Physical Description - This species ranges in size from 22-41 mm (1-1.5 in). Coloration varies widely and is changable. Color ranges from brown to green, and patterns range from plain to spotted. There is often a bar between the eyes and a light stripe on the upper lip, shoulder and side of body. The ventrum is white with yellow shading on the axilla, groin, thigh and shank. This species can be distinguished from other hylid species in that it lacks the following characteristics: light spot under the eye, dark "X" on dorsum, and yellow or orange spots on the thigh.

Historical versus Current Distribution - Squirrel treefrogs (Hyla squirella) are found along the Atlantic Coastal Plain from Virginia to the Florida Keys, and along the Gulf Coastal Plain from south Florida to eastern Texas (Wright, 1932; Burt, 1938b; Wright and Wright, 1949; Hoffman, 1955; Duellman and Schwartz, 1958; Hendrickson, 1974; Martof, 1975a; Mount, 1975; Gotte and Ernst, 1987; Conant and Collins, 1991; Petzing and Phillips, 1998a; Mitchell and Reay, 1999; Dixon, 2000). They occur on numerous barrier islands off the southeastern Atlantic coast and Florida Gulf Coast (Martof, 1963; Blaney, 1971; Gibbons and Coker, 1978; Braswell, 1988). Squirrel treefrogs have been introduced into the Bahamas (Crombie, 1972).

Historical versus Current Abundance - Squirrel treefrogs are one of the most common species in Florida (Carr, 1940a; Bartlett and Bartlett, 1999a). Deckert (1914, cited in Wright, 1932) noted Squirrel Treefrogs in southeastern Georgia are "…the commonest of the southern tree toads…found everywhere, in corn fields, sugar cane, about wells and under eaves of stable roofs, barns, outhouses, etc." Large populations of Squirrel Treefrogs were observed in the low country of southern Alabama by Mount (1975), the Mississippi Gulf Coast by Smith and List (1955), and in eastern North Carolina by Robertson and Tyson (1950) and Palmer and Whitehead (1961). In Princess Anne County, Virginia, Hoffman (1955) observed numerous treefrogs that "…came to the bright light of our Coleman lantern." Werler and McCallion (1951) did not encounter this species in their surveys of the early 1940s in the same area. Although Squirrel Treefrogs can be locally abundant (J.C.M., personal observations), historical and current estimates of population sizes are lacking.

Breeding - Reproduction is aquatic.

Breeding migrations - Adults migrate from upland sites to breeding pools during rains (Wright, 1932; Wright and Wright, 1949; J.C.M., personal observations).

Breeding habitat - Woodland or pasture wetlands, flooded roadside ditches, stock ponds, or other shallow bodies of water (Wright, 1932; Wright and Wright, 1949; Gosner and Black, 1956; Mount, 1975). Breeding males call while sitting on shorelines, perched on debris or vegetation, hidden in clumps of grass, and while sitting in 1–2 cm of water (Carr, 1940a; Wright and Wright, 1949; Gosner and Black, 1956; Duellman and Schwartz, 1958). Mount (1975) reported that males call from a perch 30–60 cm above the water or from a bank near the water’s edge.

Breeding periods - Seasonal breeding times vary with latitude but usually coincide with spring and summer rains (Wright, 1932; Wright and Wright, 1949). The common name of “rain frog” reflects the tendency for this species to call during the day when rain is approaching, although males produce a raspy, squirrel-like call dissimilar from the breeding call (Wright and Wright, 1949; Duellman and Schwartz, 1958; Mount, 1975; Garrett and Barker, 1987). Squirrel treefrogs breed from mid April to mid August in Alabama (Mount, 1975); early April to August in northern Florida (Carr, 1940a; Einem and Ober, 1956); late March to early August in southern Florida (Duellman and Schwartz, 1958); May–August in North Carolina (Brandt, 1936a); and March–October in Texas (Garrett and Barker, 1987). In Florida, “Full choruses come with July electrical storms” (Carr, 1940a).

Diel activity and breeding cycles have been understudied. Squirrel treefrogs are nocturnal and seldom seen abroad during the day. Buchanan (1992) observed treefrogs in Louisiana leave and re-enter diurnal retreats at dusk and dawn, respectively, and experience peak periods of activity at 2000–2300 and 0300–0500 h.

Egg deposition sites - Wright (1932) stated that eggs are laid in shallow pools and that "no end of tadpoles must be lost from drying of breeding places," indicating the ephemeral nature of the larval habitat. Eggs may be deposited singly or in clusters on the bottom or attached to vegetation (Wright, 1932; Wright and Wright, 1949; Livezey and Wright, 1947; Brugger, 1984; Bartlett and Bartlett, 1999a). Orton (1947) noted that eggs "were scattered singly or in pairs on debris in water about 3–6 inches [7.5–15 cm] deep."

Altig & McDiarmid 2015 - Classification and Description:

Clutch size - Females lay > 950 eggs (Livezey and Wright, 1947). Wright (1932) cited egg counts of 942 and 972, and Martof et al. (1980) noted 1,000 eggs/clutch. Clutch size from five females in northern Florida averaged 1,059 (Brugger, 1984). Production of > 1 clutch/year has not been reported.

Length of larval stage - Time from deposition to hatching is 24–43 hr following ovulation (Wright, 1932; Beck, 1997). Tadpoles metamorphose after 40–50 d (Wright and Wright, 1949; Garrett and Barker, 1987) at 11–13 mm (Wright, 1932; Martof et al., 1980). Beck (1997) reported experimental larval periods of 54–77 d at 22 ˚C with low to constant feeding rates and body mass at metamorphosis from 0.25–0.52 g.

Larvae Food - Tadpoles are suspension feeders that eat organic and inorganic food particles they scrape from rock, plant, and log substrates.

Cover - Tadpoles use high habitat complexity to escape predation by dragonfly naiads (Anax junius) and giant water bugs (Lethocerus americanus; Babbitt and Tanner, 1997). Some ephemeral pools, however, lack cover (J.C.M., personal observation), and tadpoles probably experience variable rates of mortality.

Larval polymorphisms - Not known to occur.

Features of metamorphosis - Metamorphosis appears to occur over extended periods. Wright (1932) reported a 2-wk duration.

Post-metamorphic migrations - Recently metamorphosed animals emerge from breeding pools and migrate to upland feeding sites and shelters. Goin and Goin (1957) observed numerous squirrel treefrog juveniles entering their yard in northern Florida from October–December, but none of the migrations were en masse. Pool emergence and post-metamorphic migrations have not been quantified.

Juvenile Habitat - Juveniles occupy habitats similar to adults, although Neill (1951a) noted that many Squirrel Treefrogs found in bromeliad plants are recently metamorphosed animals. Goin and Goin (1957) found that newly arriving juveniles initially used palmettos for cover, but subsequently moved to more permanent shelters including oaks, holly trees, and magnolias. They noted that suitability of holly leaves as overwintering sites reflects the structure of the leaves, as they are leathery and tend to curl toward the underside. Juvenile Squirrel Treefrogs frequently select a position between two leaves that lie one over the other. Juveniles also remained under inverted tin cans atop stakes in their yard during the winter. Site shifts occurred from natural to unnatural cover from autumn to spring.

Adult Habitat - Squirrel treefrogs show little discrimination in their selection of major habitat types (Carr, 1940a). They occur in and around buildings, in gardens, grasslands, weed or brush tangles, bottomland hardwoods, riparian zones, open woodlands, pinelands, trees, vines, cypress stands, longleaf pine/turkey oak/wiregrass associations, and longleaf pine/slash pine flatwoods—in almost any place associated with moisture, food, and cover (Wright, 1932; Carr, 1940a; Wright and Wright, 1949; Anderson et al., 1952; Funderburg, 1955; Goin and Goin, 1957; Goin, 1958; Duellman and Schwartz, 1958; McComb and Noble, 1981; Enge and Marion, 1986; Garrett and Barker, 1987; Conant and Collins, 1991; Dodd, 1992; Lamb et al., 1998). Squirrel treefrogs exhibit some preference for open woodlands, such as mature pine and mixed hammock forests and open woody areas (Wright, 1932; Carr, 1940a; Wright and Wright, 1949; Delzell, 1979). They occur in trash piles (Ashton and Ashton, 1988) and bromeliad plants (Neill, 1951a), and often select narrow spaces in human structures (Goin and Goin, 1957). Squirrel treefrogs are known for their ability to change colors to match their backgrounds (Wright, 1932; Wright and Wright, 1949).

Populations of Squirrel Treefrogs occupy coastal estuarine and harsh barrier island habitats. Engles (1952) found them on, in, and under logs surrounded by meters of bare, dry sand in the wrack zone, and in all vegetated habitats on the Outer Banks of North Carolina. Neill (1958a) noted that this treefrog breeds in rainwater pools affected by saltwater spray in the Florida Keys. Webb (1965) determined that the salinity of a pool with Squirrel Treefrog tadpoles on Bogue Bank (a barrier island off North Carolina) was 47% of full-strength sea water.

Home Range Size - Home ranges have not been reported, but Neill (1957b) noted that squirrel treefrogs apparently establish temporary home ranges, which they occupy for days to weeks. Adults in northern Florida returned to the same resting places day after day, even after retreating to other sites during inclement weather (Goin and Goin, 1957).

Territories - Analyses of territorial behavior have not been published.

Aestivation/Avoiding Dessication - Squirrel treefrogs will often aestivate communally. Carr (1940a) wrote, "Several are found in the same hollow tree or in the axils of the same royal or coco-palm petiole when numerous available and apparently identical retreats are unoccupied." Of the eight species of hylid frogs studied by Farrell and MacMahon (1969), Squirrel Treefrogs had the lowest water content, and females were composed of less water than males. Squirrel treefrogs will tolerate an average of 34% of total weight loss in desiccating conditions before succumbing—about average for the species studied by Farrell and MacMahon (1969).

Seasonal Migrations - Migrations are tied to breeding and metamorphic events; most are apparently tied to periods of rain.

Torpor (Hibernation) - Carr (1940a) writes: "They are gregarious hibernators, thirty or forty sometimes congregating under a loose slab of bark." Squirrel treefrogs hibernate beneath bark of pine stumps and logs and decaying bark of trees (Allen, 1932; Neill, 1948b). Adults may be seen on warm days in northern Florida during the winter; the lowest air temperature at which a juvenile Squirrel Treefrog was active measured 6.7 ˚C (Goin and Goin, 1957; Goin, 1958). They also noted that upon the approach of a cold front, frogs sought more secure shelters, such as under leaf mold and rotten bark.

Interspecific Associations/Exclusions - Wright and Wright (1949) noted that Squirrel Treefrogs breed in association with Eastern Spadefoots (Scaphiopus holbrookii) and Gopher Frogs (Lithobates capito). In New Orleans, Squirrel Treefrogs called with Gulf Coast Toads (Anaxyrus nebulifer), Fowler's toads (Anaxyrus fowleri), and Eastern Narrow-mouth Toads (Gastrophryne carolinensis; Volpe, 1956). One of us (J.C.M.) observed breeding in a shallow wetland in eastern North Carolina along with Southern Toads (Anaxyrus terrestris), Barking Treefrogs (Hyla gratiosa), Eastern Spadefoots, and Coastal Plains Leopard Frog (Lithobates sphenocephalus utricularius), and in Virginia with Fowler's toads, Cope's gray treefrogs (Hyla chrysoscelis), Green Treefrogs (Hyla cinerea), Eastern Narrow-mouthed Toads, and Eastern Spadefoots.

Goin and Goin (1953) and Goin (1958) noted that where Squirrel Treefrogs co-occur with Green Treefrogs (Hyla cinerea) in Alachua County, Florida, the latter prefer low shrubbery and more permanent breeding sites and the former prefer the canopy and ephemeral breeding sites. Squirrel Treefrogs were found trapped in a ditch dug to accommodate a pipeline along with seven species of salamanders, eight other species of hylids, five species of ranids, five species of bufonids, and Eastern Narrow-mouthed Toads (Gastrophryne carolinensis; Anderson et al., 1952). Volpe (1956) found amplexed pairs of Squirrel Treefrogs and Eastern Narrow-mouthed Toads (two pairs of male Squirrel Treefrogs with female Eastern Narrow-mouthed Toads, three pairs of male Eastern Narrow-mouthed Toads with female Squirrel Treefrogs). None of the pairs produced viable eggs; the sperm did not penetrate the eggs.

Age/Size at Reproductive Maturity - Wright (1932) noted 13 mm body length as size at metamorphosis and estimated that juveniles grow to 19–23 mm during their first year and that 2-yr-olds were > 26 mm in size. Adult body length is 22–41 mm (Wright and Wright, 1949; Martof, 1975a; Martof et al., 1980; Conant and Collins, 1991) and maximum size will reach 45 mm (Mount, 1975). Males and females are similar in size (Wright and Wright, 1949; Duellman and Schwartz, 1958).

Longevity - A wild-caught adult lived 8.5 yr in captivity (Snider and Bowler, 1992).

Feeding Behavior - Squirrel Treefrogs are aggressive predators that feed on insects and other invertebrates (Wright, 1932; Garrett and Barker, 1987). Carr (1940a) noted that they are "Often present in enormous numbers along lake-shores when chironomids (Diptera) are emerging; they also collect around lamp posts and lighted windows at night. I once saw nine young in a circle around a pile of newly deposited cow-dung, awaiting and devouring the midges attracted thereto." Duellman and Schwartz (1958) examined the stomachs of 20 individuals and found that 9 were empty, 2 contained only plant debris, and 4 contained beetles (Coleoptera); other stomachs contained crustacean (crayfish?) remains, a spider (Arachnida), a cricket (Orthoptera), and an ant (Hymenoptera). Brugger (1984) found that two groups of arthropods (Arachnida, Isoptera) and three orders of insects (Coleoptera, Orthoptera, Hymenoptera) dominated the diet of frogs from northern Florida. Goin and Goin (1957) noted that differences in habitats selected by adults and juveniles may result in dietary differences.

Predators - Duellman and Schwartz (1958) observed ribbon snakes (Thamnophis sauritus) feeding on Squirrel Treefrogs. Other predators undoubtedly include small mammals, birds, other frogs, other snakes, and aquatic invertebrates. Dragonfly naiads and water bugs (Lethocerus) eat tadpoles (Babbitt and Tanner, 1997).

Anti-Predator Mechanisms - Their small size, propensity for seeking small hiding places, and ability to change colors to match their background probably aid in avoiding visual predators.

Diseases - None reported.

Parasites - None described.

Conservation - Pague and Mitchell (1987) noted that some populations in urbanized areas of southeastern Virginia had become extirpated. However, Neill (1950a) and Delis et al. (1996) found Squirrel Treefrogs relatively abundant in urban areas of Augusta, Georgia, and Tampa, Florida, respectively. Although Squirrel Treefrogs are well known to cross roads at night in rains (e.g., Mount, 1975), the effect of road mortality on size and structure of urban populations is unknown.

• Altig, Ronald & McDiarmid, Roy W. 2015. Handbook of Larval Amphibians of the United States and Canada. Cornell University Press, Ithaca, NY. 341 pages.
• AmphibiaWeb. 2020. University of California, Berkeley, CA, USA.
• Conant, Roger and, Collins, John T., 2016, Peterson Field Guide: Reptiles and Amphibians, Eastern and Central North America, 494 pgs., Houghton Mifflin Company., New York
• Duellman, William E. and, Trueb, Linda, 1986, Biology of Amphibians, 671 pgs., The Johns Hopkins University Press, Baltimore
• Martof, B.S., Palmer, W.M., Bailey, J.R., Harrison, III J.R., 1980, Amphibians and Reptiles of the Carolinas and Virginia, 264 pgs., UNC Press, Chapel Hill, NC
• Wilson, L.A., 1995, Land manager's guide to the amphibians and reptiles of the South, 360 pp. pgs., The Nature Conservancy, Southeastern Region, Chapel Hill, NC