What Does the Bumblebee Bat Eat? A Diet Deep Dive

The bumblebee bat, also known as Kitti’s hog-nosed bat (Craseonycteris thonglongyai), feeds on tiny insects and spiders, catching them in flight or plucking them from foliage near its limestone cave roosts. Weighing roughly two grams and measuring about three centimeters long, this is one of the smallest mammals on Earth, and its diet reflects that miniature scale. What it eats, how it finds its prey, and how much food that two-gram body demands are all more interesting than you might expect.

Small Insects and Arachnids Make Up the Entire Menu

Bumblebee bats are strict insectivores. Their prey consists of the kinds of invertebrates small enough to fit inside a mouth barely wider than a pencil eraser. Studies of fecal pellets and observations of foraging behavior have identified several recurring prey types:

Small flies: Dipterans, including midges and gnats, appear frequently in diet analyses. These soft-bodied insects are abundant near the rivers and streams that run through the bat’s habitat in western Thailand and southeastern Myanmar.
Bark lice: Psocids, the tiny insects often found on tree bark and leaf litter, show up regularly. They are slow-moving and easily gleaned from vegetation.
Small beetles: Micro-coleopterans round out the harder-bodied prey items. These are typically no more than a few millimeters long.
Spiders: Small arachnids are taken from foliage and possibly from webs, suggesting the bats do not rely exclusively on catching prey mid-air.
Other micro-arthropods: Parasitic wasps, ants with wings, and other tiny flying or resting invertebrates have been identified in dietary remains.

The common thread is size. Everything on the menu is extremely small, generally under a few millimeters. This makes perfect sense given the bat’s own dimensions and its jaw structure. Kitti’s hog-nosed bat has a distinctive pig-like snout and relatively weak jaws compared to larger insectivorous bats, so it targets prey it can subdue and swallow without a prolonged struggle.

Two Foraging Strategies Working Together

Bumblebee bats hunt using two complementary techniques. The first is aerial hawking, where they chase and catch flying insects on the wing. They emit high-frequency echolocation calls, listen for the returning echoes, and intercept prey in mid-flight. The second technique is gleaning, where they pick stationary or slow-moving prey directly off leaves, bark, or other surfaces. Gleaning allows them to access insects like psocids and spiders that do not fly or are resting.

This dual approach matters because it broadens what the bat can eat. A bat that only hawks in open air is limited to whatever happens to be flying at that moment. A bat that also gleans from vegetation can exploit a wider range of invertebrates, including those that are nocturnal but sedentary. For an animal as small as the bumblebee bat, having access to both hunting modes likely makes the difference between getting enough food each night and falling short.

The echolocation calls themselves are adapted to the bat’s size and habitat. Bumblebee bats forage in dense vegetation near the tops of bamboo clumps, teak trees, and other plants growing along rivers and at the edges of forests. Their calls are short, high-frequency pulses suited to detecting small targets at close range amid cluttered surroundings. A bat hunting in open sky might use lower-frequency calls that travel farther, but the bumblebee bat operates in tight quarters where short-range precision is more useful than long-range detection.

When and Where Foraging Happens

Bumblebee bats do not forage throughout the night. They emerge from their limestone cave roosts in brief bursts, typically during two narrow windows: one around dusk and another just before dawn. Each foraging bout lasts roughly 20 to 30 minutes. Between these bursts, the bats return to their caves and rest. This pattern is strikingly different from many insectivorous bats that forage more or less continuously for several hours each night.

The short foraging windows mean the bats need to be efficient. They cannot afford to spend half the night searching unproductive patches of sky. Their roosts are located in limestone karst hills close to rivers and streams in the provinces of Kanchanaburi in Thailand and parts of southeastern Myanmar. These waterways are insect-rich environments, especially at dusk when clouds of small flies and midges emerge. By roosting close to productive foraging habitat, the bats minimize commute time and maximize the fraction of each burst spent actually catching prey.

Foraging activity is concentrated within a small radius of the roost. Bumblebee bats have been observed feeding within about a kilometer of their caves, and often much closer. They tend to work the canopy and understory of vegetation lining riverbanks and clearings rather than flying high above the tree line. This low, close-to-vegetation foraging style aligns with their gleaning habits and their echolocation calls, which are tuned for short-range, cluttered environments.

The Metabolic Cost of Being Tiny

A two-gram mammal faces enormous metabolic demands relative to its body size. Smaller animals have higher surface-area-to-volume ratios, which means they lose body heat faster and burn through energy more quickly. For the bumblebee bat, this translates into a constant pressure to eat enough each night to avoid running an energy deficit.

Research on bat energetics, though conducted primarily on fruit-eating species rather than insectivores, illustrates how expensive it is to be a small bat. In studies of two frugivorous bat species, maintenance energy costs ran between roughly 3.6 and 5.4 times their basal metabolic rate, and those bats weighed considerably more than the bumblebee bat.¹ The same research found evidence that fruit bats are “energy maximizers,” ingesting more calories than they strictly need and regulating storage by adjusting metabolic output. Whether insectivorous bats like the bumblebee bat follow a similar strategy is less clear, but the principle that small bats have outsized energy needs holds across families.

The bumblebee bat has one key adaptation for managing its energy budget: torpor. Like many small bats, it can lower its body temperature and metabolic rate during the day while roosting, effectively putting its body in standby mode to conserve calories between foraging bouts. Torpor is especially important during cooler months or periods when insect availability drops. Without it, the bat’s resting metabolism alone could drain its energy reserves before the next evening’s feeding window opened.

This metabolic tightrope helps explain why the bumblebee bat’s habitat requirements are so specific. It cannot afford to roost far from productive foraging areas, and it cannot afford to live somewhere insects are scarce or unpredictable. Limestone caves near rivers in tropical forest are not an arbitrary preference. They are a metabolic necessity.

Seasonal Variation in Prey Availability

Thailand’s climate has distinct wet and dry seasons, and insect communities shift accordingly. During the wet season, insect abundance and diversity near waterways tends to spike. The warm, humid conditions promote hatching and emergence of many fly and beetle species, which means more food is available for insectivorous bats. During the dry season, insect populations can drop, and the mix of available species changes.

For the bumblebee bat, this likely means its diet composition varies across the year even if the broad categories stay the same. In months when midges and gnats are abundant, these soft-bodied flies may dominate. During drier stretches, the bat may rely more heavily on gleaned prey like bark lice and spiders, which are less dependent on standing water for their life cycles. This kind of seasonal flexibility is common among small insectivorous bats in tropical and subtropical regions, and the bumblebee bat’s dual foraging strategy of hawking and gleaning positions it to exploit whatever is available.

No one has conducted detailed month-by-month diet tracking of the bumblebee bat across a full year, so the specifics of seasonal dietary shifts remain inferred from habitat ecology and the behavior of related species rather than direct observation. This is a recurring theme in bumblebee bat research: the animal is rare, tiny, and lives in relatively inaccessible cave systems, which makes sustained field study difficult.

Pesticide Exposure and the Food Chain

Because the bumblebee bat depends entirely on insects and spiders, anything that reduces or contaminates its prey base is a direct threat to its survival. Pesticide use in and around the bat’s range is one such concern. Agricultural chemicals applied to crops near rivers can kill or reduce the insect populations the bat feeds on, and they can also accumulate in the insects themselves, meaning bats ingest toxins along with their meals.

Research on pesticide toxicity in insectivorous bats has shown that exposure can be harmful at surprisingly low doses. In studies on Indiana bats, a North American insectivorous species of similar size class, the pesticide permethrin caused impaired flight at doses as low as 16 percent of the lethal dose, meaning the bat did not have to consume anywhere near a fatal amount before its ability to hunt was compromised.² A bat that cannot fly properly cannot catch aerial prey, creating a vicious cycle where sublethal pesticide exposure leads to starvation even if the direct toxic dose was not fatal.

The same research highlighted that the form in which a pesticide is delivered matters enormously. The formulated commercial product of permethrin was roughly 13 times more toxic than the pure active ingredient alone, which suggests that real-world agricultural spraying poses a greater risk to bats than laboratory studies using purified chemicals might indicate.² Current pesticide risk assessments in many jurisdictions do not specifically account for bats, instead relying on toxicity data from rodents and birds as proxies. Given that bats have different metabolic rates, body compositions, and exposure patterns than these proxy species, the actual risk to insectivorous bats is likely underestimated.

Habitat Loss and Its Effect on Diet

The bumblebee bat’s highly specific habitat requirements make it vulnerable to deforestation and land-use change. Its entire known range spans a handful of limestone cave systems in western Thailand and parts of Myanmar. When the forest surrounding these caves is cleared for agriculture or development, the insect communities the bat relies on decline, fragment, or shift in composition. Even if the caves themselves remain intact, a bat that emerges into a landscape stripped of its foraging vegetation has nowhere productive to hunt.

River systems are particularly important. The waterways running through bumblebee bat habitat support the aquatic and semi-aquatic insect larvae that later become the flying adults the bats eat. Dam construction, water diversion, and pollution can all alter these insect communities. A river that once supported dense hatches of midges and gnats may produce far fewer if its flow regime changes or its water quality degrades.

Tourism is another pressure. Several of the caves where bumblebee bats roost have attracted visitors curious about the world’s smallest bat. Disturbance at roost sites can cause bats to abandon caves or to use energy flying around in response to intruders, energy they cannot easily replace given their already tight metabolic margins. Some caves in Thailand have been placed under protection, with restricted access, but enforcement varies and the bat’s range in Myanmar is less well monitored.

How the Bumblebee Bat Compares to Other Tiny Insectivores

The bumblebee bat is not the only small insectivorous bat, and comparing its diet and foraging ecology to related species helps put its lifestyle in context. Many vespertilionid bats in the two-to-ten-gram range eat similar prey: small flies, beetles, moths, and spiders. What makes the bumblebee bat unusual is not what it eats so much as the constraints under which it eats.

Most small insectivorous bats forage for longer stretches each night. Pipistrelles, for instance, may hunt for several hours with rest breaks in between. The bumblebee bat’s extremely brief foraging bouts of around 20 to 30 minutes each are unusually compressed. This may reflect a combination of its tiny energy reserves, which cannot sustain prolonged flight, and its proximity to prey-rich habitat, which allows it to fill up quickly.

The bumblebee bat also occupies an unusual taxonomic position. It is the sole member of its family, Craseonycteridae, which means it has no close living relatives for easy dietary comparison. Its closest evolutionary neighbors are distantly related, making it difficult to trace how its specific foraging niche and prey preferences evolved. In this sense, the bumblebee bat is a dietary island: an insectivore whose habits we understand in broad strokes but whose fine-grained ecology, including prey preferences at the species level, seasonal dietary budgets, and competitive interactions with other cave-roosting bats in its range, remains full of gaps.

Why So Little Is Known

The bumblebee bat was not described by science until 1974, when Thai zoologist Kitti Thonglongya collected specimens from a cave in Kanchanaburi Province. In the decades since, research has been sporadic. The bat’s tiny size makes it difficult to tag or track with conventional telemetry equipment. Its cave roosts are remote. Population estimates are uncertain, with most guesses ranging from a few thousand to perhaps tens of thousands of individuals across all known sites.

Dietary studies in particular require either capturing bats and analyzing their fecal pellets or using molecular techniques like DNA metabarcoding to identify prey from droppings collected in roosts. Both approaches have been applied to other small bat species with success, but the bumblebee bat’s rarity and the sensitivity of its roost sites have limited how much sampling researchers can do without risking disturbance. The result is that our picture of the bat’s diet comes from a relatively small number of observations, supplemented by reasonable inference from its habitat, jaw morphology, and the ecology of its known foraging areas.

This uncertainty is worth keeping in mind whenever you read definitive-sounding statements about what the bumblebee bat eats. The broad answer, small insects and spiders, is solid. The details, which insect species dominate in which season, how much the bat eats per night, whether it selects certain prey or takes whatever it encounters, are still largely open questions waiting for more fieldwork.