Agree could well be from a bite - ticks especially will cause a nasty swelling in some horses
The 'bean' is more likely to cause difficulty urinating
Did he not have it when you viewed him at wherever he came from?
It is edema. Are you keeping him in a stall and he was used to being turned out? Turn him out where he can and will move around and recheck in 24 hours. Or ride him for about 45 minutes and check him. Some geldings do this just like some horses will stock up in their legs when stalled.
Myth #3: Swelling in the sheath and tail rubbing are signs that a horse’s sheath needs cleaning. When a sheath swells, it has nothing to do with the accumulation of smegma inside it. -Because of its location on the underside of the horse, it is simply a natural low point where excess fluid is drawn by the force of gravity. For example, an older horse with low protein levels in his blood or liver disease may experience fluid buildup, called edema or pitting edema—swelling that holds a depression when you press into it with your thumb—in the sheath area without exhibiting any other clinical signs. In such cases, the swelling likely will disappear if the horse is turned out or exercised, just as it would from the legs of a horse who stocks up when stalled for long periods of time.
Another common cause of sheath swelling is parasites. Parasites also make horses’ tails itchy. So if you notice your horse rubbing his tail and he has a swollen sheath, the latter condition isn’t causing the former. Both can be cured by deworming with an ivermectin-containing product.
ok i do not believe this is flea nor flys as we live in michigan and it's too cold for either. I have only had this horse for 3 days. He had this when I brought him home and he was not stalled other than overnight. He is let out everyday. And at my home he is never stalled he has free run to paddock and stall. If it is a bean and he needs to be cleaned will this do the trick or will he need vet assistance.