Sudden phobia and hysterical over flies

Okay my son doesn’t seem to have any other fears, he loves animals and we go to the farm regularly. He even got pecked by a duck, cried for a little bit and then went back. He’s had the usual social anxiety but nothing that has been unusual. Yesterday I was in the kitchen and then he came crying and freaking out hysterically saying ‘bee bee’. I’ve actually never seen him like that, i was scared and thought he’d been stung or even swallowed it lol because he was holding his mouth. When he eventually calmed down, I thought maybe he didn’t articulate himself well and ‘bee’ was something else. Today, a fly was buzzing around inside and he had the same reaction. This time I was feeding him and he literally flipped up his plate and started crying hysterically again. I didn’t know what was happened but then he said ‘bee bee’ and then I realised he was scared of the fly. Now maybe I’m being naive but I thought those kind of fears were learned? As far as I’m concerned he hasn’t been stung by a bee. I’m not sure where this has come from. The thing for me is, if it was a dog fair, we see them far and few in between but right now, with the weather and the windows open, flies are bound to come in and out and of course I shoo them when I realise but his reaction and the aftermath is quite sad if I’m honest. Even in all is tantrums he’s never acted like this, he’s literally been so timid. It’s like his personality has changed, he won’t do any thing and wants me to carry him constantly or be touching me, his heads down. He’s throwing food, wee’ing himself (after successful potty training), literally so anxious looking around the room, doesn’t want to do anything, not speaking clearly, just low voice. I hope I’m not being dramatic but I’m confused and need some reassurance that it’s temporary or any tips to help. I don’t want to ‘coddle’ this fear as flies are everywhere.