My outdoor cat has a swollen eye. Is it an insect bite or injury?

Hello. While the swelling is quite noticeable, he does not appear to be in any pain or discomfort. There is no discharge or tearing, & the eye looks very healthy. The problem, however, is I can not tell from a picture if this is just benign swelling from a possible insect sting, or if Bootz got into an argument with another cat & you have an abscess brewing. If it is just a sting, the swelling should be better tomorrow. If not, and the area is worse, firmer & warmer in the morning, then I would think this is a bite wound & Bootz may need antibiotics. See how he is in the morning & decide if he needs to be treated for a possible abscess. Thanks for contacting Petco Pet Education Center, formerly Petcoach.