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Scientific name: Bufo americanus
Common name: 
American Toad

(Information in this Species Page was compiled by Bobby Galonski in Biology 220W, Spring 2003, at Penn State New Kensington)

Bufo americanus is a very common, nocturnally active species of toad. It is found throughout almost all of the United States east of the Rocky Mountains, and its range extends north into central Canada and south into Mexico. It abundantly occupies both natural and human modified habitats. Its ubiquity has led to its informal designation as the “common toad.”

Appearance
Adult B. americanus are 2 to 4 inches long with females being slightly larger than males. They have stout, rounded bodies, and relatively short legs. Their skin is rough and thick with colors ranging widely over many shades of brown, dark-red, or dark-green. The toads are darker dorsally (on the back) than ventrally (on their bellies).  Males have a dark brown to black throat while females have a lighter (predominately white) throat coloration. Over the skin surface are a variety of spots and streaks of brown or beige. Dark brown spots on their backs typically contain one or two red and/or yellow, prominent, raised areas called “warts.” The number and patterning of these warts is important in the determination of many of the B. americanus sub-species.

Activity and Life Span
This toad is active from April to November depending upon the local climate and weather conditions. During their active seasons, they typically spend the day-light hours in their shallow soil burrows or under logs or within leaf piles. They emerge at night to actively feed on a wide variety of insects. The inactive seasons are spent in deeper, hibernation burrows that they dig into the soil profile.

In their natural habitats most American toads live for a year or significantly less. Successful (or lucky!) individuals, though, may live for 5 to 10 years in natural ecosystems and are thus able to reproduce (sexually maturity occurs after 2 to 3 years). In captivity, American toads are known to live much longer. One captive individual, for example, lived for 35 years before its unfortunate accidental death.

Diet and Economic Impact
Bufo americanus’ main tool for food gathering is its tongue which is long, sticky, and rapidly extensible. The attachment of the tongue inside of the lower jaw facilitates its rapid extension toward prey. B. americanus’ visual acuity, total visual fields, and large, binocular visual fields (for 3-D vision) contribute significantly to the efficiency of prey detection and capture. Prey items readily taken by B. americanus include flies, crickets, locusts, grasshoppers, bees, wasps, beetles, spiders, caterpillars, earthworms, slugs, and snails. It is estimated that 88% of their prey are invertebrates that are classified as agricultural pests. In a three month season, a single toad will consume just under 10,000 insects and, thus, has a significant economic value for farmers and gardeners.

Capturing Prey and Avoiding Predators
The American toad very rapidly orients itself to moving prey. If the prey is two inches or less away, the toad will remain motionless and use a rapid tongue extension to capture the organism. If the prey is more than two inches away, the toad will move via a “leap-sit-leap-sit” pattern into its striking distance.

Many predators would be expected to find B. americanus an ideally sized prey choice. Relatively few predators, though, readily take American toads for food. Its cryptic coloration, ability to change colorings to match substrate, and its avoidance of daylight and even moonlit nights all contribute to the excellence of its camouflage. Toads are also able to “play dead” upon encountering a predator thus possibly confusing the predator’s instinctive behaviors and potentially, then, avoiding being consumed. Also, the production of poisonous cutaneous secretions and parotoid gland (two glands located on the head just behind the eyes) poisons make the American toad a less attractive food item than might have been originally suspected. Garter snakes (which may have a resistance to the toad toxins), hognose snakes, hawks, herons, and raccoons are predators of adult toads. Eggs and tadpoles are preyed upon by a variety of fish, diving beetles, and predaceous diving bugs. It is interesting that toads raised in captivity do not, apparently, produce the parotoid and cutaneous toxins. It is suggested that the absence of the diverse array of arthropod-generated poisons in the diet of these captive toads is the explanation for this observation.

Breeding and Reproduction
The American toad breeds during a very short interval of only a few days in the spring. Breeding occurs in lakes, ponds, and marshes, but is especially common in flooded areas (wet meadows, puddles, and ditches) formed from the runoff accumulation of spring rains. Males congregate in these pools and make their trilling, mating calls both day and night while sitting half-submerged in the water. A number of males may be in residence even at a relatively small pool. There does not seem to be aggressive, territorial behaviors among these individuals. When a male does attach himself to the back of an attracted female (“amplexus”), the pair sits quite motionless in the shallow sections of the pool. The stillness of the pair is thought to help them avoid detection by other, non-paired males who might interrupt the mating event. The size relationship between the amplexic male and female is important. The smaller male must be small enough to ensure that his released sperm effectively fertilizes the ovulated eggs, but not so small that he leaves room on the female’s back for another, competing male. The eggs are released in strings which, as they are fertilized, are interwoven around the substrate and vegetation of the pool. The preferred selection of pools that do not have fish and the egg counter-shading (light on top and dark on the bottom) help to reduce the magnitude of egg predation.

Development of Young
Fertilized eggs develop quickly depending upon the temperature of the pool water. The eggs hatch in 3 to 12 days, and, as the tadpoles emerge, they form school-like groups called “aggregations.” These aggregations feed on algae, detritus and, possibly, protists and small invertebrates and grow and develop rapidly. Between days 12 and 20 the tadpoles (which are approximately one inch long) begin to form hind legs. After about two weeks more, the front legs will begin to be observed in some individuals. The eruption of the front legs signals the closing of the gills. After 35 to 70 days, then, the tadpoles mature into tiny, terrestrial toadlets. The wide range of timing for individual metamorphosis has logical ecological and evolutionary benefits. Avoidance of mass emergence (and possibly mass predation) and the maintenance of incubation flexibility in the face of highly variable spring rains (and pool size and, thus, pool longevity) are two keys aspects of the developmental biology of B. americanus.



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