There is a lot of info out there, but the short version, as I understand it, is this: Veiled chameleons occupy a very niche environment in Yemen, called wadis (wadi, singular). Wadis are microclimates within the larger arid environment where seasonal rivers turn small pockets of otherwise desert land into lush, green forests. Moreover, the humidity in these wadis is reported to reach as high as 99% overnight, and drop below 30% during the day—something that is in keeping with the high temperature swing. The veiled chameleon lifecycle has evolved along side these wadis. Babies are born in the beginning of the wet season, reach sexual maturity by 4 or 5 months, mate, lay eggs, and then most die off at the onset of the dry season. So, to make a long story short: veileds are said to require humidity (some say only at night) because their niche habitat does, in fact, get very humid...or so I hear.