Eastern Red-Backed Salamanders and Common Woodlice

I live in New England, USA, and during a few of my recent log-flipping adventures, I have found Oniscus isopods (suggested to both be O. asellus by a friend) always relatively close to Eastern Red-Backed Salamanders under logs - this is the only time I really see this species and so far they’ve both been notably close to the salamander. Has anyone else seen these two species close to each other? If so, might this be some form of mutualism or just that the area they’re sitting in happens to be the best spot, or maybe something else? I know this species of isopod is an invasive in New England, so this might just be correlation and not causation. If any of you have any insights or have seen similar things, please share here!
Observations here + isopod and here + isopod


Yesterday, I was emptying some big ceramic pots in my garden, ones I fill with annuals each year. The pots sit on top of big spruce stumps. When I moved one pot off its stump, there were three red-backed salamanders and dozens of isopods underneath. I think they just like the same habitats: damp, sheltered, dark. I wondered if the salamanders eat the isopods, particularly the young ones, but I haven’t gotten around to looking that up yet.


While I’m not familiar with Oniscus isopods specifically, I would assume this is due to similar microhabitat requirements rather than some form of mutualistic interaction.


Oniscus and redbacks like the same wet logs, bricks, and cooler temps


I would agree, they have similar microhabitat requirements. Plethodon cinereus is a predator of Oniscus asellus so their relationship is not mutualistic.


I’m sure isopods are one of their main sources of food. We have the nearly identical Ozark Zig-zagged Salamander here. I have found no correlation with their presence and roly polys.

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