Fogging will also occur if the camera is at a room temperature but will be less intense and should seize in about 20 minutes. All my equipment has survived aviary conditions many times without getting condensation inside of any lens. As precaution, I open the camera bags and turn the car heater up on the way to the aviary for at least an hour before the shoot. This is a rather heavy setup and my hands quickly loose their steadiness needed to keep the subject in the very limited depth of field. I have better results with one strong unit equipped with the Photoflex bouncer.
Black backgrounds look good with moths but artificial for butterflies.
To avoid them, whenever possible I meter the background and choose exposure 1 to 2 stops under this reading. This frequently means an f-stop close to f5.6 and very limited depth of field. Under these conditions, getting the whole winger in focus is the main challenge. In an indoor aviary there are so many butterflies that you may choose a flower, angle, and background and wait for the subject to land in front of your lens. There are several excellent field guides to North American species.