Subfamily Spalacinae
blind mole-rats

Eurasian or Ukrainian blind mole-rats, the Spalacinae, comprise a relatively small subfamily of Old-World fossorial muroid rodents. There are 13 species in 1 genus, Spalax. (Musser and Carleton, 2005)

The range of Spalacinae extends around the eastern portion of the Mediterranean and the Black Sea, from the Balkans through Ukraine, Asia Minor, Syria, Palestine, and into Egypt and Libya. (Carleton and Musser, 1984; Nowak, 1999)

Spalacines live in moderately dense sandy or loamy soils that receive more than 100 mm of annual rainfall. They range from below sea level to above 2,600 meters, and they inhabit upland steppes, mountain valleys, agricultural fields, orchards, woodlands, river and lake basins, grasslands, and brushy areas. (Carleton and Musser, 1984; Nowak, 1999)

Spalacines have usually been classified separately from most other muroid rodents in the family Spalacidae (Alston 1879, Thomas 1896, Tullberg 1899, Miller and Gidley 1918, Ellerman 1940, Simpson 1945, Musser and Carleton 2005) or in an all-inclusive Muridae (Carleton and Musser 1984, Musser and Carleton 1993), but at least one author placed Spalacinae in the family Cricetidae (Chaline et al. 1977). Molecular studies support a basal position for Spalacinae among muroid rodents, in the family Spalacidae (Michaux et al. 2001, Jansa and Weksler 2004, Norris et al. 2004, Steppan et al. 2004). More molecular work is needed to clarify the relationships between spalacines and other spalacid groups.

Mole rats are not highly mobile and many isolated populations exist that are morphologically similar but differ in their number and arrangement of chromosomes. These cryptic sibling species, in addition to a high amount of convergence in fossorial adaptations, has made it difficult to understand relationships within the subfamily Spalacinae. Opinions have varied on the number of genera that belong in the subfamily, and six different spalacine genera have at one time or another been included: Microspalax, Pliospalax, Nannospalax, Mesospalax, Heramys, Spalax. Also, anywhere from three to over 14 species have been distinguished. Savic and Nevo (1990) suggest that naming only one spalacine genus is appropriate until a detailed molecular study is conducted, and they concede that the number of species in the subfamily is likely to change. Such a phylogenetic study is yet to be done, and for now, the species-level taxonomy of Spalacinae remains uncertain. (Alston, 1876; Carleton and Musser, 1984; Chaline, Mein, and Petter, 1977; Ellerman, 1940; Jansa and Weksler, 2004; Michaux, Reyes, and Catzeflis, 2001; Miller and Gidley, 1918; Musser and Carleton, 1993; Musser and Carleton, 2005; Nevo, 1999; Norris et al., 2004; Savic and Nevo, 1990; Simpson, 1945; Steppan, Adkins, and Anderson, 2004; Thomas, 1896; Tullberg, 1899)

Spalacines are chunky, molelike animals with short legs, small feet and claws, subcutaneous eyes, and external ears that have been reduced to tiny ridges. They range in length from 130 to 350 mm, and weigh 100 to 570 grams. There is no visibile tail. Mole rats have thick, soft fur that is nearly reversible, allowing the animals to easily back down tunnels. They have broad, cushioned snouts with which they pack earth into the walls of their burrows. There are stiff rows of tactile bristles running down either side of a mole rat's face. The fur color is brown, reddish, or yellowish gray, and the ventral parts are generally grayish or straw-brown. The front of a mole rat's head is paler than the rest of the body. The feet have a silvery sheen to them, and there are five digits on each foot.

The spalacine dental formula is 1/1, 0/0, 0/0, 3/3 = 16. The broad incisors are orthodont and project forward in front of the lips. The cylindrical cheekteeth are rooted and have an enamel pattern in the shape of a Z or an S. The rows of molars converge slightly posteriorly. The first two molars are about equal in size, and the third is slightly smaller. The jaw muscles, on which mole rats rely for digging, are extremely strong. Mole rats have heavy skulls and a wide rostrum, but the zygomatic arches are quite thin and delicate. The frontals are small and there are no supraorbital ridges. Adults usually have a sagittal crest. The thick-walled auditory bullae are somewhat inflated. Spalacines have 13 thoracic vertebrae and six lumbar vertebrae. The spalacine stomach is two-chambered and the cecum is divided into 18 to 20 chambers. There is no stapedial artery; rather, the infraorbital artery provides circulation to the orbits. Mole rats have a diploid chromosome number ranging from 38 to 62. (Carleton and Musser, 1984; Nowak, 1999)

Spalacines have a maximum lifespan of four and half years in the wild, and an average lifespan of about three years. In captivity, mole rats have been known to live as long as 15 years. (Nevo, 1999; Nowak, 1999)

Spalacines dig with their chisel-like incisors, pushing and packing earth with their broad snouts and kicking dirt out behind them with their hind feet. They build elaborate burrow systems with two levels of passageways: a top level for foraging, and and deeper level for living quarters. The top level passageways run 10 to 25 cm below the soil surface and can stretch for hundreds of meters. As mole rats dig these foraging tunnels, they push up mounds of earth that can stretch 500 cm wide. Mole rats also sometimes incorporate above-ground resting mounds into their burrow systems that connect to their foraging tunnels. The deeper passageways include one or two nest chambers, each about 20 to 30 cm wide and lined with plant material for bedding, and multiple chambers for food storage and excretion. These deeper chambers are usually 20 to 50 cm below the soil surface. However, mole rats dig even deeper during the hottest months of the year, when they are less active--they have been recorded as far 410 cm below the soil surface. Each mole rat burrow system displaces up to three tons of soil.

Mole rats are active at varying times of the day or night; they sometimes come above ground to forage under the cover of darkness. They are solitary, territorial, and aggressive towards intruders. The size of each mole rat's territory varies with the species, population, habitat, age, and sex. Population densities range from 0.1 to 23 mole rats per hectare. Most individuals in any given mole rat population are adults, and the sex ratio is skewed towards females. (Carleton and Musser, 1984; Nevo, 1999; Nowak, 1999)

Mole rats navigate their pitch-black subterranean environment by touch, and they also have acute hearing. Their middle ears are specially adapted to perceive low-frequency sounds, which travel well underground. Their sense of smell is thought to be relatively weak, but they do use pheromones to communicate and they can sniff out their food. They make a variety of grunting and hissing noises, especially when threatened. They locate one another during the mating season by rapidly drumming their heads against the ceilings of their burrows, creating seismic vibrations. (Nevo, 1999; Nowak, 1999)

Spalacines are herbivores that eat mainly roots, bulbs and tubers. When they forage on the surface from time to time, they consume grasses, seeds, stems, acorns, and a few insects. They store large amounts of plant material in their underground chambers. (Carleton and Musser, 1984; Nowak, 1999)

Owls are the most important predators on mole rats. To avoid predation, mole rats spend most of their time underground, and they can be aggressive when cornered. Also, their fur color is often correlated with soil color: mole rats in darker soils have darker fur, those in lighter soils have lighter fur. This suggests that visual predators exert a fair degree of selective pressure on mole rat populations. (Carleton and Musser, 1984; Nevo, 1999; Nowak, 1999)

Mole rats probably help to aerate the soil with their extensive digging activity, and they are consumers of various plant species as well as prey for owls.

Spalacines can become serious agricultural pests. (Carleton and Musser, 1984; Nowak, 1999)

There are no known positive impacts of spalacines on humans, except in their roles in healthy ecosystems they inhabit.

The IUCN currently lists five of the 13 species in this family as vulnerable: sandy blind mole rats (Spalax arenarius), giant blind mole rats (or Russian blind mole rats, Spalax giganteus), Balkan blind mole rats (or Bukovin blind mole rats, Spalax graecus), greater blind mole rats (Spalax microphthalmus), and lesser blind mole rats (Spalax leucodon). (IUCN, 2004)