By Chris Montross – Darkhorse Herpetoculture
A true gem of the Southeast is found hiding deep in the biting fly and mosquito ridden mangrove forests of the coastal waters of south Florida.
The Mangrove Saltmarsh Snake (Nerodia clarkii compressicauda) is an extremely polymorphic subspecies of the Saltmarsh Snake (N.clarkii) that occurs in some of the environmentally harshest habitat where their activities mostly occurs after the sun sets along the coast. Nerodia clarkii was originally described as a species in 1853 by Baird and Girard. Then taxonomically the Mangrove Saltmarsh has bounced around but have been kept as one of three subspecies of Nerodia clarkii since the 1980s. There were as a many as five subspecies of Tropidonotus compressicauda recognized by E.D Cope around the turn of the 1900s. The subspecies compressicauda, walker, taeniata, obscura and compsolaerna once helped describe the various phenotypes originally encountered along the coastal waters of southern Florida.
As a species, N.clarkii range from Volusia Co, FL south around the coastline of Florida and west along the gulf coast to Neuces Co, TX. There is only an approximate 80 mile section of the Florida panhandle where habitat seems to lack that they cannot be found. Mangrove Saltmarshes occur in the Red Mangrove (Rhizophora mangle) dominated swamps and coast line from Indian River Co, FL south through the Keys to northern Cuba and then north to southern Levy Co, FL where the habitat changes to predominantly coastal marsh grasses and descreasingly less mangrove trees. There is a close relationship between N.clarkii and N. fasciata ssp across the range. Where freshwater and saltwater meet hybrids or integrades can be found. Man made canals have also added to the gene mixing by unnaturally bringing water channels and corridors of travel to areas where they never previously existed.
A relatively small species compared to others in the genus, the Mangroves rarely reach 30” for large females while most stay much smaller. Adult males generally do not get larger than 12” and specimens from the Florida Keys that are isolated from Florida Banded Watersnake (N. fasciata pictiventris) populations tend to be even smaller. Due to the high variability of color and patterns seen across the range, the linear ventral pattern is the tell-tale identification for all three subspecies. Any deviation from this pattern is considered to have N. fasciata influence. Although the red (yellow/orange) phase specimens frequently have little to no ventral markings making that key a challenge with some specimens. But even with them, there is a light coloration central along the ventral length that can be distinguished. I have observed Nerodia specimens many miles inland with evidence ventrally of gene influence with N.clarkii.
Despite their habitat adapted preference, they do not ingest or are they able to process saltwater. Water is absorbed through food intake or during rainstorms where freshwater will sit on top of the denser
saltwater initially. Mullins,1992 found they seem to be better suited as ambush or very slow movement hunters over a more active hunting style. I have had similar experiences with captive specimens over the years. They take very quickly to being fed by long tweezers as opposed to finding food left for them as seen in other Nerodia species. A quick tap to the side of the head or neck invokes a quick sweeping strike for food.
I took the plunge in May of 2017 and acquired 2.2 freshly caught adult Mangroves from Estero Bay in Lee Co, FL. As hoped, the females were both gravid and the resulting f1 offspring added additional genetic stock not related to the males (most likely). Those two red type females dropped 8 and 9 beautiful offspring that summer. One of the litters was all red phenotype, while the other was mixed in colors and patterns. Late the following year I added a group of short term captives from the same area via a friend doing studies with the species and didn’t want to release them after having had them in captivity for that short time.
On average, I have found wild caught Mangroves to be quite challenging to acclimate to captivity over Banded Waters. Many are very picky and my reluctance (I am better about it now) to offer live food for any length of time to due to parasite transfer, added to the failure to acclimation early on. I was able to breed some of the second batch of acquisitions to add new genetics to my captive colony. They are very sensitive, like other Nerodia, to captive enviroments that are wet, humid, have stagnant air, not cleaned often enough, have fouled water (which they use routinely as a toilet) and will perish if not kept to their liking. “Blister” disease, an acute bacterial infection brought on by stress associated with the listed conditions is often the culprit of their demise. Though starvation and likely parasite load compromise add to the headache of establishing wild caught specimens as well as long term maintenance of the them. Captive born offspring don’t seem to have much of the challenges seen with keeping wild caught Mangroves but the captive conditions must be kept dry with low humidity to ensure happy animals and long term success.
Through trial and error, more than anything, I have found a well ventilated enclosure with a dry substrate and water bowl big enough to soak in to be ideal. I have been using Sterlite brand tubs of varying sizes with countless ventilation holes added to the sides and lid to be a successful combination. I use 66 quart bins for adult pairs or small groups of subadults and both 7 and 15 quart tubs for neonate groups of varying numbers. Kiln dried pine shavings are used as a substrate that I acquire from my local feed store. I have found this to be an ideal substrate that is readily available, affordable and effective. I also use this with all of my other colubrids. Multiple hides in the form of paper towel rolls, plastic containers of varying sizes(with small entry holes cut into them) and props to allow them to utilize elevated areas of the enclosures. Of late, I like to use coated metal wire fencing to make perching structures. The elevated wire platforms are easier to clean and disinfect than the limbs I had previously used. These tubs are set on shelving units to allow for airflow all around them. Closed rack systems are not ideal for Nerodia. Air movement is important! A fan will keep the room they are housed in less stagnant. Ambient room temps are maintained between about 77-82 F. A short winter cooling is not necessary but doable into the 50- 60s F. Since they are found in the southern half of the Florida peninsula, other cues such as changes in photoperiod, humid and food availability will trigger ovulation and breeding behavior as well.
Once feeding, whether it be an acclimating wild caught specimen or a captive bred and born neonate, I switch them over to a predominantly rodent diet. Using hairless rodents is important. Although most Nerodia wont even put their mouth on a furred rodent, hair impaction is a concern for a species not accustomed to processing it and hair impaction deaths are known in Thamnophis. Thankfully due to their small size, even the largest females cannot handle much bigger than a small adult mouse and overall they prefer to be offered numerous smaller food items over a single larger one.
I do offer fish periodically, more often when young. Baby Mangroves are often quite small and it can take many months before they can handle even the freshest of pink mice. Pacific Whiting(Hake), Swai and occasionally Catfish are my usual grabs in the local grocery store freezer. Mosquitofish (Gambusia affinis) are like crack for baby Nerodia in general and I try to take the time to catch some and keep ziplock bags stocked in my freezer for them. The rodents are denser, higher calorie food items than their natural diet. By utilizing rodents heavily, it allows me to not have to feed them any more often than I would for other colubrid species I keep. The rodent diet is especially helpful with breeding animals and maintaining adequate weight in reproducing females. Gravid females are ravenous and a few small hairless mice seem to satiate them and keep them in shape. Also, feeding whole food items(such as rodents) is very important for balanced nutritional intake over store bought filets that are just muscle meat and require additional supplementation if used routinely.
Breeding in the wild can take place somewhat year round due to their subtropical climate range, though most breeding occurs in the spring as night time temperatures increase. Gestation lasts about 4 months which is similar to the average egg production and incubation of other regional snakes. I have one female that has double clutched now two years in a row. Kind of an incredible thing for a live bearing species. Heavy feeding is required for these females to maintain good body condition.
Since populations from the Florida Keys are much smaller on average, likely due to a lack of N.f. pictiventris influence genetically, the offspring are notably smaller and more delicate. Neonates are on average are slow growers similar to their close friend, the Florida Banded Watersnake(N.f.pictiventris). I have found that picitventris are much slower growers than the other two subspecies of Bandeds (fasciata and confluens) and compressicauda follow their lead with growth rate expectations. There are always rule breakers that do not know the standard protocol and will grow much quicker than others. More often than not the fast growers are females (not always) and close attention must be paid to young males to ensure they are getting enough food. This even includes adult males since their mature size is paltry compared to their much larger house mates. Their needs and drive to grow is much less than females since they do not play the same role reproductively that the females do. Most of my adult males might get 2-4 food items a month. While their female counterpart/housemates will eat 2-3 mice every 4-7 days depending on the time of year. Most neonates are much more relaxed around their keepers than other species of Watersnakes. Keeping calm when their enclosure is being maintenance and much quicker to recognize us as the bringers of food.
Adults seem to best be housed in groups of 2-3 depending on sex ratio kept. I generally keep pairs together or occasionally bachelor groups for a period of time. Males can be a bit shy and skiddish when housed with females. The food drive of adult females can be intense. So the males will usually keep their distance and stay hidden in paper towel rolls elevated on enclosure furniture. Nerodia in general can get quite stressy about changes to their housing and even housemates. Change is frequently not good. I have had on multiple occasions where I have separated long term pairs up and had one or both go off
food and pass a few months later. This has been observed with most all Nerodia species in general. So I try to limit changes as much as possible. But to help maintain genetic diversity in my colony I feel the need to pair up certain mates to bring forward new or less represented blood and changes must be made to accomplish that goal. So the chances are taken and close attention is paid to the parties involved. My general rule with Mangroves and other Nerodia species is to set them up and leave them be. Which is a challenge since they are high metabolism animals that require very routine enclosure maintenance.
During the breeding season( spring mostly for me) males will tend to care less about food. While females want all you will offer most of the year. During the times that females are opaque and food is of less a concern(but not zero) it is a good time to get some extra meals in the males when the females are less likely to come steal it. The frantic feeding nature of gravid females will generally have the males staying hidden. Two to three pinkie mice will usually do the trick for the males. Once breeding has occurred females can be palpated for developing young. Initially they are just a series of lumps in the mid to caudal abdomen, but later have a pillowy feel as the sacs around the embryos develop. Thus making individual embryo palpation difficult.
As babies are being born, they will usually shed in the first 15 minutes of breaking out of their sac. Litter sizes of 2-14 is what I have experienced, with 5-9 being the average. I separate neonates as a group into a 7 quart Sterilite tub with damp paper towels on the bottom, a water bowl, a dry hide and a wire perch.
The dampened paper towels are not remoistened, but rather allowed to dry out. Just providing the newly born Mangroves the opportunity to stay hydrated in the first 48 hours of life. After about a week I switch the substrate to pine shavings. Starting the neonates is frequently a game of see what they want. Frozen thawed mosquitofish is usually taken by most and pieces of store bought fish as well. But some are stubborn and make me offer live fish. I hate doing this as I know most live fish are full of parasites, but what is one to do. Once feeding on something, baby Mangroves are quick to associate their keeper with food and tong feeding becomes the easiest protocol for me. Other neonate Nerodia species tend to be very flighty for many months and do not seem to have as trusting a nature as these guys. Too often when babies are being born, my access to good collecting grounds for live mosquitofish becomes limited. Water levels in the summer drop and they tend to be out farther from shore where I cannot easily dip net my quota for the outing.
Depending on the size of the litter I find I have to start separating babies into groups based on their feeding habits after about 3-4 weeks. Some are just naturally more aggressive feeders(females frequently) and the shyer babies need to have less competition during feeding opportunities. From birth to adulthood they go through a noticeable ontogenetic change. More so with the darker phenotypes. I have always referred to the phenotypes as Red or Dark. But that is a simplified take on the situation. Baby Red phase are generally tan to orange toned with some amount of red banding, though some can be patternless. While the Dark phase are black and grey at birth. The colors and patterns coming in as they grow. The Dark phase being the most impressive and striking to me. Background colors of brown, black, green, blue, copper and red have been observed in my offspring.
Patterning of the same palate of colors develop over time and subtle colors on scale tips and pattern edges can make for a striking individual. Red phase individuals can develop black speckling and black patternless ones can have a red wash to their look. Red phase can include bright red, faded red, orange, and yellow with or without patterning. Patterning and colors can vary regionally. The brightest reds I have seen are from the Keys and some of the coolest colors from the central west coast of Florida. Litter phenotype expectations is something of a mystery to me still. I have been working on understanding phenotypic inheritance in them and Banded Waters for many years and Mangroves continue to stump me as to where certain colors and tones come from genetically.
Mangrove Salt Marsh Snakes are an amazing species to keep due to their array of phenotypes and overall smaller size. Although captive bred and born stock is very limited in availability and really the species in general, one can find started stock if the desire is there along with some patience.
For further reading
Mullins, Stephen J. 1992, Predatory success as a function of habitat structural complexity in the Mangrove Saltmarsh Snake, Nerodia clarkii compressicauda
Gibbons and Dorcas,2004, North American Watersnakes A Natural History
Krysko, Enge and Moler, 2019, Amphibians and Reptiles of Florida
