BUMBLEBEE BATS (WORLD'S SMALLEST MAMMALS): CHARACTERISTICS, BEHAVIOR, CONSERVATION

BUMBLEBEE BATS

bumblebee bat

Bumblebee bats (Craseonycteris thonglongyai) are the world’s smallest bat and arguably the world's smallest mammal. Also known as the Khun Kitti bats and Kitti's hog-nosed bats, they occur in western Thailand and southeast Myanmar, where it occupies limestone caves along rivers, including Pung Chang cave near Phuket. Adults are about 2.9 to 3.3 centimeters (1.1 to 1.3 inches) in length and weigh two grams (0.071 ounces). The main competitors for the smallest mammal title are from small shrews; in particular, the Etruscan shrew may be lighter at 1.2 to 2.7 grams (0.042 to 0.095 ounces) but is longer, measuring 3.6 to 5.3 centimeters (1.4 to 2.1 inches) from its head to the base of the tail. [Source: Wikipedia +]

About the size of a large bumblebee, bumblebee bats were discovered by Thai zoologist Kitti Thonglongya in 1974. They are also known as Kitti's hog-nosed bat to recognize their discoverer and because of their pink, pig-like snout. They are found in the Bilauktaung mountain ranges in western Thailand mainly in the Sai Yoke, Kanchanaburi Province as well as in southeastern near the border with Thailand. Bumblebee bats prefer to roost limestone caves near the tops of the caves for warmth and be near bamboo forests to search their food. Bumblebee bats commonly forage in the upper canopy of the forest. Their lifespans are unknown but it is thought to be around five to 10 years based on the lifespans of other closely related bats. (Ward, 2004) /=\ [Source: Alexandra Burns, Animal Diversity Web (ADW) /=]

Bumblebee bats have a reddish-brown or grey coat, with a distinctive pig-like snout, with thin, vertical nostrils. Their ears are relatively large, while their eyes are small and mostly concealed by fur. Their teeth are typical of an insectivorous bat. Colonies range greatly in size, with an average of 100 individuals per cave. These bats mainly feed during short activity periods in the evening and dawn, foraging around nearby forest areas for insects. Females give birth annually to a single offspring.

Scientists believe that the populations in Myanmar and Thailand are not geographically interconnected. Both genetic and echolocation research shows them to be quite different from each other. The two groups may even represent separate subspecies or species. Pipat Soisook, a well-known bat expert and the mammal curator at the Princess Maha Chakri Sirindhorn Natural History Museum in Thailand, told Mongabay that the Myanmar and Thai bat populations — while separated by topography — are still presently morphologically (physically) alike. “We probably cannot assign them as [being] different species [as yet], but we know that they are at least under an ongoing speciation process,” he said. [Source: Jeremy Hance, Mongabay, December 13, 2016]

Bumblebee Bat Characteristics

Bumblebee bats range in weight from 1.7 to 2 grams (0.06 to 0.07 ounces) and have a head and body length that ranges from 2.9 to 3.3 centimeters (1.1 to 1.3 inches). The length of the bumblebee bats’ forearms are 2.2 to 2.6 centimeters (0.8 to 1 inches) Sexual Dimorphism (differences between males and females) is not present: Both sexes are roughly equal in size and look similar.[Source: Alexandra Burns, Animal Diversity Web (ADW) /=]

bumblebee bat range in Thailand and Myanmar

Bumblebee bats have small eyes that are mostly hidden by fur. They have 28 teeth, which includes relatively large incisors. The lower incisors are long and narrow. The upper body of bumblebee bats is usually either brownish red, or gray. Their underside is paler color. Their wings and uropatagium (membrane between the forelimbs and hindlimbs used for gliding) are darker.

Alexandra Burns wrote in Animal Diversity Web: Bumblebee bats have a few distinct characters. First, bumblebee bats do not have a tail even though they have two caudal vertebrae. Their uropatagium (membrane between the forelimbs and hindlimbs used for gliding) are rather large. Their noses are pig-like, with large nostrils separated by a wide septum. Finally they also have large ears that are nine to 10.2 millimeters long. The tragus is around half the size of the ears. Females have two sets of nipples, one on the chest and the other in the pubic area. The nipples in the pubic area are thought to be vestigial or not fully developed. The males have a large swelling in the gland that is at the base of their throats. The wings of bumblebee bats are long and wide, making them well adapted for hovering. They have thumbs that have claws. Their hindfoot is slender, narrow, and long. Nowak described bumblebee bat skulls as small with a large inflated spherical braincase and lacking lambdoidal crests, postorbital processes, and supraoccipital ridges. In both genders a sagittal crest, which is a bone that runs down the top middle of the skull, is visible. The zygomata, which is the arch in the cheek, is described as slender but complete. /=\

Bumblebee Bat Behavior and Reproduction

Bumblebee bats are troglophilic (live mostly in caves), crepuscular (active at dawn and dusk), motile (move around as opposed to being stationary), and have daily torpor (a period of reduced activity, sometimes accompanied by a reduction in the metabolic rate, especially among animals with highmetabolic rates). Bumblebee bats only fly about one kilometer from the cave to forage. They do not maintain or defend territories. [Source: Alexandra Burns, Animal Diversity Web (ADW) /=]

The behaviors of bumblebee bats are similar to species within the families Megadermatidae, Rhinopomatidae, Hipposideridae, and Rhinoolophidae. They are normally active around dusk and dawn. The duration of dawn activity averages around 18 minutes while at dusk the average time is 30 minutes. When bats are not flying they are thought to be in torpor to conserve energy.

Typically, about 100 individuals of this species will share the same cave. Despite this congregation, bumblebee bats are not social. Mothers will roost alone in the nursery cave. /=\

Little is known about the mating habits of bumblebee bats. They engage in seasonal breeding and have one offspring per year and breed in late April to May. The average time to independence is one year. Parental care is provided by females. Pre-weaning protection is provided by the female. /=\ While inside the cave offspring are usually found attached to the mother. While the mother is foraging the offspring is left alone. (Kurta and Kunz, 1987; Nowak, 1999) /=\

Bumblebee Bat Echolocation and Feeding

roosting bumblebee bat at a cave in Thailand

Bumblebee bats communicate with sound and sense using touch, chemicals usually detected by smell and echolocation (emitting sound waves and sensing their reflections to determine the location of objects). Nothing is known about how the bats communicate within their roosts. [Source: Alexandra Burns, Animal Diversity Web (ADW) /=]

Bumblebee bats use echolocation to navigate their environment and hunt for prey. They use sounds of a high intensity and have a constant frequency lasting as long as two milliseconds followed by a shallow downward sweep lasting a duration of one millisecond. The beginning of the call has an upward sweep. The bats have a base frequency of 35 kHz. They also use two other harmonics. The second one is at 70 kHz and the third one, which is weaker, is at 105 kHz. /=\

Bumblebee bats are primarily insectivores (eat insects) but are also recognized as carnivores (eat meat or animal parts). Animal foods include insects, spiders and other non-insect arthropods. They are aerial feeders, meaning they catch their prey while flying. They prefer to fly and forage along the tops of the bamboo trees./=\

Endangered Bumblebee Bats

On the International Union for Conservation of Nature (IUCN) Red List bumblebee bats are listed as Vulnerable. On the US Federal List they are classified as Endangered. In CITES (Convention on International Trade in Endangered Species of Wild) they have no special status. Although the bat's status in Myanmar, is not well known, the Thai population is restricted to a single province and may be at risk for extinction. The main threats are habitat degradation and disturbance of cave roosting sites and limestone extractions. Their foraging habitats have been deforested, resulting in less prey for the bat’s to hunt.

Jeremy Hance wrote in Mongabay: For 12 years, the bumblebee bat was listed as Endangered by the IUCN Red List, but in 2008 it was downlisted to Vulnerable due in part to the discovery of new populations, including ones across the Thai border in Myanmar. Surveys from 1997-2008 counted around 10,000 bats in 44 caves in western Thailand and five caves in Myanmar. The total population may be considerably higher, however, with researchers estimating the Thai population at around 45,000 individuals in a 2009 study presented in the journal Endangered Species Research. No one knows how many might live in Myanmar, since a more thorough survey there could not be conducted due to security issues. But experts believe the Myanmar population is probably quite small due to the bat’s specific microhabitat requirements.[Source: Jeremy Hance, Mongabay, December 13, 2016]

The bat has also been impacted by scientific collection, and also by their sale as souvenirs to tourists willing to pay for them. Outside the caves, rapid deforestation due to logging, agricultural expansion and the growth of human communities, remains the major conservation concern. The bumblebee bat is legally protected in Thailand, and a portion of its habitat is protected by parks. Conservationists have recommended improved protection and management of its roosting caves as well as broader protection of its foraging areas.

Bumblebee Bats Threatened by Druggies, Monks and Tourists

Jeremy Hance wrote in Mongabay: This tiny bat is threatened by human disruptions both inside its roosting caves, and in the forests where it forages. Conservationists say that monks using the caves for meditation, drug users escaping to caves for a fix, and tourists driven by the desire to see the bats, have all negatively impacted the species. Indeed, some grottos have been turned into “show caves,” leading to the destruction of bat habitat. “Ecotourism should be fine when tourists do not destroy or modify natural habitat,” explained Soisook. “However, in most cases, when promoting a cave as a tourist attraction [guides] usually modify the cave to make it more comfortable for the tourists.” [Source: Jeremy Hance, Mongabay, December 13, 2016]

If tourists venture into the caves to see the bats, then some impact is unavoidable, according to Soisook. The best way to mitigate this damage, he added, is to only allow tourists into “some big caves where human activities will not change micro-habitat much.” The number of tourists allowed into the various caves should also be regulated.

He noted that smoke inside the caves — whether from meditating monks or drug users — could significantly harm the bats. One small piece of good news: in Myanmar, monks have become cave protectors. The monks usually only use the cave entrances, and their presence tends to keep others away, including hunters, drug addicts and even mining companies that would destroy the caves for cement production.

Image Sources: Wikimedia Commons, Pipat Soisook, Mongabay

Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated January 2025