Isopod ID?

[Ghoulsnake]

Collected from my backyard in Northern Jersey. I've found similar isopods (general "roly polys") near me that are similar in coloration/pattern but don't have the "skirt" that this particular one has. Doesn't ball up with gentle prodding either. If someone knows what this species is or can direct me in the right direction it is greatly appreciated!

 

[Jurdon]

Oniscus asellus. Never kept any myself but they’re fairly common and I hear they like more ventilation than the average pod. They’re also more susceptible to overcrowding, so more space/hides than usual are appreciated. The skirtless individuals you encountered were most likely some species of Porcellio, though I’m not familiar with NJ’s wildlife so I can’t specify for sure.

 

[Ghoulsnake]

Oniscus asellus. Never kept any myself but they’re fairly common and I hear they like more ventilation than the average pod. They’re also more susceptible to overcrowding, so more space/hides than usual are appreciated. The skirtless individuals you encountered were most likely some species of Porcellio, though I’m not familiar with NJ’s wildlife so I can’t specify for sure.

Thank you so much!! That is very helpful

 

[Ghoulsnake]

I actually went back outside and found 3 more! Was trying to find what I meant by the "roly polys" to confirm but I couldn't seem to find any. I was told they were some Armadillidium species but that very well could be incorrect.

Question: I know it's difficult to sex isopods because they're absolutely tiny but I know it can be done. I'm curious as to what these structures are or if it indicates that they're male or female? @Jurdon is this something you know of? I'm curious.

 

[Jurdon]

You do seem to have caught a more stereotypical “roly poly”, Armadillidium nasatum! I keep these, as well as the other non-Oniscus sp. you’ve found, Philoscia muscorum. I could go more in-depth on the care for these two (nothing much, really) but I’ll answer your question first. Isopods can be sexed ventrally, with males having more prominent pleopods (they look kinda like little, flat pairs of legs between the lungs) than females. Oniscus have been said to have fairly variable pleopod shapes, but your A. nasatum and P.muscorum shouldn’t be too difficult with a good photo or two. I can’t exactly tell from the photo you provided, but I will attach a sexing diagram that I used for reference until I was able to eyeball it. The pods used in this image I believe are Porcellio scaber, but the same general rule applies to all terrestrial isopods I know of.

 

[WildSpider]

You do seem to have caught a more stereotypical “roly poly”, Armadillidium nasatum! I keep these, as well as the other non-Oniscus sp. you’ve found, Philoscia muscorum. I could go more in-depth on the care for these two (nothing much, really) but I’ll answer your question first. Isopods can be sexed ventrally, with males having more prominent pleopods (they look kinda like little, flat pairs of legs between the lungs) than females. Oniscus have been said to have fairly variable pleopod shapes, but your A. nasatum and P.muscorum shouldn’t be too difficult with a good photo or two. I can’t exactly tell from the photo you provided, but I will attach a sexing diagram that I used for reference until I was able to eyeball it. The pods used in this image I believe are Porcellio scaber, but the same general rule applies to all terrestrial isopods I know of. View attachment 290316

In the diagram, is it the male on the right? Thanks in advance, Jurdon.

 

[Ghoulsnake]

You do seem to have caught a more stereotypical “roly poly”, Armadillidium nasatum! I keep these, as well as the other non-Oniscus sp. you’ve found, Philoscia muscorum. I could go more in-depth on the care for these two (nothing much, really) but I’ll answer your question first. Isopods can be sexed ventrally, with males having more prominent pleopods (they look kinda like little, flat pairs of legs between the lungs) than females. Oniscus have been said to have fairly variable pleopod shapes, but your A. nasatum and P.muscorum shouldn’t be too difficult with a good photo or two. I can’t exactly tell from the photo you provided, but I will attach a sexing diagram that I used for reference until I was able to eyeball it. The pods used in this image I believe are Porcellio scaber, but the same general rule applies to all terrestrial isopods I know of. View attachment 290316

God, my newbie is showing. Is it bad I thought they were all the same species? I could tell they were different, but I assumed they were just different life stages lol whoops.

So, if I have this right... the largest one is the Armadilidium nasatum and the smallest one is the Philoscia muscorum? And the one I caught previously and the new similarly sized one are both Oniscus asellus. Are there any factors that help you differentiate them? Ahhh, I hope this isn't too much that I'm asking for. Your help has been greatly appreciated

And I'll definitely try to get better pictures.

 

[Jurdon]

In the diagram, is it the male on the right? Thanks in advance, Jurdon.

Ah, yeah, sorry! Should have specified.

God, my newbie is showing. Is it bad I thought they were all the same species? I could tell they were different, but I assumed they were just different life stages lol whoops.

Hey we’re all here to learn, don’t beat yourself up! I know I still have a lot to learn too. Isopods tend to look the same throughput their lives, albeit they are smaller and whiter in coloration when they’re younger. Newborn isopods (AKA mancae) are almost entirely white! They color up with each molt, and reach sexual maturity before growing to their full size.

But yeah, you’re right in terms of ranking them by size equivalent to species. Nasatum are in the same genus as the common pillbug, Armadillidium vulgare. The main differences nasatum has from vulgare are their trademark pattern and the little “nose” on their face. All Armadillidium sp. can roll into a ball, hence “roly-poly”. P. muscorum have that trademark black stripe (though I’ve seem images of individuals lacking this) and skirted exoskeleton, are extremely fast and have a rather soft, delicate body. O. asellus is pretty large for an isopod found in the northeast, and they have a rather distinctive shape, though it can be hard to tell them from certain local Porcellio/Trachelipus species, two genera you’re likely to become familiar with (and mix up from time to time) if you continue collecting pods.

 

[Polenth]

So, if I have this right... the largest one is the Armadilidium nasatum and the smallest one is the Philoscia muscorum? And the one I caught previously and the new similarly sized one are both Oniscus asellus. Are there any factors that help you differentiate them?

I'll list out a few things. They're not the only things, but will cover a few common species.

Pleopodal lungs: You've already found these in your photographs. They've the little white spots at the back near the legs. You'll generally find two pairs, five pairs, or no pairs. Oniscus asellus has no pleopodal lungs. Porcellio species have two pairs. Trachelipus rathkii (often confused for the others) has five pairs.

Flagellal segments: Look at the last section of the antennae. This is the tip after the last joint/bend. If you look closely, you can see it's divided into several sections. Porcellio and Trachelipus rathkii have two sections. Oniscus asellus has three.

Outline: Woodlice have two main bits of their body. You can see the segments look a little different at the join. For some, these two bits form a continuous outline, so they look like an oval. For others, the back part is noticeably narrower, meaning there is a step in the outline. Philoscia muscorum has a stepped outline. Porcellio species, Oniscus asellus and Trachelipus rathkii have a continuous outline.

Uropods / Telson: The bits at the back are the uropods (the two sticky out bits each side) and the telson (the bit between the uropods). One where this is handy is telling apart Porcellio dilatatus (has a rounded telson) and Porcellio scaber (has a pointier telson). Also, ball-rollers like Armadillidium species have shorter uropods.

Texture: Porcellio laevis is very smooth. Porcellio scaber is rough with little bumps. When two species match in the other main ways, this can help. Philoscia muscorum is unusually shiny compared to everything else.

Head Shape: The shape of the head when viewed from the top. You don't need this for most, but it's useful for telling apart Porcellio scaber and Porcellio spinicornis. Porcellio spinicornis is rounded between the eyes. Porcellio scaber is more pointy. People often do these two by colour/pattern, but it doesn't help much when you get one with a weird pattern.