The non-native marine toad, Bufo marinus, is the largest of Florida's frogs and
toads. It has a stout body and short legs, with the digits of the forelimbs
lacking webbing and those of the hind limbs being webbed. The skin is rough
and warty. Skin ranges in color from gray to tan to red-brown, dark brown, olive to
dull green, to black above, and cream-colored and often flecked with brown or
black on the belly. The tympani (ear membranes) are one-half to two-thirds the
diameter of the eyes (Ashton and Ashton 1988)
The most distinguishing feature (other than size) is the presence of two large
parotid glands, located at the shoulder behind each eye. These are venom glands
capable of producing toxic milky secretions when squeezed. Smaller venom
glands ('warts') are distributed all over the surface of the skin (Conant and
Collins 1991, Gautherot 2000).
Tadpoles are jet black dorsally and silvery white with black spots ventrally
(Ashton and Ashton 1988).
The vocalization of B. marinus is a slow, low-pitched trill and larger
males usually have deeper calls (Somma 2004).
Potentially Misidentified Species
The size of the marine toad and the presence of the large parotid glands and
webbed hind digits make this species easy to distinguish from other Florida
frogs and toads.
HABITAT AND DISTRIBUTION
Bufo marinus is a highly adaptable invader and where it occurs in Florida it is typically
found in agricultural and urbanized areas.
The native range of B. marinus extends from northern South America,
through Central America and Mexico, and up into southernmost Texas (Conant and
Collins 1991, Somma 2004).
The species is established in south Florida and around Tampa on the Gulf coast,
and they are also found on Stock Island and Key West (USGS/SEARMI). These populations are probably derived from
intentional introductions as well as accidental introductions in agricultural
products and from escapes of pets from homes and from the pet trade (Somma
Collection records indicate Bufo marinus occurs in at least three of six IRL watershed counties (Palm Beach,
Martin, Indian River, probably St. Lucie as well). It appears to be widely
established in Palm Beach and Martin counties. Smaller populations of B. marinus
pesist elsewhere in isolated pockets as, for example, an established population
reported in Vero Beach near Dodgertown in 2002.
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Bufo marinus in Florida can reach sizes of around 10-15 cm (and up to
nearly 24 cm elsewhere) and female toads can weigh up to 2.5 kg (Behler 1979,
Bufo marinus is considered to be abundant in Dade and in some areas of
Monroe Counties, occurring in lesser numbers elsewhere in south Florida
In Florida, Bufo marinus typically breeds in man-made habitats such as drainage
canals and ditches, fish ponds, temporary pools and other shallow water bodies
(Somma 2004). Breeding in Florida typically occurs during the wet season from
early spring into the fall, and typically occurs during or just after rain
events (Conant and Collins 1991).
B. marinus exhibits high fecundity with large females capable of
producing 20,000 eggs or more (Somma 2004).
Egg strings may be free-floating or wrapped around submerged as well as surface
material (Somma 2004). Eggs hatch into tadpoles at around three days and the
tadpoles metamorphose to juvenile toads around 45-55 days later (Krakauer 1970,
Ashton and Ashton 1988).
Marine toads are cold intolerant. Krakauer (1970) suggests that
cold-sensitivity had thwarted several past attempts to intentionally introduce
the species more widely in Florida.
Despite the scientific and common names, the marine toad is entirely
terrestrial as an adult outside of breeding. Eggs and tadpoles of Bufo marinus do exhibit a degree of salinity tolerance but only to
concentrations of around 5 ppt or so, roughly equivalent to 15% the salinity of
seawater (Ely 1944, Wright and Wright 1949).
Marine toads are voracious predatory omnivores that consume not only insects
and other arthropods but also molluscs, vegetation, and any other frogs or
toads they encounter. In urbanized settings, they will consume cat or dog food
if it is left out and they may also scavenge garbage (Alexander 1964, Cabrera
et al. 1996, Somma 2004).
Marine toads are primarily nocturnal and they often congregate around lights to
take advantage of the insects that they attract.
Marine toads have been repeatedly introduced throughout the world as a
potential biological control agent for crop-damaging insects, primarily those
that damage sugarcane (Krakauer 1968, 1970). The most infamous introduction is
the 1935 intentional release into the canefields of Queensland, Australia in an
unsuccessful attempt to control the sugar pest the greyback cane beetle
(Dermolepida albohirtum). The marine toads used in the
Queensland introduction were from Hawaii where the species had been
intentionally introduced just a few years earlier (McKeown 1996, Lever, 2001).
The first attempts at intentional introduction of Bufo marinus into
Florida occurred at approximately the same time as the Hawaii and Australia
introductions. Specimens imported from Puerto Rico were released into Palm
Beach County in 1936 but the species failed to become established on this
occasion and in two subsequent attempts as well (Krakauer 1968).
Marine toads finally did become established in Florida after an accidental
release by an importer in 1955 from the Miami Airport (Krakauer 1968, Ashton
and Ashton 1988). Additional intentional releases into south Florida in 1963 and
1964 facilitated establishment and subsequent explosive population growth. The
species was recognized as a nuisance species requiring control as early as 1965
(Krakauer 1968, 1970).
Potential to Compete With Natives
Marine toads likely compete with native species for food, living space and
breeding sites and may have, in some parts of the world, been a the
principal cause of local extirpation of some native amphibians (Krakauer 1968).
Marine toads also eat other species of frogs and toads and practically any
other suitably-sized animal they encounter.
Possible Economic Consequences of Invasion
The defensive secretions produced by the parotids and other poison glands are
highly toxic and are capable of killing dogs, cats, and other animals that bite
into or attempt to consume them (USGS/SEARMI). Effects on native fauna are not
fully known but are believed to be similar.
The secretions are also capable of making humans seriously ill, and of causing
serious skin and eye irritation Carmichael and Williams 1991, Conant and
Bufo marinus is listed by ISSG as as among "100 of the Worst" global invasive organisms, and authorities
consider it to be the "most introduced amphibian in the world" (Behler 1979,
Carmichael and Williams 1991).
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marinus (Linne). Herpetologica 20:255-259.
Ashton, R.E. and P.S. Ashton. 1988. Handbook Of Reptiles And Amphibians of
Florida. Part Three, the Amphibians. Windward Publishing, 191 p.
Behler J.L. 1979. The Audubon Society Field Guide to North American Retiles and
Amphibians. Alfred A. Knopf, New York. 743 p.
Cabrera J., Barrantes R., and D. Rodriguez. 1996. Habitos alimentarios de
Bufo marinus (Anura Bufonidae) en Costa Rica. Revista de Biologia
Carmichael P. and W. Williams. 1991. Florida's Fabulous Reptiles and
Amphibians. World Publications. Tampa, FL. 120 p.
Conant R., and J.T. Collins. 1991. Reptiles And Amphibians, Eastern/Central
North America. Houghton Mifflin Company. Boston. 450 p.
Ely C.A. 1944. Development of Bufo marinus larvae in dilute sea water.
Krakauer T. 1968. The ecology of the neotropical toad, Bufo marinus, in
south Florida. Herpetologica 24:214-221.
Krakauer T. 1970. The invasion of the toads. Florida Naturalist 1970:12-14.
Lever, C. 2001. The Cane Toad. The History and Ecology of a Successful
Colonist. Westbury Publishing, England. 230 p.
McKeown S. 1996. A Field Guide to Reptiles and Amphibians in the Hawaiian
Islands. Diamond Head Publishing, Inc., California. 172 p.
Somma L.A. 2004. Bufo marinus species profile. USGS Nonindigenous
Aquatic Species Database. Gainesville, FL. Available online.
Wright A.H., and A.A. Wright. 1949. Handbook of Frogs and Toads. Comstock
Publishing Associates, Ithaca NY. 640 p.