The World’s Largest Frog – Working with the Massive Goliath Frog

As a child, my information on the Goliath Frog, Conraua goliath, was limited to a few brief sentences hidden away in various books, but this was enough to spark my interest.  Eventually, a life-sized sculpture of one at the American Museum of Natural History (please see photo) gave me some idea of just how impressive a creature it was, and my desire to learn more intensified.  Happily, I found a job at the Bronx Zoo shortly after a group of Goliath Frogs arrived there from Cameroon, and I was able to indulge my passion.  One of my new charges spanned 25 inches with legs extended…nothing, not even the enormous African Bullfrogs and Marine Toads (or, for that matter, Leatherback Turtles!) that I had already handled prepared me for the sight of that amazing animal.

The Goliath Frog Exhibit

I first started working with Goliath Frogs in 1983, at which time we knew little about their natural history or captive needs. Unfortunately, not much has changed since, although field research completed in 1985 (Sabater-Pi, Contribution to the Biology of the Giant Frog, Amphibia-Reptilia, 6(2), 143-153) has filled in some of the blanks.

The new Goliath Frogs, collected as adults in Cameroon, were shy and high strung, and prone to wild, injury-producing leaps when disturbed. We assumed, therefore, that the zoo’s noisy, crowded Reptile House would not prove an ideal location for their exhibit. Therefore, the curator commandeered an exhibit at the relatively-ignored Aquatic Bird House. Goliath Frogs are habitat specialists, so their exhibit was arranged accordingly, and outfitted with a waterfall and a swift, rocky stream bordered by dense thickets of live plants. In keeping with what little information was available, the water was maintained at a slightly acidic pH.

Captive Behavior

The frogs settled in nicely, but, despite their size, one had to search long and hard to find them. Although wild adults reportedly bask in the sun, ours rarely left the water by day (I wonder now if UVB would have been helpful…please see below).  At night, however, they became quite active – prowling the shoreline and gobbling up Leopard Frogs, their favorite food. I watched them overnight on several occasions, and a bird keeper who lived in the basement of the building (long story!) also kept tabs on their nocturnal wanderings. Unfortunately, breeding behavior was never observed, and this seems to remain true today.

Although field research indicates that invertebrates form 60% of the Goliath Frog’s natural diet, those I cared for favored other frogs over all else.  I suspect that crayfish would have been accepted, but these were not regularly available back then.

Webbed Fingers and Toes

The frogs under my care were dark brown above (some field reports describe adults as greenish-brown, and juveniles as greener in color) and white, tinged with light yellow, below. The feet were fully webbed and tabs of skin fringed the fingers, perhaps to assist in swimming or grasping rocks buffeted by swift currents.

Natural History

Size

With a snout-vent length of 13 inches and legs of the same length, the Goliath is by far the longest of all frogs. It also vies for the title of heaviest, although African Bullfrogs and Marine Toads occasionally tie or even exceed the Goliath record of approximately 8 pounds. Considering how few have been accurately measured, even bigger individuals may be out there…if they are not eaten! (please see below).

Range and Habitat

The Goliath Frog occupies an 80 to 100 mile-wide range in Cameroon and the Republic of Equatorial Guinea, West Africa (please see map).  Within this tiny area, it is limited to swift, unpolluted, rocky streams bordered by dense equatorial rain forest.

Diet

Field studies are scarce, but indicate that invertebrates comprise at least 60% of the diet.  Freshwater crabs, spiders, scorpions, snails, beetles, millipedes and toads (2 species) have been recorded as prey

Goliath Frog tadpoles, which are quite “normal” in size, are believed to feed upon a single plant species for much of their lives.

Reproduction

Limited observations indicate that several hundred eggs are attached to aquatic vegetation in quiet pools among the rapids. The tadpole stage lasts for 2.5 to 3 months.

In common with certain other frogs that inhabit noisy, rushing streams, Goliath Frogs produce no mating calls. It is not known whether they communicate via body posture or hand signals, as do Panamanian Golden Frogs.

Behavior

Juveniles spend most of their time in the water, with just the head exposed. Adults sit on rocks within streams, often in direct sunlight, and seem to adjust their exposure to the sun by changing positions. This apparent basking behavior lasts for up to 35 minutes, after which the frogs spend some time in the water before returning to the rocks.

Goliath Frogs hunt along stream borders at night. There is some evidence that adults maintain distinct hunting territories of 60 to 130 square feet.

Conservation

Collection for the food trade is thought to be the greatest threat, especially now that traps have replaced capture by hand. Logging and stream siltation are also concerns. One recent study documented a 50% decline in the adult population over a 15 year period.

In years past, Goliath Frogs were exported for use in zoos, the pet trade and even frog-jumping contests. I recall seeing an individual that had been entered into one such contest in California. Given their high-strung nature, I was not surprised to note that its snout was bleeding and showed evidence of past injuries.

Goliath Frogs are classified as Endangered by the IUCN. Part of their range lies within Equatorial Guinea’s Monte Alen National Park, but information as to what protection this affords is difficult to come by.

 

Further Reading

Goliath Frog Video and Facts

Goliath Frog Photos and Information

Goliath Frog Field Study

Goliath Frog image referenced from wikipedia and originally posted by Ryan Somma
Zambian Landscape image referenced from wikipedia and originally posted by Florence Devouard