If the moths are inside the case itself, you do not want to suck up any moths from there with a vacuum. The reason for this is that a lot of air is getting passed through the hose, and there will be a high chance of generating a potential difference between the vacuum hose and the computer. Of course, this means that you are building static charge; and should you accidentally get the hose close to any remotely sensitive part of the computer, you've pretty much fried you computer.
I would also suggest Rushjet's idea of having a greater source of light in the area to attract moths away from the computer.
Jam it back in, in the dark.