philippines, Hawaii, New Guinea, Australia and Florida. This was done in a failed attempt to control insect pests in sugarcane plantations. Many of the areas they were imported into left the toads with no natural predators and populations exploded. The voracious toads then proceeded to devour every native species they could catch. This has seriously depleted diversity in many areas.

In Australia it's impact is not only environmental, but also economical. There, Giant Marine Toads use waterways to breed and large numbers of them also die there. Decaying toads and their toxic eggs contaminate water sources used by herds of sheep and cattle. This kills the animals, leaving ranchers to count their losses.

In regions where they are native, Marine Toads are preyed upon by a variety of reptiles, birds, and mammals. They are afforded some protection from predators by the two large toxin glands located behind their eyes. When disturbed, Giant Marine Toads can spray the toxin from their glands a distance of up to 30 centimeters and a cat or dog could easily die by simply mouthing it. Rainforest mammals like Opossums, Raccoons, and Coatis have been observed flipping the toads over and starting their meal through the toad's soft stomach, thereby avoiding the toxins.

The toxin is a milky liquid garnished with a chemical named Bufotenidine. This substance has been attributed hallucinogenic properties and is said to have effects similar to LSD. Some turn to the Marine Toad searching for a psychedelic trip via toad licking. This activity should always be avoided. Other symptoms, apart from the hallucinations, may include hypertension, constricting blood vessels, overly powerful heartbeat, and could culminate in a direct poisoning of the heart muscle.

During their mating season males congregate in breeding areas. These are usually located near slow moving streams. Calling males will sit partially submerged at the edge of the water and call out to the females. If a male successfully attracts a female, mating will take place while they are in the water.

The eggs are attached to two strings and covered with toxic jelly. The female toad will wrap the strings around vegetation growing from the bottom of the breeding pool to anchor them. The eggs develop for three to four days days before hatching and tadpoles will complete their metamorphosis in sixty to seventy-five days. After the little toads emerge from the water, the pace of their growth is tremendous. Males will reach close to their maximum size the first year of their lives, while the larger females will grow for four to five years. Giant Marine Toads have been known to live as long as 16 years in captivity.

References:

Janzen, D.  1983  Costa Rican Natural History  University of Chicago Press

Leenders, T.  2001  A Guide to Amphibians and Reptiles of Costa Rica  Zona Tropical

Savage, J.  2002  The Amphibians and Reptiles of Costa Rica   University of Chicago Press