Couch’s spadefoot
(Scaphiopus couchi)

Order: Salientia
Family: Pelobatidae (spadefoots)
Other common name: spadefoot toad
Spanish names: sapo con espuelas

Distinguishing Features

Couch’s spadefoot is a 3 inch (8 cm), smooth-skinned, greenish, yellowish, or olive spadefoot with irregular blotches or spots of black, brown, or dark green. The belly is white and without markings. At the base of each hind foot is a dark, sickle-shaped keratinous “spade,” hence the name spadefoot. The width of the eyelids is approximately the same as the distance between the eyes. The pupils are vertical.

Though often called spadefoot toads, spadefoots are not true toads and should therefore simply be called spadefoots.

Range

In the southwestern United States, Couch’s spadefoots range from southeastern California through southern Arizona and southern New Mexico. They continue into all of Texas, except the extreme north and east, and northward to southwestern Oklahoma. In Mexico, this frog is distributed along eastern Baja California and on the western and eastern coasts of mainland Mexico south to Nayarit and southern San Luis Potosi.

Habitat

Couch’s spadefoots do well in extremely xeric (dry) conditions in areas with sandy, well-drained soils often occupied by creosote bush and mesquite trees. They are also found in short grass prairies and grasslands, cultivated lands, and along desert roadways during summer thunderstorms.

Life History

During summer monsoons, the spadefoot is well-known for emerging from its subterranean estivation to breed in the temporary ponds created by the heavy runoff. Interestingly, the cue for adult emergence during these summer thunderstorms is not moisture, but rather low frequency sound or vibration, most likely caused by rainfall or thunder. Upon emergence, males begin calling to attract females. Their calls sound like the bleating of sheep or goats. One female may lay as many as 3000 eggs. Once the eggs are laid, they must hatch quickly into tadpoles before these shallow pools disappear. And hatch quickly they do — at water temperatures of 86°F (30°C) eggs hatch in 15 hours! Tadpoles must also metamorphose quickly — 2 weeks on average, sometimes as little as 9 days — into froglets before the ponds dry up. In this exacting atmosphere very few eggs make it to young frogs.

Using the spade on the hind foot, spadefoots can quickly bury themselves in loose, sandy soil. Adult spadefoots burrow into the ground to avoid heat and desiccation, but recently metamorphosed spadefoots may be seen during and immediately after the rainy season in any moist place — under vegetation, former ponds, or moist soil. During this time young spadefoots need to eat enough food to survive the unfavorable living conditions above the surface of the ground. After eating as much as possible, they too burrow beneath the surface. Breeding may not occur in years with insufficient rainfall. Preying primarily upon beetles, grasshoppers, katydids, ants, spiders, and termites, a spadefoot can consume enough food in one meal to last an entire year!

Comments

Couch’s spadefoots have a skin secretion that may cause allergic reactions in some humans. Cuts and scratches may become painful, and sneezing and discharge from the eyes and nostrils may also result from the handling of this amphibian.

Sonoran Desert toad (Bufo alvarius)

Order: Salientia
Family: Bufonidae (true toads)
Other common names: Colorado River toad
Spanish name: sapo grande

Distinguishing Features

At 7 inches (18 cm) or more this is one of the largest toads native to North America. Adults have a uniformly green to greenish-gray dorsum (topside of the body) and creamy white venter (underside). Large white turbercles, or “warts”, are found at the angle of the jaw, but aside from the large parotoid glands and a few large lumps on the hind legs, this species has relatively smooth skin. Recently metamorphosed toadlets will be tan to green with orange or red spots on the dorsum. Unlike other male toads in our region, male Sonoran Desert toads do not have dark throats; males develop darkened, thick callosities (calluses) on the inside of the thumbs of the forelimbs during the breeding season.

Range

Found from Central Arizona to southwestern New Mexico and Sinaloa, Mexico; historically entered southeastern California, though it has not been seen there since the 1970s.

Habitat

This toad is common in the Sonoran Desert. It occurs in a variety of habitats including creosote bush desertscrub, grasslands up into oak-pine woodlands, and thornscrub and tropical deciduous forest in Mexico.

Life History

Sonoran Desert toads feed upon a variety of insects throughout their lives. Adults eat primarily beetles, although large individuals will occasionally eat small vertebrates including other toads. Sonoran Desert toads are active from late May to September, though principally during the summer rainy season. They are nocturnal during the hot summer months. The male’s call is weak, sounding somewhat like a ferryboat whistle. Eggs are laid in temporary rainpools and permanent ponds. Larvae metamorphose after 6 to 10 weeks. This species lives at least 10 years, and perhaps as many as 20 years.

Comments

Sonoran Desert toads have extremely potent, defensive toxins that are released from several glands (primarily the paratoids) in the skin. Animals that harass this species generally are intoxicated through the mouth, nose, or eyes. Dog owners should be cautious: the toxins are strong enough to kill full grown dogs that pick up or mouth the toads. Symptoms of intoxication are excessive salivation, irregular heartbeat and gait, and pawing at the mouth. If a dog displays any of these symptoms, use a garden hose to rinse its mouth from back to front and consult a veterinarian.

An Open Door Policy

Colorado River toads are impressive amphibians, the largest toads in the Sonoran Desert, with an equally impressive diet of insects, including the large palo verde wood borer beetles. Each summer we are regularly visited inside our home by some of these toads. One in particular visited us for five consecutive years.

The welcome sighting of this toad always indicated to us that the summer rains were due to commence almost immediately. He made his appearance in the house by entering through the flap-type dog door, after which he traveled about the house consuming any insects he found along the way. Eventually he arrived in the sun porch off our living room, where he plopped himself in the water of a fountain in the corner of that room. We are not sure, but believe that he hibernated one winter in the soil of a flowerbed adjacent to the fountain.

It has been several years since we last saw this, our favorite toad, but others of his species visit us each summer.

— Bill Woodin, ASDM Director Emeritus & Beth Woodin, ASDM trustee

Sonoran Green Toad (Bufo retiformis)

Order: Salientia
Family: Bufonidae (true toads)
Other common names: reticulated toad
Spanish name: sapo

Distinguishing Features

The Sonoran green toad is small, reaching only 2½ inches (57 mm) in length. Brightly colored, this toad is green to greenish-yellow with reticulations (net-like lines) or spots of black or brown on the back and legs, and numerous small, black-tipped warts on the back and sides. The underside is white with an occasional speck or two of black. The parotoid glands are large. Males have a dark throat.

Range

Endemic to the Sonoran Desert region, this toad is found from south-central Arizona to west central Sonora.

Habitat

The Sonoran green toad is found along washes in mesquite grasslands and creosote bush flats between 500 and 1500 feet (150 to 450 m).

Life History

Once the summer rains begin, males move into grasses around temporary rainwater pools and washes and begin to call. The call lasts a few seconds and sounds like a combination buzz and whistle. Hatchlings are only J inch (3.5mm) in length — smaller than a pea!

Comments

Male Sonoran green toads, like all Bufo species, have rudimentary ovaries that can become functional if the testes are damaged or removed.

A Time for Toads

Toad and spadefoot activity is highly correlated with the monsoon season. Some species may be active as early as late spring while others will be out only after summer rains. If it is cool enough, desert amphibians may occasionally be active during the day. However, most species are primarily active at night when one often hears the strange calls of males from quite a distance. Some sound like bleating sheep, others chirp, snore, or wheeze; some make almost no sound at all.

Red Spotted Toad (Bufo punctatus)

Order: Salientia
Family: Bufonidae (true toads)
Spanish name: sapo

Distinguishing Features

This small, up to 3 inch (76 mm) long toad has round parotoid glands, a characteristic which distinguishes it from other toad species in the region. It tends to be whitish when found in association with limestone, light tan to red around volcanic rocks, to brown above, with scattered reddish tubercles (raised bumps); the underside is creamy white. Males have dark throats and single vocal sacs. The body and head are dorso-ventrally compressed, giving this toad a flattened appearance.

Range

This toad is found from southern Nevada to southwestern Kansas, south to Hidalgo, Mexico, and throughout Baja California. It occurs from below sea level up to 7000 feet (1980 m).

Habitat

A riparian inhabitant, this species is commonly encountered in and around rocky streams and arroyos. Its flattened body allows it to wedge into narrow rock crevices.

Life History

The red spotted toad is insectivorous. It breeds mainly after summer rains in quiet pools. The call of the male is a high-pitched musical trill, which may be confused with the sound of a cricket. This is the only toad species native to our region that lays its eggs singly. Tadpoles metamorphose in 6 to 8 weeks. This species is nocturnal through the hot summer months, but may be active in the morning or late afternoon when temperatures are cool enough.

Canyon Treefrog (Hyla arenicolor)

Order: Salientia
Family: Hylidae (treefrogs)
Spanish name: rana

Distinguishing Features

This is a small treefrog with highly variable pattern and color. It grows to 2½ inches (56 mm) with a ground color of cream to brown and irregular bars, blotches, and spots of olive to brown. Its color matches its substrate extremely well. Large adhesive toe pads are present on all 4 feet. Adult males have dusky (darkened) or yellow throats, whereas females have white to cream colored throats (which match the underside).

Range

Barely entering Colorado, this treefrog is mainly found in southern Utah, western New Mexico, southwest Texas, all but western Arizona, and northern Mexico at elevations up to 9800 feet (2990 m).

Habitat

This species is largely restricted to riparian areas in rocky canyons. It is typically found along streams among medium to large boulders from desert to desert grassland and into oak-pine forests. The canyon treefrog can operate at cooler temperatures than many frogs; it avoids cold surface temperatures by retreating underground.

Life History

The canyon treefrog eats insects of various kinds. It breeds in July and August during summer rains as well as in spring. The abrupt, explosive call of males attracts females to breeding sites; males then mount females and spawning may begin. Eggs are laid in a large mass that floats on the surface of the water.

Comments

This is an extremely well camouflaged species that usually does not move until a potential predator is almost on top of it.

Northern Casque-headed Frog (Pternohyla fodiens)

Order: Salientia
Family: Hylidae (treefrogs)
Other common names: lowland burrowing treefrog
Spanish name: rana, sapito

Distinguishing Features

This treefrog reaches 2¼ inches (63 mm) in length and has a tan to light brown dorsum with a dark brown network of blotches and bars and a creamy white underbelly. The toes are slightly webbed and the toe pads are small for a treefrog. The name “casque”, which means helmet-shaped, is given to this frog because the skin of the head is fused to the skull; there is a fold of skin at the back of the head. Males have dark throats and a double vocal sac.

Range

This toad barely enters the United States in south central Arizona but it is common in western Mexico from Sonora to Michoacán. Occurs from sea level to 4900 feet (1490 m).

Habitat

This species inhabits desertscrub to thornscrub. In Sonora this species is more typically found in riparian areas.

Life History

The northern casque-headed frog is insectivorous, terrestrial or fossorial (burrowing), and nocturnal. It breeds from June to September during the summer rainy season. The male’s call is an explosive, hoarse “wauk-wauk-wauk”.

Comments

After burrowing underground, this species sheds several layers of its epidermis that form a virtual “cocoon” around the entire body and probably reduce dehydration in the dry season. In addition, this species uses its head to block the opening to its burrow. This reduces water loss from the frog’s body, and may protect it from some predators.

Leopard Frog (Rana spp.)

Order: Salientia
Family: Ranidae (true frogs)
Spanish name: rana

Distinguishing Features

At least 9 species of leopard frogs and several close relatives are found in the Sonoran Desert region. Differences among species are small and often indistinguishable to the human eye. All species are fairly large with pointed snouts, webbed hind toes, long, powerful hind limbs, and large external eardrums. Colors vary from tan to green or brown with irregular patterns composed of spots, bars, and blotches of darker green, brown or black.

Range

These frogs occur from coast to coast and from Canada through Mexico. They are found throughout the Sonoran Desert along permanent and intermittent streams from near sea level to 7900 feet (2410 m).

Habitat

These frogs inhabit permanent and intermittent streams, irrigation canals, and some ponds.

Life History

Leopard frogs are insectivorous and piscivorous (fish-eating). Highly aquatic, they often jump into water from the streambank to avoid capture. Leopard frogs may breed year-round, and tadpoles may take more than a year to metamorphose. Tadpoles get very large.

Vanishing Frogs

There appears to be a world-wide decline in amphibian populations. In our region, leopard frogs are much scarcer than in years past. A close relative, the Tarahumara frog (Rana tarahumarae), has disappeared from Arizona, the only place in the United States where it occurred. No one knows for sure why amphibian numbers are decreasing, but surely there is more than one cause. Water pollution, acid rain, ozone depletion and excessive ultraviolet radiation, habitat destruction, and introduced species (such a bullfrogs in Arizona) are being examined as potential causes for the crisis. Unfortunately natural populations of amphibians have not been subjects of intensive, long-term study. We therefore rarely know about normal population fluctuations and cannot easily determine if what we are seeing today is an overall trend or just a temporary aberration.