I have had a pair of U. henkeli since May and at the end of June she laid one egg that I believe to be fertile. I have my doubts though since it is on day 152, but theres no mold or denting or anything else. She has put out a pair of infertile eggs once a month every month since the first egg. The first egg has been the only one ever laid in the nest box, which is another reason I believe it is fertile. When I hold a flashlight to the egg it glows yellow, but I can see a faint outline of something in there, so I don't know, I guess I will just have to wait and see. All of my geckos are cooling now, so I have my hopes for fertile eggs after they are done cooling.