Lincoln has a swollen bump on upper arm

[Loudhouse2]

I noticed this morning when giving them food that Lincoln has a swollen red bump on his upper arm. I’m not sure if it could be from a mosquito or an ant? There doesn’t seem to be any bleeding or visible bite wound. He’s using the arm fine here at some photos and a video.
https://youtu.be/BN4z0f_g39k

[Diggie's Friend]

It could be the beginning of a bot; it's that time of year again.:klunk