Amphibians of North Carolina
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NC Records

Lithobates virgatipes - Carpenter Frog


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Taxonomy
Class: Amphibia Order: Anura Family: Ranidae Synonym: Rana virgatipes
Taxonomic Comments: Frost et al. (2006) placed species in North American that were formerly in the very large genus Rana into a separate genus, Lithobates, to distinguish them from a large and predominantly Eurasian genus Rana (sensu stricto). There have been numerous arguments put forth for well over a decade about whether these species should be placed back into Rana or retained as Lithobates, with some supporting placing Lithobates as a subgroup within Rana and others supporting the recognition of both genera. There has been no clear resolution of the issue, and both Lithobates and Rana continue to be widely used in recent published literature on North American species. Here, we follow the recommendations of the Society for the Study of Amphibians and Reptiles' Standard English Names Committee and use Lithobates for North American representatives of this group.
Species Comments: As Dodd (2013) noted, much of our understanding of the life history and ecology of this species is based on studies of northern populations. Detailed life history studies of southern populations are needed.
Identification
Description: The adults are medium-sized frogs and one of the smaller ranids in eastern North America. The dorsal ground color is rather drab and can be olive green, tan, or various shades of medium to dark brown. The ground is usually overlain with small blackish spots or flecks, and a series of raised, scattered tubercles are present on the skin. The most conspicuous features are two yellowish, reddish-brown, or light brown lines that extend along each side of the body. The first is a dorsolateral line that extends from behind the eye towards the upper insertion of the rear limbs. It is brightest on the anterior half and fades out posteriorly. The second line runs from the snout backwards along the upper jaw, then below the tympanum and along the lower side of the body towards the groin. It tends to be broader along the body and often fades posteriorly. Blackish-brown spots, blotches, or mottling are present along the lower side of the body that are more prominent than the dorsal markings, and the belly is whitish to yellowish white with darker spots (Dodd 2013). The rear of the femur has alternating light and dark bars, and the underside of the rear leg has blackish-brown wormy or variegated markings that extend onto the belly. The degree of development of these can vary markedly among individuals (e.g., Fowler 1905). This species lacks a dorsolateral fold, but does have a supra-tympanic fold that extends from the back of the eye around the dorsal and posterior margin of the tympanum. The longest toes of the rear feet extend well beyond the webbing, which is helpful for distinguishing this species from young of the Pig Frog (Beane et al. 2010, Dodd 2013, Jensen et al. 2008).

Sexually active males have a swollen thumb, two lateral vocal sacs, and a tympanum that is slightly larger than that of females of comparable size. Adult males in local populations tend to average only slightly smaller than adult females (Dodd 2013). Adult males at a site in southern New Jersey ranged from 39-62 mm SUL (Given 1988a). Wright and Wright (1949) reported a range of 41-63 mm SUL for males and 41–66 mm SUL for females, but the largest reported male is 68 mm SUL versus 73 mm SUL for a female (Dodd 2013).

The older tadpoles vary from grayish or brown above with black spots or blotches. The tail musculature has a dark stripe and there is a distinctive stripe or row of dark dots along the center of the dorsal tail fin (Dodd 2013, Jensen et al. 2008). The edges of the dorsal and ventral fins have a narrow zone of broken dark blotches along their length.
Vocalizations: The males produce several types of vocalizations that include the advertisement call, single-note and multi-note aggressive calls, a growl that is given when fighting, and a release call. The most familiar is the distinctive “clack-it” or “pu-tunk” advertisement call. This is usually given several times in succession (range = 1-10 calls in succession) and sounds like a team of carpenters hammering away on a roof. Given the otherwise secretive nature of this species, these calls are usually the easiest way to detect the presence of this species.

The singing behavior of Carpenter Frogs has been well-studied by Given (1987, 1988b). The males are territorial and occupy small areas that are used for mating. The double-note calls given by the males are used to advertise their presence both to females and to other males, and the characteristics of the calls provide information on the size of the singer. Larger males have calls with lower dominant frequencies – deeper voices. This can be seen in the spectrograph below as areas of brighter and wider areas of red along the vertical bars representing the individual notes. The differences between males can also be easily heard, with several examples of smaller males and a few larger males included within this sound clip. Females use this information to help select the fittest males to mate with. Males use this same information to determine the probable physical strength of neighboring males. Given (1987, 1988b) found that playbacks of large males would cause smaller males to move away, while playbacks of small males to large males would cause the large males to approach the speaker. In addition to the advertisement calls, the males also produce other types of calls used in agonistic encounters. Females are also capable of producing short calls. Choruses typically occur throughout the night, but they also occur much more sporadically -- as in the example shown here -- during late afternoon.
Technical Reference: Dodd (2013)
Online Photos:    Google   iNaturalist
Observation Methods: Carpenter Frogs are difficult to find by direct searches and are most easily documented by listening for the distinctive advertisement calls during the spring and summer months. Calling mostly occurs from dusk through dawn, but can occasionally be heard during the day, particularly during cloudy or rainy weather.

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AmphibiaWeb Account
Distribution in North Carolina
Distribution Comments: The Carpenter Frog occurs along the Atlantic Coastal Plain from the southern half of New Jersey to extreme northern Florida. This species is mostly found along the lower Coastal Plain, but extends as far inland as the Fall Line in South Carolina and adjacent areas in southeastern North Carolina. Populations in North Carolina are most common in the lower Coastal Plain and the Sandhills and vicinity.
Distribution Reference: Beane et al. (2010), Dodd (2013)
County Map: Clicking on a county returns the records for the species in that county.
GBIF Global Distribution
Key Habitat Requirements
Habitat: This is a mostly aquatic species that lives in or around the margins of coastal wetlands. The adults and juveniles are often found in acidic, brown water or blackwater wetlands such as pocosins, sphagnum bogs, the sluggish sections of blackwater creeks and rivers, and bottomland swamp-forest complexes. However, many other habitats are used. The larvae sometimes overwinter before metamorphosing, so most sites that support populations are semipermanent or permanent -- with the latter being preferred. Populations are commonly found in acidic wetlands where there are extensive sphagnum moss mats. Sites that are forested or have nearby forest are also more likely to support local populations (Otto et al. 2007, Simpson et al. 2021).

Natural habitats that are used throughout the range include cranberry bogs, pocosins, lakes, Carolina Bays, Delmarva Bays, seasonally flooded woodland pools, beaver ponds, bottomland swamps, freshwater marshes, interdunal cypress swales, oxbow lakes, and the sluggish sections of creeks and rivers and their associated swamplands. In addition to frequenting bottomland sites, Russell et al. (2002a) reported that populations in South Carolina use small wetlands that are interspersed within Longleaf Pine forests on sandhill ridges (Russell et al. 2002a). Artificial wetlands are also occasionally used such as impoundments, borrow pits, drainage ditches, canals, and constructed ponds. Artificial sites that have lots of floating or emergent vegetation and nearby forest cover that keep the sites acidified are preferred (Dodd 2013, Otto et al. 2007, Smalling et al. 2021).

Populations in North Carolina have been found in pocosins, Carolina Bays, peaty bogs, semipermanent wetlands in Longleaf Pine forests, borrow pit ponds, drainage ditches, the sluggish sections of streams and rivers, and in swamps and oxbow ponds.
Environmental and Physiological Tolerances: Lithobates virgatipes is an acid-tolerant species, with the lethal and critical pH values for this species around 3.5 and 3.6–3.8 (Dodd 2013, Gosner and Black 1957a). The eggs and larvae can survive in wetlands in the New Jersey Pine Barrens that have a pH of 3.8–4.1 (Bunnell and Zampella 1999).
Biotic Relationships: Very little is known about the defenses that the larvae have against aquatic predators. It is uncertain to what extent they are palatable or have behavioral avoidance mechanisms. They frequently coexist with predatory fishes, which suggests that they may be unpalatable. The predators of the juveniles and adults are poorly documented. They include the Banded Watersnake (Nerodia fasciata), the Common Watersnake (Nerodia sipedon) and Eastern Racer (Coluber constrictor). Birds and mammals that forage along shorelines undoubtedly take them (AmphibiaWeb 2022, Dodd 2013).
See also Habitat Account for Coastal Plain Blackwater Wetlands
Life History and Autecology
Breeding and Courtship: The Carpenter Frog has a prolonged breeding season, with the males calling from mid-March through September depending on the location and local climatic conditions (Dodd 2013). Calling occurs from late April to early August in New Jersey (Fowler 1905, Conant 1947; Given 1987, 1988a, 1988b, 1990), and from March to September in Virginia, with a peak from April to August (Georgel 2001). Gaul and Mitchell (2007) documented calling from mid-March to early August in North Carolina, while Jensen et al. (2008) reported calling from early March through the end of August in Georgia. Given (1988b) found amplexed pairs throughout most of the calling season.

Standaert (1967) found that males tend to outnumber females at the breeding sites, particularly from April through June. Most of our knowledge about the breeding biology of this species is based on detailed studies by Given (1987, 1988a, 1988b) in southern New Jersey. The males at his study site set up very small territories near the shore of a lake. Individual territories had a median radius of only 1 meter (range = 0.5-6.5 m) and were often close to other calling males. Around 24% of the individuals remained in their territory throughout the breeding season, while 34% switched to new territories, often after engaging in a territorial dispute. The remainder either disappeared or wandered to the end of the breeding season. Individuals that left territories moved an average of 22.5 m. Calling and territorial defense was energetically expensive, with territory holders loosing weight and fat reserves during the breeding season (Given 1988a).

Aggressive encounters between rival males involve either active calling or physical fights. During aggressive calling, rival males produce alternating single notes at a relatively high rate that sound like explosive pops (Given 1987). Males are able to judge the size of rivals based on their vocal characteristics (Given 1987). Aggressive calling can escalate into a fight that is preceded by a male emitting a multi-note aggressive call. Fighting involves brief wrestling matches in which the males lock forearms and attempt to mount opponents. These sometimes occurred several times over the course of a night and for several nights, but usually only for a single night.

Neighboring males rarely fight each other, and most fights occur with unknown strangers that enter a male's territory. The residents usually win these encounters, and larger males almost always win when fighting smaller males. In Given's studies, satellite males were present in some territories. These maintained low postures and were generally smaller than territory holders. They were typically either young males or males that had lost territorial disputes.

Females appear to choose their mates based on the characteristics of the male's call and pick relatively large males. Males that call for a relatively long number of nights also have more matings. Egg laying and fertilization has not been described in detail, but females presumably begin laying eggs within a few hours after being amplexed. They often lay their eggs outside of the male's territory.
Reproductive Mode: Each female produces a single globular to somewhat elongated egg mass that is attached to plant stems or other vegetation or debris. The egg masses are placed from 0.05–1.0 m below the water surface (Dodd 2013, Given 1990, Wright 1932) and vary from around 6.5 × 6.5 cm to 5 × 10 cm in width and length. Wright (1932) noted that they closely resemble those of the southern Leopard Frog, but lack the inner membrane and often have a bluish tinge. The freshly laid eggs are black above, creamy white below, and have a single jelly envelop. Specimens examined by Wright (1932) had eggs that averaged 1.6 mm (range = 1.5-1.8 mm) and jelly envelopes that averaged 5.4 mm (range = 3.8-6.9 mm).

Estimates of clutch sizes are largely lacking. Wright (1932) gave counts of 349 and 474 from two masses, and Wright and Wright (1949) reported that the egg masses have 200–600 eggs (from Wright 1932).
Aquatic Life History: Very little is known about the larval ecology of L. virgatipes. The hatchlings grow rapidly and can reach 90-100 mm TL before transforming (Jensen et al. 2008, Wright 1932). The length of the larval period varies depending on the seasonal time of breeding and whether the tadpoles overwinter. Standaert (1967) found that larvae in New Jersey first appeared in late May and metamorphosed 4-5 months later, with a peak in September. There was no evidence of overwintering larvae. In contrast, Wright (1932) found metamorphosing tadpoles in New Jersey at the end of May that presumably overwintered. The young metamorphs vary from 23-36 mm SUL. Wright (1932) reported size ranges of 23–31 mm SUL for New Jersey specimens, along with two from Georgia that were 27 and 29 mm SUL. Standaert (1967) reported that the mean size in New Jersey was 32 mm SUL (range = 28-36 mm).
Terrestrial Life History: Dodd (2013) noted that individuals that metamorphose in summer may reach the minimum size of sexual maturity before overwintering, then breed the following spring. In cases where females oviposit during the latter part of the breeding season and the tadpoles overwinter, sexual maturity may not be reached until the following summer, approximately 10–12 months after egg deposition.

The young metamorphs are capable of rapid growth. Standaert (1967; summarized by Dodd 2013) found that individuals in New Jersey that metamorphose in the summer commonly reach 34–36 mm SUL before overwintering, with a few frogs growing to as large as 49 mm SUL and becoming sexually mature by October. After overwintering, most juveniles resume growing and become sexually mature by mid-June. Most males become sexually mature at 40–45 mm SUL in Virginia (Georgel 2001) and 42–44 mm SUL in New Jersey (Dodd 2013, Standaert 1967).

The juveniles and adults are active except during the coldest winter months. They can commonly be found in or along the margins of wetlands. At sites where extensive submerged sphagnum mats are present, Carpenter Frogs often sit partially submerged in the water while resting on the moss. The adults are wary and will swim short distances and seek shelter in submerged vegetation if approached (Dodd 2013, Fowler 1905). At sites without sphagnum mats, individuals often rest in vegetated shallows or among floating vegetation such as lily pad beds (Given 1988a, Wright 1932). Standaert (1967) noted that the males call from shallow water near the shoreline, then move to more open water following breeding. Overwintering occurs in the same aquatic habitats that are used during the warmer months of the year (Dodd 2013).

Like other ranids in the eastern US, the juveniles and adults appear to be gape-limited, generalist predators that consume a wide range of prey. Insects are the dietary mainstay, although there are two recorded instances of individuals cannibalizing a tadpole and taking a larval Lesser Siren (Dodd 2013, Georgel 2001). Invertebrate prey in Virginia specimens included beetles, collembolans, flies, ants, dragonflies, leafhoppers, true bugs, and homopterans (Georgel 2001).

Given (1988a) found that only 3 of the 26 males that he monitored at a lake site in New Jersey were present the following year, which suggests high annual mortality rates at this site. Standaert (1967) found dead frogs in shallow pools in spring that probably died from winterkill.
General Ecology
Population Ecology: Information on local population sizes and population organization is largely lacking. The extent to which the young metamorphs or adults move between sites is poorly documented, but the movement of adults appears to be very limited. Standaert (1967) noted that small frogs dispersed from a large natal pond to a nearby smaller pond in fall then returned the following summer as the pond dried. Smalling et al. (2021) found them in constructed ponds in New Jersey, which suggests that the juveniles may move substantial distances from their natal ponds.
Community Ecology: Larvae of the Carpenter Frog use breeding sites that support numerous predators and potential competitors, but interactions between these species are poorly documented. Many of the natural habitats that are used are highly acidic, which likely serves to eliminate many acid-intolerant anurans that are potential competitors or predators, such as the American Bullfrog (Bunnell and Zampella, 1999, Gosner and Black 1957a, Zampella and Bunnell 2000, Simpson et al. 2021).

Given (1990) examined interactions between territorial males of L. clamitans and L. virgatipes and did not find strong evidence of one species excluding the other from breeding microhabitats. He observed only two instances in which L. clamitans attacked an intruding L. virgatipes.
Adverse Environmental Impacts
Habitat Loss: Lithobates virgatipes has a discontinuous range on the Atlantic Coastal Plain and some populations have been lost due to wetland filling and deforestation (Dodd 2013). Otto et al. (2007) and Simpson et al. (2021) found that populations are often found at sites that are forested or have forests within 50 m or so of the breeding sites. This may reflect an indirect effect related to the fact that depressional wetlands are naturally acidic, and that watershed development and loss of forest cover can lead to markedly higher water pH. This in turn may allow the replacement of narrowly distributed, acid-tolerant species by more widespread species that are not tolerant of acidic waters.
Status in North Carolina
NHP State Rank: S4
Global Rank: G4
Populations: The Carpenter Frog can be common in some areas such as the New Jersey Pine Barrens, but many local populations in North Carolina and Virginia tend to be small (AmphibiaWeb 2022).
Status Comments: The status of populations in North Carolina has been difficult to determine due to issues with accurately monitoring populations. Resurveys of known historical populations in Maryland, New Jersey, Virginia and Florida provide evidence of declines (Brady 1927, Dodd 2013, Given 1999a, Krysko et al. (2019).
Stewardship: Local populations are best maintained by protecting natural breeding sites and having a forested buffer of 50 m or more around the sites.

Photo Gallery for Lithobates virgatipes - Carpenter Frog

4 photos are shown.

Recorded by: Yasuhiko Komatsu
Dare Co.
Comment: Creative Commons from iNaturalist (CC BY-NC 4.0 DEED; original cropped).		Recorded by: Travis McLain
Dare Co.
Recorded by: Mark Shields
Onslow Co.		Recorded by: E. Corey
Bladen Co.