Creature Feature: Fowler’s Toad (Bufo [Anaxyrus] fowleri)

i May 15th 1 Comment by

Creature Feature

Fowler’s Toad (Bufo [Anaxyrus] fowleri)

by Jeff Beane

Childhood is a toad in the garden, a happy toad.

–William Carlos Williams

For naturalists in the North Carolina Piedmont, April is a pretty fine month.  Spring is in full swing, filled with the sights and sounds of many things happening at once.  If you live near almost any sort of pond or wetland, a harsh, nasal “waaaaah!” will be just one of the sounds you can welcome at this time each year.  It means another breeding season is beginning for Fowler’s Toad (Bufo [Anaxyrus] fowleri).

The word “toad” has no precise scientific definition—it’s a general term used for anurans that tend to have chunky bodies and dry, warty skins; that hop rather than leap; and that are encountered more often on land than around water.  There are actually many families of anurans (Anura, literally meaning “tailless,” is the amphibian order that includes all frogs and toads), and many of them contain members commonly called toads.  The toads that most folks are most familiar with belong to the large family Bufonidae—the “true toads.”  Fowler’s toad is the most widespread, and perhaps the most frequently encountered, of North Carolina’s four bufonids.  It ranges throughout the Piedmont, much of the northern and inner Coastal Plain, and lower elevations in the Mountains.  The American Toad (B. [A.] americanus), is more common in the Mountains, but also ranges throughout most of the Piedmont and the northern Coastal Plain.  The Southern Toad (B. [A.] terrestris) occurs throughout most of the Coastal Plain.  The tiny Oak Toad (B. [A.] quercicus) is also a resident of the Coastal Plain, where it has undergone sharp declines in recent years.

Recent genetic work on bufonids has prompted some systematists to “split” the once-huge genus Bufo into several genera, and North Carolina’s four species have been recently assigned to the genus Anaxyrus.  But taxonomy is a controversial science, with much subjectivity involved, and published changes are not always immediately or unanimously accepted.  It will be a long time before some of us old-timers stop using names we’ve known our entire lives.  As my friend Dave Stephan put it:  “I will stop using the names Rana [a common frog genus] and Bufo when they are pried from my cold, dead hands.”

Bufo is Latin for “toad.”  Anaxyrus is from the Greek ????, meaning “sovereign” or “king.”  The species name honors Samuel Page Fowler (1799-1844), New Jersey statesman, member of U.S. House of Representatives, and mineralogist (the mineral Fowlerite is also named for him).  Fowler’s toad was until fairly recently regarded as a subspecies of the Woodhouse Toad, B. [A.] woodhousii.  The two are now recognized as separate species.

Fowler’s Toad is easily and often confused with the American Toad and Southern Toad—the three are similar in appearance and occasionally hybridize where their ranges overlap.  Usually no more than two of the three occur together in any one locality.  Around the greater Raleigh area, we have Fowler’s and American toads, with Fowler’s being slightly more common (see chart below for ways to distinguish these two).  Southern toads may enter extreme southern Wake County.

Toads are strictly carnivorous, and will feed on almost anything small enough to catch and swallow.  Prey items must be swallowed whole; toads are not capable of chewing or biting off chunks.  Small prey are snapped up with a quick flick of the toad’s sticky tongue.  A toad may use its forelimbs to help shove larger items down its throat.  The great majority of the diet is insects, but toads will also eat other arthropods, worms, and small vertebrates; the only things they don’t manage to get down are those packing a very powerful wallop via stings, bites, or harsh chemical defenses—and even some of these may elicit repeated attempts at being swallowed before the toad gives up.  They have strong stomachs and manage to eat some fairly noxious prey items.  Virtually all farmers and gardeners know of toads’ well-deserved reputations as insect control agents and welcome them in yard, field, and garden.  Toads may be active day and night, but are more often nocturnal, especially in hot weather.  They may gather at outdoor lights at night to eat the insects that accumulate there.  Such “porch light toads” often become tame, and many a child has made a game of tossing insects to a backyard toad.  Toads detect prey visually, by motion, and will attempt to feed on virtually any small moving object.  A toad surrounded by fresh dead insects would starve—they are not noted for their intellect.

Toads and other amphibians absorb water through their porous skin; they do not “drink” in the same fashion as do most mammals, birds, and reptiles.  A Fowler’s Toad’s skin is thicker and drier than that of many amphibians, allowing it to live its entire adult life on land.  Toads must remain at least somewhat cool and moist, however, and will seek underground refugia in hot or dry weather.  They also spend the colder months belowground.  A toad breathes mostly through its lungs, but some oxygen exchange also takes place through its skin.

Like a great many amphibians, toads produce skin secretions that make them unpalatable or even toxic to many predators.  Nonetheless, they are eaten by many animals whose stomachs can neutralize the toxins.  The Eastern Hognose Snake specializes on toads, eating very little else, and some other snakes, including garter snakes and Red-bellied Water Snakes, can eat toads with impunity.  Snapping Turtles also eat them.  Raccoons, skunks, crows, and some other predators may eviscerate toads, eating only the nutritious liver and other internal organs and leaving most of the carcass.  Newly transformed toads, besides being smaller, have milder toxins; they have many more predators than do adults.  Birds such as grackles and jays have been observed eating large numbers of toad metamorphs.  The biggest threats by far, however, are humans with their vehicles, mowers, domestic animals, and pesticides.  But even the killing of huge numbers of individual toads by these factors pales in comparison to outright loss and fragmentation of habitat.  Still, the adaptable Fowler’s Toad manages to survive in some suburban and semi-urban areas, as long as there is a place to breed and some terrestrial habitat.  Its adaptability has allowed it to remain common in the face of serious declines among other amphibian species.

Like all of North Carolina’s anurans, Fowler’s toads must breed in water.  They utilize a great variety of wetlands for breeding, from puddles to lakes and rivers.  They readily use permanent water, and the construction of farm ponds, reservoirs, and other artificial bodies of water has probably greatly benefited them.  Their tadpoles, unlike those of many amphibians, are tolerant of fish; they avoid them by staying mostly in very shallow water, by hiding in vegetation or bottom litter, and by being bad-tasting.

In the Raleigh area, Fowler’s Toads usually begin calling around the first week of April, but that varies with temperature, water levels, and location.  The breeding season is prolonged, often lasting until July or August.  Males call to attract females and to maintain territories (females are silent).  They may sit in shallow water or on land when calling.  Sound is produced by inflating the vocal sac and forcing air across its thin membrane.  Different frog and toad species have different types and shapes of vocal sacs.  A Fowler’s Toad has a single, spherical one that inflates like a balloon under his throat.  The call has been compared to the bleat of a sheep.  When a female approaches, a male grabs her and clasps her tightly just behind the armpits with his forelimbs.  This position is called amplexus.  He will hold onto her until she releases her eggs and will dump sperm on the eggs as they are laid.  Enthusiastic males may try to mate with other males, or with other amplexed pairs.  In extreme situations, males may form mating balls with a female or two somewhere in the middle; on rare occasion females, or even males, may be overwhelmed and drowned.  Males emit a chirping “release call” when clasped by another male.  The particular frequency of this call usually causes a male to realize his mistake and release his would-be mate.  Male toads will also utter this release call when handled, and this is a useful method of distinguishing the sexes; another is that males have dark throats while those of females are plain white.  Females also attain slightly larger sizes than males.

Fowler’s Toads deposit their eggs in long strings.  Two strings are produced simultaneously—one from each ovary—totaling around 7,000 eggs.  They are randomly strung in vegetation or on the shallow pond bottom.  The eggs hatch in about a week and the small, black tadpoles grow quickly, feeding mostly on algae and other organic material, which they scrape from the substrate with the keratinized rows of teeth lining their small mouths.  They transform in about one to two months at small sizes—newly transformed toads are only about 0.3-0.4” (8-11 mm) long.  They can be found leaving ponds in huge numbers.  They may disperse far from the wetlands, and will immediately begin eating insects and growing rapidly. Some may reach sexual maturity in as little as a year, while others require two or three years.  They will live the rest of their lives on land, except for returning to ponds or wetlands annually to breed.  Only a tiny percentage of the thousands of eggs laid by a female toad will end up as breeding adults.

For defense, toads rely on cryptic behavior (hiding, camouflage), on flight (hopping quickly away toward cover); and on their skin toxins.  Rough handling can result in a toad exuding its milky-white toxins—called bufotoxins.  These are produced in various places in the toad’s glandular skin, but especially in the two large, oval glands located on each side of the head—the parotoid glands.  Bufotoxins may have hallucinogenic properties in small quantities.  Some species of toads—most often the Sonoran Desert Toad (Bufo [Incilius] alvarius) and the Marine Toad, or Cane Toad (B. marinus [Rhinella marina])—are actually abused as a drug; live toads are licked, or their skins are dried and eaten or smoked.  Some Native American tribes are known to have dried toad skins and smoked them ceremonially.  Such activities can, of course, potentially result in severe vomiting, brain damage, or death.  North Carolina’s toads have relatively mild toxins and are more likely to induce instant vomiting in a human than either hallucinations or death.  They are harmless to human skin, but can cause severe irritation if rubbed in the eyes or other mucous membranes.  In other words, toads may be safely handled, but don’t eat or lick them, or rub your face or any other sensitive part of your body with them.  Needless to say, they do not cause warts.

A frightened toad will also inflate its body with air to make it larger and harder to swallow, and will release excess water (this is not urine, as is commonly believed) from its cloaca.  Toads may also feign death when handled.  This might seem like self-defeating behavior, but a toad that is swallowed by a snake without a struggle sustains no injuries, and just might survive if the snake happens to regurgitate it later because of its skin toxins or for some reason.

Potential longevity is poorly known for most toad species, but some bufonids have lived for longer than 20 years in captivity.  It seems reasonable that a Fowler’s Toad could live for 10 years or more in the wild if it could escape predators for that long (very few do).

Watch for Fowler’s Toad in your yard or garden this spring, and listen for its harsh-but-friendly voice on spring and summer nights.  As neighbors go, you could certainly do worse.

Fowler’s Toad                                                                                 American Toad

Most dark spots on back will each contain 3 or more warts. Most dark spots on back will each contain 1 or 2 warts.
Cranial crests (bony ridges on top of the head behind each eye) are small and inconspicuous. Parotoid gland (large, oblong gland on each side of the head) is usually flush against cranial crest. Cranial crests are well-developed and conspicuous.  Parotoid gland is usually separate from cranial crest or connected by a short spur.
Smallish warts on outer surface of tibia or shank of hind leg. Enlarged warts on outer surface of tibia or shank of hind leg.
Underside usually plain white with a single dark spot on chest/throat. Chest often mottled with dark pigment; usually no single dark spot.
Smaller; maximum snout-vent length about 3.25” (82 mm). Grows larger; maximum snout-vent length about 4.25” (107 mm).  Largest specimens are from Mountains.
Snout slightly more pointed. Snout slightly more broadly rounded.
Color highly variable, but sometimes greenish. Color highly variable, but usually brown, gray, or reddish; seldom looks greenish.
In Raleigh area, usually calls from early April to August. In Raleigh area, usually calls from late February to April.
Call is a harsh, nasal “waaah,” ca. 1-4 seconds in duration. Call is a long, musical, whistlelike trill, ca. 20-30 seconds in duration.
Breeds in a wide variety of wetlands, but often prefers farm ponds, lakes, or other permanent water. May use permanent water, but prefers woodland pools or other temporary wetlands.
Tends to have slightly lower, more horizontal posture and slightly smaller forelimbs. Tends to sit more upright; forelimbs slightly larger.
Usually a distinct whitish mid-dorsal stripe. Mid-dorsal stripe often present, but not always distinct; sometimes faint or absent.