Ventral marking gland, gerbil
Adult gerbils weigh 2 to 3 ounces (50 to 90 grams). Males are slightly larger than females. The coats of gerbils in the wild are agouti colored, or a mix of gray, yellow, and black, with an off-white belly. Breeding has produced gerbils with many different coat colors, including black, buff, white, gray, and spotted. They are about the size of mice, with their bodies measuring about 4 inches (10 cm); their fur-covered tails can add an additional 3 inches (8 cm). Gerbils typically live for 2 to 3 years.
Both male and female gerbils have a ventral marking gland on their abdomen. The gland appears as an orange-tan hairless area that is usually oval in shape. It can sometimes be mistaken for a tumor. In male gerbils, the gland enlarges during puberty and produces an oily secretion. Male gerbils may use this as a way of marking territory, and they can sometimes be seen rubbing their abdomen on objects.