Caught this little guy poking around the shore with a net. Never stocked any and the pond has no inflow. Only other times I've seen one was early summer when we found one on the road (weird) and put it in the pond and 5 years back I caught one pulling out some vegetation and I put him in an aquarium. Importantly this was BEFORE aeration. My question is, what species and how did it get in my pond!

Looks like a Procambarus gracilis or Fallicambarus fodiens. Latter I do not think occurs that far north. I would like to see pecker parts to firm up guess.

Overland movement possible for both. More likely animal accessed pond by a series of horizontal burrows moving up hill from where is was bred. Fish like sunfishes and catfishes normally keep both species from getting to high numbers in a pond setting.

Here's a pdf link that may help. It's a bit tedious, but very well written...

https://huntfish.mdc.mo.gov/sites/default/files/downloads/crayfish_id_brochure_6-08_0.pdf

My best guess from this is white river crayfish.

PD, I'm not sure where you are in Wisconsin, but the white river cray does live in some of the southern sections...

https://nas.er.usgs.gov/queries/SpeciesAnimatedMap.aspx?speciesID=216

I have know these types of maps to be incorrect and/or outdated at times.

EDIT: I do know that the crawdads around my place perform an exodus at times. Usually during high rain events. So, I suspect that guy just meandered into your pond and likely has friends as well. I can recall one rather wet evening at my place when I kept very busy herding them out of my shop to keep from stepping on them. My shop is 50 yards from the creek and the pond is 50 yards on the other side of the shop. I'm not sure where they were coming from or going to as there paths were very haphazard, but they had definitely taken to moving about.

On further inspection it could be a virile (northern) crayfish or a red swamp crayfish but I'm too far north for those. Specifically I'm 30 minutes SE of green bay. Seems to not be a rusty crayfish which would be a relief as they are hated in my parts.

I am sort of trained in crayfish taxonomy. Based on what is shown in photographs, the animal is not of the genus Orconectes nor is it a White River Crayfish which work with almost daily.

Centrarchid, and so what genus is it?

Here's a link to Wisconsin crayfish...

http://watermonitoring.uwex.edu/pdf/level3/Crayfish_WI_ID_GUIDE_2012.pdf

Hope this helps. It would appear to be very young which would make it even harder to identify or if it has recently molted.

I suspect that it is not the type that travels to water for reproductive purposes only. I believe that reproduction happens in the spring/early summer for most crawdads.

Congrats you ruled out every possible crayfish! I will keep my eyes peeled for another one, preferably an adult, but no guarantees on being able to get another.

If what I think it is, then the same species will be abundant in lowland areas with open water only seasonally. Look for turrets / mud chimneys areas that are at least occasionally mowed. If you find them, go out after dark on moonless nights with a flashlight and shine down burrows.

You can catch them with a proper use of a shovel. If you find the crayfish and interested in capturing, then let me know so I can describe process.

Do you still have him? Probably not...Catch another and maybe you could get those "pecker parts" photo'd for Centrarchid. I hope it's of legal age for that sort of thing. I'm not even sure were to start looking for its privates.

After a little research on "gonopods" (AKA pecker parts), I figure Centrarchid must be more than "sort of" trained in crayfish taxonomy. Good to have you here Centrarchid!

No. I may or may not have "released" him by throwing him directly at 2 BG but I'm sure he's fine. He's just lucky no bass were around.
As far as looking for holes that would be next to impossible do to the swamp surrounding my pond. It has many islands and in total stretches between 5-10 acres.
If I catch another one I will take more pictures and imprison him until I know his identity.

I am also experienced in crayfish identification. Centrarchid is very likely correct the crayfish pictured is likely a burrowing specie of crayfish - in the genus Cambarus or Procambarus.
Here are the crayfish species listed for WI:
1.  Cambarus diogenes - devil crayfish
7.  Procambarus acutus acutus white river crayfish
8.  Procambarus gracilis prairie crayfish, rarest of the species in WI.
2.  Orconectes immunis papershell
3.  Orconectes luteus golden crayfish
4.  Orconectes propinquus northern clearwater crayfish
5.  Orconectes rusticus rusty
6.  Orconectes virilis northern crayfish

Could it be a devil crayfish? It fits the bill, burrowing and looks like the juvenile.

Something not right for the Devil Crayfish species complex. Several species in that and I am not sure which one is up that way. All have heavier looking legs than pictured and with the exception of the Nebraska version are more green. Better pic of rostrum / head reason needed.

It could be a devil crayfish. Look at stripe down the back. The Procambarus species lack that character. The one up there I am not familiar with.

Waffle like a politician.