Salamanders in Suburbia: Field Observations from a Drift Fence Study

Over the past 2 years, I have been leading a population study comparing historic and current demography and movement patterns of Jefferson Salamanders (Ambystoma jeffersonianum) and the Unisexual Salamanders that live with them.

Quick sidebar: if you are not already familiar with the Unisexual Salamander Complex, it is a fascinating natural history story that I won’t go into here, but I would encourage readers to investigate (e.g., here and here).

As part of the current population study and its many side projects, we have made several interesting observations that might interest readers of The Drift Fence. I want to share a few of my favourite field observations from the project so far.

Drift Fence Affiliates: Spiders and Eastern Red-backed Salamanders

Over the 2 years of the study, I have noticed large numbers of spiders and Eastern Red-backed Salamanders (Plethodon cinereus) colonizing the drift fence, maybe because the project is in a more urbanized area. Various species of spiders will set up shop along the fabric, behind the stakes, and will use the fence as an attachment point for their webs. We have found female spiders with egg sacs snuggled into the drift fence many times, especially in the warmer months. It makes sense that spiders would like this structure because it likely gives them access to flying insects emerging from the pond and has a lot of surface area that they can use. Terrestrial spiders also get trapped in the pitfalls in decent numbers during warm weather. This was often an unpleasant surprise for project assistants with arachnophobia!

The case of Eastern Red-backed Salamanders as drift fence affiliates is perhaps a little more puzzling. The species naturally occurs at high densities on site, but this year (2025) we discovered large numbers of hatchlings hiding underneath pitfall traps along with gravid females, suggesting that they may be using the structure as a “nursery”. The rapidity with which dozens of red-backed salamanders colonized coverboards at the site also makes me wonder whether the species is somewhat limited by microhabitat structure. We don’t mark Eastern Red-backed Salamanders and so we probably won’t be able to answer this question, but it would be fascinating to know whether the drift fence and pitfall trap setup augments their population by providing additional microhabitat structure.

Fingernail Clams

We couldn’t believe our eyes last year when we found not one, not two, but several clams stuck on the toes of the Jefferson/Unisexual Salamanders we were capturing. At first, we thought it must be an error or perhaps they were parasites. These clams are adapted to live in vernal pools and colonize new sites by “hitching a ride” on amphibians by clamping down onto their toes. Given enough time, they may damage the digit they are attached to, and it is possible they could slow down a salamander that is trying to escape, but mostly they are harmless. Larval Jefferson/Unisexual Salamanders may even feed on them during their development in the pond.

Un-spotted Spotted Salamanders

I knew melanistic or un-spotted Spotted Salamanders (Ambystoma maculatum) existed, but I had never seen one until I started this project. The population of Spotted Salamanders at the suburban site we survey has a relatively large proportion of un-spotted individuals. These salamanders can sometimes look deceptively like the Jefferson/Unisexual Salamanders and have confused some members of our team in the past. The main way to tell the difference is that the Spotted Salamanders are much chunkier, and their head shape is wider and more rounded. But there is a lot of variation, as is often the case.

Cold-tolerant Creatures

When starting this project, I read that Jefferson/Unisexual Salamanders typically migrate to the breeding ponds when temperatures are around 4°C. I quickly learned, however, that this is an ideal, but not necessary for them. I have often found salamanders traveling to the ponds at 1, 2 or 3°C, and on one memorable evening last year, we even found a Jefferson/Unisexual Salamander in a trap at -1°C. I thought this salamander would be super lethargic given how cold it was, but it surprised me again by being very feisty. As if that wasn’t remarkable enough, we also found an Eastern Red-backed Salamander that evening that had ice formed on the outside of its skin. I worried that it was dead, but it almost immediately warmed up in my hand, broke free of the ice on the outside of its skin, and started walking around. This year we got photos of Jefferson/Unisexual Salamanders on ice pellets and snow and had our highest numbers of Jefferson/Unisexual Salamanders on both evenings. How incredible that these animals can still be so active when temperatures hover around freezing!