Naked Mole-rat (Heterocephalus glaber) Fact Sheet: Behavior & Ecology

Rest in large groups

• Colony active day and night (e.g., Brett 1991a)
  • Digging more common at night
• Nonbreeders spend substantial time resting (Lacey et al. 1991; Lacey and Sherman 1991)
  • Huddle together during periodic rest breaks; often sleep in a large “dogpile,” up to 4 individuals deep (Tucker 1981; Lacey et al. 1991; Patterson 2016)

Structure

• Burrow system composed of chambers and tunnels (Patterson 2016)
• Chamber functions (Jarvis and Sale 1971; Maree and Faulkes 2016, except as noted)
  • Nesting: care of young and food storage
    • Usually lined with peels of root vegetables and other fibrous materials (Hill et al. 1957)
  • Latrines: where urination and defecation occur
• Tunnel functions (Jarvis and Sale 1971; Brett 1991a)
  • Movement between chambers
  • Connection of nest chambers and shallow foraging areas
  • Soil removal from burrow
• Tunnels can extend 3 km (2 mi) or more (Patterson 2016)
• T-shaped tunnel junctions allow mole-rats to back in and reverse direction (Hill et al. 1957; Lacey et al. 1991)
• Tunnel structure influenced by food type and location (Jarvis and Sale 1971; Brett 1991a; Patterson 2016)
  • Extensive branching where food is concentrated
• After use, shallow foraging burrows sealed off from main burrow system (Brett 1991a; Patterson 2016)

Digging

• Most digging is cooperative (Hill et al. 1957; Lovegrove 1989; Brett 1991a; Patterson 2016, and as noted)
  • Most intense after rain softens soil, allowing for easier, more rapid expansion of burrow system
• Teeth and forelimbs used for excavation (Jarvis and Sale 1971; Tucker 1981)
  • Brace body with forelimbs
• Diggers form a chain (Jarvis and Sale 1971; Lacey and Sherman 1991; Patterson 2016, except as noted)
  • More dominant individuals excavate at front of chain (Brett 1986)
    • Periodically relieved by individual behind
  • Workers in middle of chain scrape and push soil under body (with front limbs, then hind limbs)
    • Soil eventually passed to individual at tunnel exit
  • Often a larger individual is at end of chain (Braude 1991; Lacey et al. 1991)
    • Expels soil from burrow using backwards kicks
• Digging activity leaves volcano-shaped soil mounds (molehills) aboveground (Drake-Brockman 1910, as cited by Hamilton 1928; Jarvis and Sale 1971; Braude 1991; Jarvis and Sherman 2002)
  • A colony of 85 to 90 mole-rats can produce 400 to 500 molehills (a displacement of about 3,600 to 4,500 kg/7,900 to 9,900 lbs of soil)
  • Holes on surface quickly covered to prevent snakes from entering (Jarvis and Sherman 2002)
• Individuals in managed care observed to place woody materials behind front teeth while digging in substrates that produce fine dust (Shuster and Sherman 1998)
  • Described as “tool use”
  • May help to prevent choking, or inhaling fine dust or shards of sharp materials
  • Not yet known if a similar behavior occurs in wild populations

Nesting

• Carry nesting material in teeth or sweep it to nest using hind feet (Lacey and Sherman 1991)

Colony distribution

• Local distribution
  • Colonies often adjacent or interconnected (Brett 1991b)
    • Naked mole-rats have limited dispersal ability
  • A colony of 60 to 90 individuals may occupy a burrow system of 0.5 to 3 km (0.3 to 2 mi) (Patterson 2016)
• Regional distribution
  • Patchy; colonies not often near each other (Patterson 2016)
  • Size of colony and proximity to nearby colonies influenced by food density

New colony formation

• Triggered by queen’s death or physical division of burrow system (e.g., tunnel collapse (Brett 1991b; Patterson 2016)
  • Nonbreeding individuals may remain sealed off in new colony to gain breeding status

Active dispersal

• Litters may include rare “disperser morphs” (O’Riain et al. 1996; O’Riain 1996; Braude 2000)
  • Active individuals, with fat reserves
    • May be of either sex
    • Travel aboveground 200 to 300 m (600 to 1,000 ft) or farther to mate with members of other colonies or start new colonies
    • Reduces inbreeding, promotes genetic mixing

Highly social within colony

• One of the few eusocial vertebrates (caste system) (Jarvis 1981; Faulkes and Bennett 2013; Maree and Faulkes 2016; Patterson 2016)
  • Characteristics (Jarvis 1981; Faulkes and Bennett 2001)
    • Reproductive division of labor
    • Overlapping generations
    • Cooperative care of young
  • Examples of eusocial insects: honey bees, termites (Lacey and Sherman 1991)
• Naked mole-rats live in highly organized colonies of extended family groups (Brett 1991b; Maree and Faulkes 2016; Patterson 2016)
  • Typically 40 to 80 (range: 10 to 295) individuals per colony
• Majority of individuals work but do not breed (Lacey and Sherman 1991)
  • Nonbreeders gather food, defend the burrow, care for young, and provide other support to the colony
  • Often referred to as “subordinates” (sexually immature adults)
• Dominance hierarchy based on body size (Brett 1991b; Lacey and Sherman 1991; Clarke and Faulkes 1998; Patterson 2016, except as noted)
  • Only largest individuals in colony breed
  • Duties of workers shift as they grow in size: from burrow maintenance and care of young to digging, searching for food, and burrow defense
  • Larger individuals have better access to resources (e.g., food)
  • Larger individual moves over the top of smaller individual when 2 individuals meet in tight tunnel spaces (Lacey et al. 1991)
• See Lacey et al. (1991) for descriptions of social behaviors
• See Reproduction

Tactile communication

• Shoving behavior reinforces dominance hierarchy (Reeve and Sherman 1991; Jacobs and Jarvis 1996; van der Westhuizen et al. 2006) and possibly several other functions (Reeve and Sherman 1991; Reeve 1992; Stankowich and Sherman 2002)
  • See Agonistic Behavior and Defense

Smell and scent marking

• Colony members identify one another by a unique “colony scent” (Reeve and Sherman 1991; O’Riain and Jarvis 1997; Jarvis and Sherman 2002)
  • Scent acquired during huddling, grooming, and when individuals roll in latrine chamber
  • Pups recognize queen by scent before eyes open (Jarvis 1991)
  • Also see Agonistic Behavior and Defense

Vocalizations

(Pepper et al. 1991; Credner et al. 1997; Patterson 2016, and as noted)

• Naked mole-rats very vocal (Pepper et al. 1991)
• Colonies have unique dialects (Barker et al. 2021)
  • The queen controls and reinforces the accent
  • Used to distinguish between members of the same colony vs. another colony
• Many types of calls (at least 18); one of the largest vocal repertoires of any rodent (Judd and Sherman 1996)
  • Greeting/contact
  • Mating
  • Aggressive
  • Distress
• Juveniles have distinct vocalizations (Pepper et al. 1991)
• Uses of high-pitched calls (Judd and Sherman 1996)
  • To bring foragers to location of newly discovered food sources
  • To solicit food or copulations
  • As alarm (defense of burrow)
• Functions of chirps (Yosida et al. 2007)
  • Reduce conflict
  • Strengthen association between colony members
  • Resolution of dominance hierarchy conflicts
• Vocalizations may also communicate:
  • Body size/dominance
  • Individual identity

Threat detection

• Sensitive to vibrations (Hill et al. 1957)
  • Remain still if detect movement nearby

Strictly territorial

• Aggressive towards naked mole-rats of other colonies (e.g., O’Riain and Jarvis 1997)
• Aggressive towards separated colony members that have lost distinct colony scent (O’Riain and Jarvis 1997; Clarke and Faulkes 1999)
• Nonbreeding individuals defend colony against intruders and predators (Hill et al. 1957; Brett 1991b; Lacey and Sherman 1991; O’Riain and Jarvis 1997; Patterson 2016)
  • Worker gives alarm call when intruder detected
  • Larger-bodied defenders block tunnel to prevent intruder from entering nest
    • Advance and retreat together, in unison
    • Gape and snap teeth
    • Give hiss or trill vocalizations

Confrontation within a colony

• Colony members compete for resources (Patterson 2016, and as noted):
  • Food (Schieffelin and Sherman 1995)
  • Access to dig sites
  • Breeding status, especially among females (Jarvis 1991)
    • Male–male aggression infrequent in established colonies (Clarke and Faulkes 1998)
    • Agonistic behavior (physical contests) suppresses reproduction in subordinate individuals (e.g., Margulis et al. 1995)
• Dominance often asserted through open-mouth gaping, accompanied by hiss and chirp vocalizations (Lacey et al. 1991; Patterson 2016, and as noted)
  • Additional behaviors (rarely cause injury)
    • Tugging skin of opponent (Schieffelin and Sherman 1995)
    • Shoving (Reeve and Sherman 1991; Margulis et al. 1995; Jacobs and Jarvis 1996; O’Riain 1996; Clarke and Faulkes 1998; Clarke and Faulkes 2001; Stankowich and Sherman 2002)
      • Breeding adults—particularly queen—shove pups
        • Most frequent during weaning
      • Queen shoves large and high-ranking individuals
    • Tetany
      • After being shoved by breeding female, subordinate individual lies still with feet in air for several minutes
    • Biting
• Same-sex fighting between subordinates to gain breeding status (Margulis et al. 1995; Clarke and Faulkes 1997; Smith et al. 1997; Ciszek 2000; Clarke and Faulkes 2001, and as noted)
  • Occurs after queen’s death (females) or during new colony formation (both sexes)
  • Often results in injury or death (Jarvis 1991; Lacey et al. 1991)
    • Competitors shove and bite each other
• Juveniles wrestle and spar by interlocking incisors (“tooth fencing”) (Lacey et al. 1991)
  • Also grip and drag each other through tunnels
  • Behavior ceases in adulthood

Grooming and self-care

• Mole-rats groom themselves, not each other (Tucker 1981; Alexander 1991)
• Clean feet, head, and body with incisors (Lacey et al. 1991)
• Sharpen incisors by grinding edges of top and bottom teeth together (Lacey et al. 1991)

Ecosystem engineer

• Hill et al. (1957) suggest burrowing by naked mole-rats allows rain and air to penetrate soil more deeply; promotes plant growth
• Burrowing activities of 2 other African mole-rat species shown to increase mineral levels in soil, and change plant species composition and richness (Hagenah and Bennett 2013)
  • Also affected aboveground plant biomass

Relationship with humans

• Naked mole-rats live in very dry regions with little development and little agriculture (Maree and Faulkes 2016)
  • Known to eat some types of crops (e.g., cassava, sweet potatoes)—but not a significant agricultural pest (Maree and Faulkes 2016)
• Atypical, highly developed social system is of much interest to biologists (Patterson 2016)
• Many adaptations and aspects of life history are of interest to medical/drug researchers (Patterson 2016; Mulatu 2018, and as noted)
  • Long life span/anti-aging traits (O’Connor et al. 2002; Dammann and Burda 2006; Edrey et al. 2011; Evfratov et al. 2014; Holtze et al. 2016; Lewis and Buffenstein 2016; Zou et al. 2020)
    • Good health maintained into late adulthood (O’Connor et al. 2002; Edrey et al. 2011)
  • Tolerance of hypoxia (condition of inadequate oxygen supply)
    • Video 1 (Smithsonian Channel)
    • Video 2 (The Atlantic animation)
  • Resistance to cancer (Liang et al. 2010; Jiang et al. 2016)
    • Cases reported from managed care populations (Delaney et al. 2016)
  • Insensitivity to certain types of pain (Park et al. 2008)
  • Genes as a biomedical resource (Keane et al. 2014)

Digging

• Large incisor teeth, primarily lower incisors, used for digging; also front feet (Tucker 1981)
  • Lip folds and bristles around mouth prevent soil from being swallowed (see Tucker 1981, p. 57)
• Also see Burrows

Running

• Can run both forward and backward very quickly (Tucker 1981; Lacey et al. 1991; Chris Faulkes, personal communication, 2019)
• Climb over each other when passing in tunnels (Tucker 1981)

Swimming

• Capable swimmers (Hamilton 1928)
  • “Dog paddle” strokes; scull with tail

Nonbreeding workers often rest while lying on their backs.

Colony members often sleep in a large "dogpile," up to 4 individuals deep.

Image credit: © Josh More/Flickr. Some rights reserved, CC BY-NC-ND 2.0.

Naked mole-rats are known for forcefully kicking soil out of the tunnel exit during excavation (also known as "volcanoing").

Diggers work together by forming a chain, and then scaping and pushing soil to the tunnel exit.

Image credit: © Markus Lilje/iNaturalist. Some rights reserved, CC-BY-NC-ND 4.0.