Naked Mole Rat (Photo by Jessie Cohen)

Margie Gibson - NZP Staff Writer

The Zoo's Small Mammal House has become home for three Palestine mole rats (Spalex ehrenbergi), chubby, furry, six-inch long cylinders that bear a strong resemblance to a paint roller. These peripatetic rodents, native to Mediterranean coastal areas of northern Israel and Egypt, are a new species for the National Zoo. One of these Middle Eastern natives, a male, is on exhibit to the left, just inside the entrance to the Small Mammal House and two others, females, have a temporary home in the keepers' area out of the public's view, just behind the mole rat on exhibit.

Bill Xanten, collection manager of Small Mammals, was introduced to the species on a visit to the Philadelphia Zoo last spring and was impressed enough by their constant activity to propose that the Zoo add the species to its collections. While a few North American zoos have these tunneling rodents in their collections, Xanten believes that only ours are on public view.

Keepers have created comfortable "digs" for these burrowing animals in three 20-gallon aquariums. The floor of the aquariums has been covered with wood shavings and a number of acrylic tubes have been used to connect the large tanks and provide hiding places. The mole rats, very solitary in nature, each have separate enclosures where they spend their days burrowing under the wood chips, carrying pieces of food to secret caches for storage and exploring their enclosure. As they scurry through the tubes, they kick up an impressive amount of chips behind them with their legs.

Palestine mole rats weigh between four and eight ounces and are entirely covered by a heavy coat of fur. Vestigial eyes have disappeared completely beneath the skin and are barely visible, so it is difficult to determine which end of the animal is which! Even so, look carefully at their heads, because they are wonderfully adapted to their tunneling life in a subterranean environment. Blunt heads serve as shovels, helping to push dirt out of the pathways as the animals excavate through the ground. Their noses are padded with a fingernail-like substance and are used as tools to pack dirt into the tunnel walls. Strong muscles connect the head and body and reinforce the bulldozer-effect of the head. Those muscles also result in a neck almost as wide as the body, thus contributing to the cylinder-like appearance. The ears lie comparatively far back on the head and their external openings are very small-look carefully and you'll find them.

These solitary animals normally come together only during the breeding season, November through January, which is the rainy season in the eastern Mediterranean. Zoologists suspect that the cooler temperatures, which average between 40 and 50 degrees F., and the increased dampness in the soil may trigger breeding behavior. To date, the animals have bred only in the wild, so Small Mammal House keepers will be especially interested in trying to replicate natural conditions to see if successful births occur.

Tunnel systems in their native habitat are often found in close proximity and may even be interconnected, but the animals don't cross into each other's territory. Burrows are extensive and include living, sanitation, and storage rooms as well as chambers used for sleeping. Resting chambers are usually found in above-ground piles of dirt mounded up from tunnel excavations. Total length of the tunnel in a burrow system may vary between 213 and 640 feet.

The favorite foods of the Palestine mole rats are roots, bulbs, and tubers, although the Zoo residents eat almost any fruit or vegetable. Considering their diminutive size, they have healthy appetites. In the wild, almost 40 pounds of potatoes and sugar beets have been found stockpiled in one of their burrows. Due to both their choice of food and the quantity they eat, mole rats can be a problem to farmers if they establish tunnel systems in an agricultural area. On the other hand, mole rats are a boon to archaeologists, a very common species in the Mediterranean region, because their burrowing unearths sherds of pottery and other fragments of former civilizations, thus guiding archaeologists to the best sites to dig for the remnants of earlier human habitation.

Encounters between members of the same sex or during the non-breeding season frequently result in injury or death to one or both of the animals. Their constantly growing, large incisors, so well-suited to excavating tunnels, provide a strong hint of the potential injury they could inflict on an unwelcome intruder.

Because members of this species are loners and meetings tend to be violent, communication is important, both to warn off potential confrontation as well as to signal readiness for breeding. Mole rats that share a tunnel system can warn off other inhabitants of the species with sound and smell, but mole rats in near-by tunnels have developed an alternative form of communication and seem to signal each other by head drumming. Israeli researchers studying Palestine mole rats created enclosures that simulated their natural homes by using Plexiglass tubes which the animals used as tunnels. Zoologists observed that the mole rats would occasionally enter the tubes and tap the upper front part of their head between one to twelve times on the tube's ceiling . This "head drumming" occurs in a series of bursts that result in vibrations which may travel through the ground and be sensed by other mole rats. Field studies have shown drumming occurs in a pattern very similar to the behavior observed in more controlled situations.

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Two years ago Zoogoer ran an article about Marty Condon, a biologist studying Heliconia butterflies. The butterflies' life cycle depended on supplies of passion flower and gurania plants, the latter of which is a member of the cucurbit family and includes gourds and squashes. In Peru in 1987 she collected a number of these tropical plants which she brought back to Washington and raised in a small nursery on the roof of the Reptile House. Before Marty left the Zoo, Dennis Davis, keeper in the Small Mammal House, caught her contagious enthusiasm for plants, and ended up falling heir to her collection, which he has propagated for use in the Small Mammal House.

Over his four years working there, Davis had grown interested in providing the animals he took care of with a variety of living plants which he believes benefit not only the animals by stimulating their curiosity but human visitors as well because the plants add beauty and interest to the exhibit. The products of Davis' effort can be seen throughout the Small Mammal House, particularly in the large exhibit at the back where the sloth and golden lion tamarins cavort amidst bougainvillea, passion flower vines, bromeliads, hibiscus and ficus trees. Be sure to notice the small clawed otter exhibit, where passion flowers and bromeliads bloom, and the golden headed lion tamarin enclosure with its tall, lacey stalks of papyrus.

Because of the close proximity of the animals, Davis realized he had to be cautious about using potentially harmful pesticides or fertilizers and he seized upon the opportunity to explore alternatives to chemical poisons: he decided to fight bugs with bugs.

Condon had already warned him of problems with whiteflies and aphids, and when Davis acquired the collection, both the gurania and passion flowers were supporting flourishing populations of nematodes and spider mites. To reduce the infestation, he took cuttings from the original plants and discarded the soil and remainders of the plants. After treating the cuttings with plant hormones, he planted them in a terrarium where they rooted under controlled humidity and temperature levels. Once the cuttings rooted, he set up a large trellis on a wall in the work area of the Small Mammal House and planted the young vines. Then, from these plants, he made more cuttings, which found their way to the exhibit areas.

Insect pests persisted, though, and soon shipments of predatory insects began arriving at the Small Mammal House. Armed with battalions of tropical lady bugs (Cryptolaemus montrouzieri ) and lacewings (Chrysopa carnea), and regiments of praying mantises (Tenodera aridifolia sinensis), predatory mites, and whitefly parasites (Encarsia formosa), Davis began battle with the insect pests. According to battle strategy, the tropical lady bugs have been munching on mealy bugs and aphids, while predator mites are subduing spider mites. Davis is enthusiastic about the outcome of the experiment and says that even nearby plants are reaping the benefits of the predatory insect treatment. He plans to continue using the insects warriors, although he wants to try hatching the lacewings under more controlled conditions. The first batch was hatched in an enclosure housing monkeys, who ate some of the eggs before they hatched! He also has an additional weapon in mind to fight whiteflies: spiders from Madagascar. Several years ago NZP director Michael Robinson returned from a trip with golden web spiders (Nephila madagascariensis), which took up residence in the Invertebrate Exhibit. Davis hopes their offspring, when they're released in the Small Mammal House, will eat some of the whitefly population.

Davis was also reluctant to use chemical fertilizer since it allows accumulation of salts in the soil which can create problems for both plants and animals. He found an alternative close at hand: Ed Gould, curator of mammals, has a collection of star-nosed moles, which is stocked with worms, a tasty delight in mole cuisine. Davis uses the steady supply of worm castings as fertilizer and reports that the plants are thriving.

He's experienced a few frustrations in giving the animals access to plants and has come to realize that there is an art to matching the right plants with the right animals. Davis expects that ever so often, animals will tear up plants. Once, for example, he found a dead-looking plant, nursed it back to health and was delighted when it turned out to be a large hibiscus. He moved it into an enclosure housing sloths and titi monkeys, and was dismayed when the animals chewed off all the leaves, reducing the plant once again to a bare state. He quickly realized though, that the animals' environment had been enhanced by the added interest the tree provided and realized that living browse could benefit more Small Mammal House residents.

He is expanding his botanical efforts to nearby outdoor areas housing maras, squirrels and golden lion tamarins. He hopes to establish year-round stands of bamboo and evergreen that will provide the animals with new challenges and surprises.

Perhaps Davis's efforts to grow the gurania will be a pivotal connection in the fight against AIDS. Hector Flores, an associate professor of plant pathology at Penn State University in State College, recently obtained cutting of the guranias from Davis' plants. Flores was interested in his university's research on the tuberous root of the Chinese medicinal cucumber, Trichosanthes kirilowii, also known as the snake gourd and a member of the cucurbit family. Practitioners of traditional Chinese medicine used the plant to induce abortion and regulate irregular ovulation in humans. Studies of the plant revealed that its root proteins inhibited replication of HIV and scientists are now trying to determine if those proteins might also be used to control AIDS.

Flores, from South America, knew that the gurania, also a member of the cucurbit family, was used by Indians for practically the same purposes that the Chinese used the medicinal cucumbers. Thanks to Davis who kept the gurania growing long after Marty Condon completed her butterfly project, Flores was able to obtain cuttings which he is now trying to establish at Penn State. Soon he hopes to begins studies to see if gurania, too, might have pharmaceutical properties useful to the fight against AIDS.