In the perpetual gloom of the Biblical Zoo's Underworld Exhibit resides a colony of naked mole-rats. If the phrase "naked mole-rat" sounds unappealing then these rodents live up to their name. Small and hairless, these roly-poly pug-faced creatures look like leftover dough. But despite their appearance, mole-rats are full of surprises. Naked mole-rats are found in dry areas of savannah regions near the equator such as Kenya, Somalia and Ethiopia. Serious scientific research about these rodents only began some 30 years ago and there is still much about mole-rats that remains a mystery. For instance, zoologists are not even sure how long the rats live. There are mole-rats that have been living in laboratories for over 20 years. They live in subterranean colonies that can number 200 individuals. They spend their whole lives underground digging complex tunnel systems to house the community. Curiously, they have a strict social structure that is very similar to that of ants. One mole-rat is selected to be the queen and she chooses a few male rats to be her suitors. If the queen dies, another female takes her place. Exactly how the queen is chosen is unclear but once a queen has been nominated she grows until she is one-and-a-half times the size of the other rats. The rest of the rats, both male and female, maintain the tunnels, keeping them clean of debris and collecting food to bring to storage areas. They can be seen hard at work all day long, unless they happen to be taking a brief siesta. Meanwhile, the queen and her entourage are kept busy producing more rats. The queen is only ever in two states, pregnant or giving birth, leaving one to wonder if royalty is indeed a privilege. Each gestation cycle is about 70 days and produces anything from three to 27 offspring. The burrow system is divided into specially assigned areas for food, sleeping, the queen's quarters and "public toilets" located at the end of tunnels. In the wild, the rats build tunnels by chewing their way through the ground using their powerful front teeth and their lips to prevent them from choking on the dirt. In the zoo the rats are housed in a specially constructed plastic pipe system. The tubes are only about as wide as a rat and passing is accomplished with frantic pushing, stamping and squishing together. When things get too tight and a tunnel or turn is too congested, the rats resolve the problem by running in reverse - a mode of locomotion of which they are just as capable as moving forward. Even a busy mole-rat needs some rest and every now and then the rats put down their tools and go to sleep, huddled together in cozy piles. Spending their whole lives in the dark the rats are almost completely blind, but research has shown that they navigate their tunnels using the earth's magnetic field and by drumming on the tunnel walls to send messages to each other. The zoo's collection of 16 rats is about to grow as the queen is ready to give birth. The network of pipes is large enough to house the current colony, and there is room for expansion for a community of up to 100.