mites.

[Amadeus]

Originally Posted by Starbuck

As AaronS said, they are attracted to something they need for survival, whether it be moisture, food, or a site to lay eggs. They are not attracted to the heat lamp.
Fruitflys often will commit 'suicide' and drown themselves in dishes of water... Leave a shallow pan out in your kitchen over the course of a day and you will see. I'm not sure why they do it, but they do.
overall, they arent causing an issue, you may just have them in your house and they made their way into your snake cage as they were looking for standing water.

since you just got this corn snake, its entirely possible that it COULD have had mites, if it is kept on newspaper or papertowel temporarily you will have a better idea of any unwanted passengers.

That's actually incorrect. Most flying insects are attracted to light and heat not just moisture and food.