I worked in a kitchen for several years, as did (and do) many of my friends, and I know from experience that keeping all flies out of the kitchen is nearly impossible, no matter how clean your kitchen is, how many fly paper strips you hang, and how many UV bug catching lights you have. A combination of produce, garbage, dishes, trash, open doors, and light bring bugs in.

I often don't make a big deal out of these things. If it was clear the bug had been cooked into or on my food, I may or may not return it. For example, my mother once got a hamburger from Wendy's with a weevil baked on top. She returned it, however, I know that that style of baking, anything on the fly or anything the fly was carrying would remain in the area the fly was - I'd just pick it off the bun and go on my way. I have actually eaten soup that had a fly in it before. It was clear the fly landed in the soup after it was brought out, so I just scooped it out and that was it. I do the same with hair - it's no big deal.

However, if it's something like soup where it's clear to me the bug has been cooked in and stewed around to touch all of the food, I would likely return it. It's not that I would fear for my safety, but simply that it would upset my appetite. I don't worry about most things like that, to be honest. The number of bugs, or parts of bugs, or rodent hairs in processed food is immense. I've never been injured from it, so what's the big deal? I hardly doubt anyone is going to get sick and die from a bug that touched something adjacent to their food!

http://www.cartoonstock.com/newscartoons/cartoonists/dpa/lowres/dpan1745l.jpg

Unless the soup was the only dish in the meal, I think I wouldn’t complain and that I would just skip the soup that time. I understand that not everyone has bad intentions, but I usually don’t send my food back unless there is something really wrong with it. I would hate to offend anyone by sending my food back for something like a fly in my soup. I know that I definitely wouldn’t eat the fly, because I get too squeamish, and there is no way that I can knowingly eat a fly after discovering it in my soup. A few years ago, my husband had me watch a movie called “Waiting” that scarred me forever. I don’t think I’ve sent any food back since!

You should notify the waitstaff. Be courteous but something foreign in any food may be an indicator of things not quite right in the kitchen. A house fly is potentially nasty as they can carry disease causing material such as bacteria and deposit it on food. It is important that when you report the problem you be courteous but firm getting agitated or showing anger or discourtesy may result in the fly being removed and the same food brought back out to you. Be sure to tell them your concerns but don't try to assign blame just let them know you would prefer a fresh serving. Things happen and this may be just a simple problem but if the staff are made aware of it then hopefully they will take steps to insure it is less likely to happen in the future.

What would a Vegetarian do.

I would complain, because fly's land on faeces, and could spread potentially deadly germs to my soup.

You tell the waiter and leave the restaurant. This is the sign of a dirty kitchen if it comes out like that.