Naked Mole-rat (Heterocephalus glaber) Fact Sheet: Physical Characteristics

Body measurements

*Note: Adults in managed care typically 30 to 50 g (1 to 2 oz), sometimes 80 g (3 oz) or more (Jarvis and Sherman 2002)

Data sources: Brett (1991b), Patterson (2016)

Body

• Body size (Jarvis and Sherman 2002)
  • Smaller than other African mole-rats
  • Weight of nonbreeding males and females similar
• Skin
  • Coloration pink (Daly and Buffenstein 1998; Patterson 2016), brownish pink (Jarvis and Sherman 2002), or brownish-purple (Tucker 1981)
    • Young workers (less than 7 years old) have darker back (Braude et al. 2001)
  • Loose and folded (Thigpen 1940; Tucker 1981; Daly and Buffenstein 1998)
    • Reduces abrasions
    • Allows easy movement in confined or crowded burrow spaces
      • Common adaptation in animals that live underground
    • Thicker on face
  • Nearly hairless (Hamilton 1928; Thigpen 1940; Hill et al. 1957; Crish et al. 2000; Patterson 2016)
    • Body covered by coarse sensory hairs
      • Most dense around head and mouth
      • Adaptation for tunnel navigation in darkness
  • No insulating fat layer (Daly and Buffenstein 1998)
    • See “Thermoregulation"

Head and mouth

• Mouth (Hamilton 1928; Jarvis and Sherman 2002; Patterson 2016, and as noted)
  • Front teeth (incisors) large and curved; protrude from mouth
    • Used for tunnel digging
    • Grow continuously (Berkovitz and Faulkes 2001)
    • Sharpened when upper/lower incisors scrape against each other
  • 2 to 3 upper and lower cheek teeth
  • Tongue thick and cylindrical (Hill et al. 1957)
• Jaws (Cox and Faulkes 2014)
  • Adapted for digging
  • Muscles very large
    • Weigh one-quarter of an individual’s body mass
  • Bite force strong
  • Gape very wide
• Eyes (Jarvis and Sherman 2002, except as noted)
  • Small
  • Usually kept shut, unless alarmed (Jarvis 1991)
  • Eyelids thickened
  • Eyelashes small
• Ears (Patterson 2016)
  • Small
  • Raised ring of skin around ear opening (Mason et al. 2016)

Legs and feet

• Short and slender (Hamilton 1928; Jarvis and Sherman 2002)
• 5 digits on each foot (Hamilton 1928)
• Claws short (Hamilton 1928)
• Sensory hairs on feet and between toes (Hamilton 1928)

Tail

• Long, compared to other African mole-rats (Jarvis and Sherman 2002)
  • Longer than hind foot

Little sexual dimorphism in nonbreeding individuals

(Hagen 1985, as cited by Jarvis 1991; Jarvis 1991)

• Sexual organs visibly similar
• External genitalia structures very similar; faint dark-red line between clitoris and anus present in females
• Under certain conditions, nipples (mammae) may be present in both sexes
• Testes undescended in males; lie in abdominal cavity
  • Other internal structures small and undeveloped
  • About 75% of adult males produce sperm, though only 1 to 3 mate

Also see Communication.

Touch

• Sensory hairs (vibrissae) allow fast navigation through underground tunnels (Thigpen 1940; Hill et al. 1957; Crish et al. 2000; Patterson 2016)
  • Hairs on head and tail particularly important

Smell

• Nasal structures for detecting pheromones relatively small (Smith et al. 2007; Dennis et al. 2019)

Hearing

• Limited (Heffner and Heffner 1993; Mason et al. 2016; Patterson 2016)
• Thought to be attuned for low-frequency sound (lower than 3 kHz) (Credner et al. 1997; Mason et al. 2016)
  • Travels better underground than high-frequency sound

Vision

• Poor (Crish et al. 2006; Němec et al. 2008)
• Basic mammalian eye structures (cornea, lens, retina) present but reduced (Nikitina et al. 2004; Hetling et al. 2005; Němec et al. 2008)
  • Development, anatomy, and arrangement differ from mammals that depend on vision
• Sense light but not images or shapes (Crish et al. 2006; Němec et al. 2008)
  • Possible adaptations of light sensitivity
    • Detect holes in burrow; plug holes
    • Determine when near surface or outside burrow
    • Regulation of circadian or seasonal rhythms (Riccio and Goldman 2000)
• Not able to orient themselves aboveground (e.g., for navigation) (Němec et al. 2008)

Metabolism and energy production

• Low metabolism, relative to body size (Yahav and Buffenstein 1991a)
• Capable of reducing metabolism when food is scarce (Goldman et al. 1999)
• High production of energy in certain tissues maintained through early adulthood (Holtze et al. 2016)
  • Does not decline, as observed in other rodents

Thermoregulation

• Body temperature fluctuates with surrounding environmental temperatures (usually burrow; range: 12 to 37°C, or 54 to 99°F) (Buffenstein and Yahav 1991a)
  • Not regulated at constant temperature, like most mammals (Buffenstein and Yahav 1991a)
  • Sensitive to cold (Hill et al. 1957)
• Behavioral thermoregulation (Yahav and Buffenstein 1991a; Patterson 2016, except as noted)
  • Group members huddle together for warmth
    • May absorb heat more quickly by being hairless (Alexander 1991)
  • Select burrow chambers to gain or lose heat (e.g., warmer tunnels near surface)
• No sweat glands (Tucker 1981)

Nervous system

• Nociceptive (pain) system unique among mammals (Park et al. 2008; Patterson 2016)
  • Insensitive to chemical and inflammatory pain triggers
    • Lack pain-related neuropeptides in cutaneous sensory fibers
    • No pain behaviors in response to acid and capsaicin
  • Structure of and connectivity between peripheral nerves differs from other mammals
  • Unique pain adaptations may have evolved to cope with high CO₂ levels in cramped, poorly ventilated burrows
• Large brain areas associated with touch and movement of the mouth (Catania and Remple 2002; Henry et al. 2006)
  • Areas associated with vision reduced (Němec et al. 2008)

Respiratory and circulatory systems

• Lungs not well developed (Maina et al. 1992)
• Hemoglobin, the oxygen-transport protein in the blood, is able to bind an unusually large amount of oxygen (Johansen et al. 1976)

A naked mole-rat's body is covered in coarse sensory hairs that help it to navigate a maze of tunnels in the dark.

Large incisor teeth are used for digging and chewing through fibrous plant tubers.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.