Marmoset monkeys are gum eaters. In the wild, tree gum and sap make up the overwhelming majority of their diet, sometimes accounting for over 97% of their feeding activity. The rest comes from insects, fruit, and the occasional small animal. This heavy reliance on tree exudates sets marmosets apart from most other primates and shapes everything from their teeth to their gut bacteria.
Tree Gum: The Foundation of the Diet
Marmosets belong to a small group of primates that specialize in eating the sticky, carbohydrate-rich gum that oozes from tree bark. In the Atlantic Forest of northeastern Brazil, researchers tracking common marmosets found that gum made up 97% to 98% of all feeding bouts across three separate forest fragments. The marmosets targeted just two tree species in those areas, returning to the same individual trees day after day. Other wild populations favor gum from cashew trees and angico trees, whose gum has a chemical structure similar to the gum arabic you might recognize from food labels.
This isn’t passive foraging. Marmosets actively gouge holes into bark to trigger gum flow, then return later to harvest what’s seeped out. They have specialized lower teeth that are narrow, forward-angled, and lack thick enamel on the inner surface, essentially turning their mouth into a wood-chipping tool. No other primate group has this adaptation to the same degree. The gum itself is rich in complex sugars that most animals can’t digest efficiently, but marmosets have an enlarged section of their lower gut that ferments these sugars and extracts energy from them.
Gum consumption follows a daily rhythm. It peaks in the early morning, drops off during midday, then picks up again in the afternoon. This pattern likely reflects how quickly gum accumulates in the holes marmosets have previously gouged.
Insects, Lizards, and Other Protein Sources
While gum provides most of their calories, marmosets need animal protein too. They eat a range of insects, and they’ll also take small lizards, nesting birds, and bird eggs when the opportunity arises. In fragmented forests where food diversity is limited, insects and other animal prey may account for only 1% to 2% of feeding activity, but in richer habitats, the proportion can be higher.
Insect foraging has its own daily pattern. Marmosets hunt for bugs most intensively during the hottest hours of the day, when insects are more active and visible. During dry seasons, when fruit and other plant foods become scarce, marmosets roughly double their foraging time compared to wet seasons, spending about 21% of daylight hours searching for food versus around 10% during wetter months.
Fruit, Flowers, and Other Plant Foods
Despite being primates, marmosets eat surprisingly little fruit. In the Brazilian Atlantic Forest study, fruit accounted for less than 2% of feeding bouts. Flowers appeared even less frequently. This doesn’t mean marmosets avoid fruit entirely. In larger, more diverse forests with greater fruit availability, they eat more of it. But their ability to fall back on tree gum, a resource that’s available year-round and that few competitors can access, means they’re never dependent on seasonal fruit the way many other monkeys are.
This dietary flexibility is one reason common marmosets thrive in disturbed and fragmented habitats where other primates struggle. Even a small patch of forest with the right tree species can sustain a marmoset group.
How Marmosets Spend Their Day
Feeding and foraging together occupy a major chunk of a marmoset’s waking hours. Studies of Geoffroy’s marmosets found that the animals spent about 21% of daylight hours eating, 14% foraging for insects and other prey, and 13% gouging trees for gum. That adds up to nearly half the day devoted to food-related activity. The remaining time splits between resting (29%) and traveling between food sources (20%).
For an animal weighing only 300 to 400 grams (roughly the weight of a can of soda), the daily caloric requirement is modest by human standards: about 42 to 48 calories per day. But relative to body size, that’s a high metabolic demand, which explains why marmosets spend so much time securing food.
Vitamin D: A Unique Nutritional Need
Marmosets have an unusual relationship with vitamin D that matters enormously for anyone keeping them in captivity. They require up to four times more vitamin D3 than other New World primates. Without enough of it, they develop metabolic bone disease, a painful condition where bones soften and fracture. Wild marmosets likely get adequate vitamin D3 from a combination of sun exposure and diet, with healthy wild populations showing blood levels averaging around 62 nanograms per milliliter. Captive marmosets diagnosed with bone disease typically have levels below 20.
Complicating things further, marmosets and other New World primates process plant-based vitamin D2 poorly. They specifically need vitamin D3 (cholecalciferol), the same form humans produce from sunlight. Without daily direct sun exposure, captive marmosets depend entirely on dietary sources. Commercial marmoset diets are formulated with high vitamin D3 levels to compensate, but those same diets can actually be toxic to other primate species, so they should never be shared across different types of monkeys.
Feeding Captive Marmosets
Captive marmoset diets typically combine a commercially formulated pellet with fresh fruits, vegetables, insects, and gum arabic as a substitute for wild tree gum. The pellet provides a nutritional baseline, particularly the high vitamin D3 levels these animals need, while fresh foods add variety and enrichment. Mealworms, crickets, and other feeder insects serve as the protein component, mimicking what marmosets would catch in the wild.
Getting the balance right is tricky. Marmosets in captivity often prefer sweet fruits over pellets, which can lead to nutritional gaps if caregivers don’t manage portions carefully. The recommended dietary vitamin D3 level for primate feed is 2,000 to 3,000 international units per kilogram of dry food, though the exact minimum needed to keep marmosets healthy remains an open question. Institutions that house marmosets report significant variation in how much vitamin D3 they provide, and the threshold where supplementation crosses into toxicity isn’t precisely established.
Offering gum arabic on branches or in puzzle feeders gives captive marmosets a chance to use their specialized teeth and practice the gouging behavior that defines their feeding ecology. This kind of behavioral enrichment is just as important as the nutritional content itself, since bored marmosets that can’t express natural foraging behaviors often develop stress-related health problems.