how do I stop insects (thunder bugs) getting in my screen?

yet again I have had a number of thunder bugs invading my screen and then being overcome by the heat and now they are dead!

I'm still in warranty so know that Apple will sort it for me as they did last year, but I want to stop it for when I am out of warranty next summer.

The technician told me that they enter through the vent at the back attracted by the heat and then the light of the screen. He said that they might enter through the usb and other slots at the back. I now have about 20 dead bugs spoiling my lovely mac...

any thoughts? a fine mesh stuck over the back??

I can't be the only one that suffers this!