Appearance
Underside of Holbrook's southern dusky salamander.
Holbrook’s southern dusky salamanders are dark, small- to medium- sized salamanders with black or brown skin and light speckles along their body. They have a yellow or orange-red light stripe running from the bottom of their eyes to the top of their jaws. There are two rows of white spots lining their sides that can continue onto the tail and become more noticeable. The upper row of spots may be overlaid with red pigment. Their undersides are dotted with many white speckles, resembling stars on a clear night sky. They have a compressed tail that looks blade-like, tapering to a pointed tip. Holbrook’s southern dusky salamanders also have 14 costal grooves –- these are vertical channels along the torso where blood vessels and nerves sit. Adults average 3-6 inches long. Males generally grow larger than females. Males also have a specialized chemical sensing organ under their chin called the mental gland that sends out pheromones for courtship to reproductive females. Young salamanders, called larvae, are mostly black overall with white circles along their bodies that can extend to the sides of their tails. Holbrook’s southern dusky salamander larvae also have external gills on their heads.
Behavior
This species is in the Plethodontidae family, which may also be referred to as the family of “lungless” salamanders. They do not have lungs and instead breathe through thin, moist skin. This species is semi-aquatic. Larvae have external gills and live fully aquatic lives until their metamorphosis, after which they can live in both aquatic and terrestrial habitats. Adults have been observed burrowing into wet ground, peat, or crayfish burrows for shelter.
The Holbrook’s southern dusky salamander engages in courtship practices common to other Plethodontid salamanders. The mating process, called the ‘tail straddle walk’, happens when a female straddles the tail of a male salamander. The male walks forward while dropping a spermatophore (a capsule containing sperm) to the ground and, with the female following behind, guides his mate over the spermatophore for her to collect it with her cloaca (opening used for excretions and reproduction). Females lay eggs from January through September, and eggs begin hatching in early fall. Egg clusters look like miniature bunches of grapes and generally consist of 9-26 eggs. Eggs are laid on land near water sources, usually in nests made from debris placed within small, protected cavities. Females exhibit brooding behavior by staying with their eggs until they hatch. Aquatic larvae metamorphose in the winter and spring following hatching.
A regular diet for these salamanders consists of both aquatic and terrestrial invertebrates like aquatic beetle larvae, spiders, other types of invertebrate larvae, and small adult insects. Cannibalism is common among this species.
Holbrook’s southern dusky salamanders do not hibernate, but they become less active during the colder months. This happens especially in their northern range and in habitats subject to more extreme temperature fluctuation. This often leads to individuals looking for places of consistent temperature that radiates from seeping groundwater.
Habitat
Several species of dusky salamanders can be found throughout the Coastal Plains of North America. Southern dusky salamanders were previously thought to range from Virginia through eastern Louisiana. However, recent research found that southern dusky salamanders were actually four similar looking distinct species. The species named Holbrook’s southern dusky salamander can be found in Alabama, Florida, and Georgia.
Florida is the most southern extent of their range, where they are found eastward of the Escambia River all the way to Citrus, Sumter and Lake counties. They are found in acidic swamp lands or near slow-flowing to almost stagnant streams and ravines where organic debris collects. Other habitats include shallow pools in bottomland forests and flood plains. They may also be observed near shallow blackwater to lay eggs –- such as the edge of a small pond.
Threats
Photo by Peyton Niebanck.
Holbrook’s southern dusky salamanders face a variety of threats, including:
- Habitat loss and alteration: Draining of wetlands as well as siltation, channelization, and pollution of water ways degrade and reduce their habitats.
- Off-road vehicles: The use of off-road vehicles in sensitive wetland habitat can degrade and destroy suitable habitat.
- Environmental changes: Changes in weather and precipitation cause fluctuations in water levels and long-term droughts. These changes may make areas unsuitable for the species to use or allow diseases and pathogens to have increased chances of infecting the species.
- Disease: Amphibians are highly susceptible to diseases due to their extreme sensitivity to slight environmental changes. One hypothesis is that an unknown pathogen, such as chytrid fungus (Batrachochytrium dendrobatidis), may have been responsible for a large-scale population decline throughout the species range in the 1970s. Preliminary disease studies are happening now with museum specimens to investigate this possibility.
- Feral hogs: Wild hogs dig up microhabitats that these salamanders use and can also eat salamanders.
Conservation and Management
Photo by Peyton Neibanck
Since the mid-1970s, there has been a recorded decrease in individuals even from areas without development or with low levels of human disturbance. The cause for this population decline is currently unknown, although scientists are currently studying threats like disease that could be responsible. The U.S. Fish and Wildlife Service was petitioned to list the Holbrook’s southern dusky salamander as Threatened in 2015, and it was found to not warrant federal listing.
The FWC received a request to evaluate the species for state listing in 2022. In December 2023, the FWC Commissioners approved the convening of a Biological Review Group (BRG) to review the species' status against state-listing criteria. The BRG conducted its evaluation of the Holbrook’s southern dusky salamander in 2024 and concluded that it meets the criteria as a State-designated Threatened species due to the restricted area of occupancy and extent of occurrence of the species in Florida. FWC staff will determine a listing recommendation that will be presented to the Commissioners for approval in 2025. Current information on the listing status can be found at MyFWC.com/Listing. The Holbrook’s southern dusky salamander is also already identified as a Species of Greatest Conservation Need in Florida.
How You Can Help
Sharing the value of proper habitat management and the “leave no trace” concept of not littering and throwing away trash in appropriate bins can help maintain salamander habitat.
Disinfecting boots, waders, or other field equipment can help reduce the spread of diseases. More information on disinfecting field equipment.
It is important to keep track of amphibian populations, especially for species that have experienced known declines over the past few decades. To help with this monitoring, you can report sick or dead salamanders and other amphibians by contacting your FWC Regional Office or reporting to the Herpetofaunal Disease Alert System. If you suspect someone is illegally capturing or trafficking wildlife, please contact the FWC Wildlife Alert Hotline: 888-404-3922.