I have two female leopard geckos and have had them about seven years. One, Zia, is your typical leo in build. The other, Zephyr, is much longer and leaner, her tail has never been very fat even when she was housed alone for three weeks and given as many crickets as she wanted. She's by no means emaciated, just lean. Both geckos are housed in the same tank and eat roughly the same amount, and there's no bullying going on. She's never had any health issues and is very active. Also, her tail is much longer than my other gecko's. Zia's tail is the same length as her body while Zephyr's is long as her body and her head combined. Anyone else have a leo that just doesn't put on weight?