Tardigrades eat algae, moss cells, bacteria, fungi, and in some cases other tiny animals like nematodes and rotifers. The specific diet depends heavily on the species. Some tardigrades are strict herbivores that pierce plant cells and suck out the contents, others are confirmed carnivores that can only reproduce when fed animal prey, and still others are true omnivores that happily consume both plants and microscopic animals. The range is wider than most people expect from a creature barely visible to the naked eye.
How Tardigrades Actually Eat
Tardigrades do not chew. They pierce and suck. Their feeding apparatus is a complex structure centered on a pair of sharp stylets, essentially tiny daggers housed inside protective sheaths called stylet coats. These stylets connect to a muscular sucking pharynx that works like a pump. When a tardigrade finds a food source, it pushes its stylets into a cell wall, an algal body, or even the skin of another animal, and then uses pharyngeal suction to draw the contents into its gut.1Journal of Limnology. Comparative analysis of the tardigrade feeding apparatus: adaptive convergence and evolutionary pattern of the piercing stylet system
The whole apparatus is reinforced with calcium carbonate in the crystalline form of aragonite, the same mineral found in seashells and coral. The piercing stylets appear to be made almost entirely of aragonite, which makes them rigid enough to puncture tough cell walls.2Oxford Academic (Integrative and Comparative Biology). Distribution of Calcium and Chitin in the Tardigrade Feeding Apparatus in Relation to its Function and Morphology This mineralization is part of why tardigrades can exploit such a wide range of food sources. A cell wall that would be impenetrable to a soft mouthpart becomes accessible when you have crystalline daggers and a vacuum pump.
Tardigrades shed and regrow their stylets each time they molt, which happens several times over their lifespan. The old stylets are left behind in the shed cuticle, and fresh ones form quickly. This regular replacement means the tools stay sharp throughout the animal’s life.
The Plant Eaters
A large proportion of tardigrade species are herbivores. Their primary food sources are algae, moss cells, and cyanobacteria. Researchers who spent months carefully watching heterotardigrades in the genera Echiniscus, Pseudechiniscus, and Viridiscus found that these animals feed on two main things: the chloroplasts and cytoplasm from moss cells, particularly moss protonema (the threadlike early growth stage of moss), and single-celled green algae associated with the moss, typically Chlorella vulgaris.3Invertebrate Biology. How to culture limnoterrestrial heterotardigrades
This feeding strategy explains why tardigrades are so commonly found in moss cushions and lichen patches. These environments are not just humid shelters. They are grocery stores. The thin films of water that moss retains create the perfect habitat for a creature that needs both moisture and a steady supply of photosynthetic cells to puncture and drain. When you find a clump of moss on a wall or a roof, you are looking at a tardigrade buffet.
Lab experiments have confirmed that the well-studied species Hypsibius exemplaris is a herbivore that feeds on cyanobacteria, algae, and fungi.4Zoological Journal of the Linnean Society. Dietary preferences and diet effects on life-history traits of tardigrades Fungi might seem surprising in a discussion of “plant eaters,” but many tardigrades classified as herbivores or microbivores are really just piercing whatever stationary cells they come across. The distinction between eating an algal cell and eating a fungal hypha is less about preference and more about what is available and puncturable.
The Hunters
Some tardigrades eat other animals, and they are surprisingly active predators for creatures that top out at about half a millimeter long. The genus Milnesium is the most famous example. Milnesium inceptum can only reproduce successfully when fed animal prey. In controlled experiments, it failed to sustain a population on plant-based diets alone.4Zoological Journal of the Linnean Society. Dietary preferences and diet effects on life-history traits of tardigrades Milnesium tardigradum, a related species, has been successfully reared in the lab on a diet of rotifers, which are tiny multicellular animals found in the same wet habitats tardigrades occupy.5Zoological Science. Life History of Milnesium tardigradum Doyère (Tardigrada) under a Rearing Environment
When given a choice between nematodes, rotifers, and other tardigrades as prey, predatory tardigrades generally prefer nematodes and tend to avoid eating fellow tardigrades.6Applied Soil Ecology. Buccal tube dimensions and prey preferences in predatory tardigrades This avoidance of cannibalism is interesting from an ecological standpoint. Tardigrades and nematodes often share the same microhabitats in moss and soil, and nematodes are typically softer-bodied and easier to subdue. It likely has practical benefits: eating your neighbors of the same phylum risks picking up shared parasites or simply losing the fight, since other tardigrades have the same armored cuticle and stylet weaponry you do.
The size of a predatory tardigrade’s buccal tube, the internal channel through which food passes, appears to constrain what it can eat. Researchers have explored whether buccal tube dimensions predict prey preference, since an animal has to physically fit its meal through this opening. Larger-bodied predatory tardigrades with wider buccal tubes have access to bigger prey items, which is one way that different predatory species partition the same habitat without competing directly for the same food.6Applied Soil Ecology. Buccal tube dimensions and prey preferences in predatory tardigrades
Omnivores and the Flexibility Advantage
Between the strict herbivores and the committed carnivores sits a third group: omnivores. Paramacrobiotus fairbanksi, for example, feeds on cyanobacteria, algae, fungi, and animals. It thrives on a mixed diet in ways that obligate herbivores and carnivores cannot match.4Zoological Journal of the Linnean Society. Dietary preferences and diet effects on life-history traits of tardigrades This flexibility likely gives omnivorous species an edge in unpredictable environments. If algae dry up, they can switch to hunting. If animal prey is scarce, they can graze.
Field surveys in boreal peatlands support the idea that omnivores dominate many natural tardigrade communities. In a study of moss-dwelling tardigrades across Finnish peatlands, omnivores were the most common trophic group in most habitats. Carnivorous tardigrades from the family Milnesiidae appeared only in more densely forested peatlands and even there represented only about two to five percent of the tardigrade population.7PubMed Central. A first look into moss living tardigrades in boreal peatlands In more open peatlands with fewer trees, herbivorous and microbivorous tardigrades were either equal to or slightly outnumbered omnivores.
This pattern mirrors what ecologists see in larger food webs: top predators are always rarer than the organisms below them, because energy is lost at every step up the chain. A moss cushion can support many algae-eating tardigrades but only a handful of tardigrade-eating tardigrades. The pyramid holds even at this microscopic scale.
Surviving Without Food
Tardigrades are famous for surviving extreme conditions by entering a dried-out dormant state called anhydrobiosis. When their environment dries out, they curl into a compact form known as a tun, losing almost all their body water. In this state they do not eat, move, or metabolize in any detectable way. But survival during dormancy is not free. The energy to endure it and to wake up afterward comes from reserves built up during active feeding.
Storage cells within a tardigrade’s body accumulate lipid droplets during periods of active feeding. These lipid reserves may serve as the energy source that fuels the biochemical preparations a tardigrade makes when entering anhydrobiosis, and they likely power the metabolic restart after rehydration as well.8PLOS ONE. A comparative ultrastructure study of storage cells in the eutardigrade Richtersius coronifer in the hydrated state and after desiccation and heating stress In other words, the quality of a tardigrade’s feeding before dormancy directly affects its chances of surviving that dormancy. A well-fed tardigrade enters the tun state with a better safety margin than a starved one.
Recovery from anhydrobiosis is also tied to the duration of dormancy. The longer a tardigrade stays in the tun state, the more time it needs to return to activity after rehydration. After short dormancy periods of up to about 60 days, tardigrades resume coordinated crawling fairly quickly. After 120 days, the wake-up period stretches noticeably, and after 240 days it is longer still.9PLOS ONE. How long can tardigrades survive in the anhydrobiotic state? A search for tardigrade anhydrobiosis patterns Age also matters: younger tardigrades recover more reliably, and individuals that emerge from dormancy in groups fare better than those that come back alone.10PubMed Central. Recovery from anhydrobiosis in the tardigrade Paramacrobiotus experimentalis: Better to be young than old and in a group than alone One plausible reason for the group advantage is that multiple rehydrating tardigrades disturb the water around them, potentially signaling or mechanically stimulating their neighbors into waking up. But the underlying point is that feeding history, dormancy length, and recovery are all linked. A tardigrade that fed well before going dormant and did not stay dried out too long has the best shot at resuming its life and its diet afterward.
How Diet Shapes the Gut
The tardigrade digestive tract is simple compared to a vertebrate’s, essentially a tube running from the pharynx to the anus. But the details of that tube vary with diet. Ultrastructural studies of the midgut, the main digestive region, show clear differences between species that eat plants and species that eat animals. The thickness of the intestinal wall, the folding patterns on both the inner and outer surfaces of the gut lining, and the intensity of absorptive structures all vary depending on whether a species is phytophagous or zoophagous.11Journal of Limnology. Comparative midgut ultrastructure in three species of Tardigrada This makes intuitive sense. Breaking down a mouthful of algal cytoplasm is a biochemically different task from digesting animal protein, and the gut adapts accordingly.
These differences also appear to track with habitat. Tardigrades from marine, freshwater, and terrestrial environments show distinct gut morphologies, and species capable of anhydrobiosis have gut features that differ from species that stay hydrated year-round.11Journal of Limnology. Comparative midgut ultrastructure in three species of Tardigrada The gut of a tardigrade that regularly dries out and rehydrates has to withstand repeated cycles of extreme physical stress, and its structure reflects that.
Their Gut Microbiome
Like most animals, tardigrades host communities of bacteria in their guts. Research on Antarctic stream-dwelling tardigrades found that the microbial communities inside tardigrades were clearly distinct from those in the surrounding microbial mats where the tardigrades lived and fed. The single most important factor determining what bacteria lived inside a tardigrade was the identity of the host species, more than the type of mat or the specific stream location.12Scientific Reports. Host identity is the dominant factor in the assembly of nematode and tardigrade gut microbiomes in Antarctic Dry Valley streams In other words, two tardigrades of the same species living in different streams had more similar gut bacteria than two different species living in the same stream.
This finding suggests that tardigrades are not just passively acquiring whatever bacteria are in their food. Something about each species’ gut environment, likely a combination of pH, immune factors, and digestion chemistry, actively selects for particular microbial communities. The functional profiles of these microbiomes also differed by host species, meaning different tardigrade species likely get different biochemical contributions from their gut bacteria.12Scientific Reports. Host identity is the dominant factor in the assembly of nematode and tardigrade gut microbiomes in Antarctic Dry Valley streams Researchers are still working out what those contributions are, but in other invertebrates gut bacteria help with everything from nutrient extraction to pathogen defense.
Feeding Tardigrades in the Lab
If you want to keep tardigrades alive in a research setting, or even as an unusual hobby, feeding is one of the trickiest parts. Different species need different diets, and getting it wrong means the population declines. For herbivorous species, researchers typically culture algae like Chlorella in the same dish or provide cyanobacterial cultures. For the carnivorous Milnesium tardigradum, the established method involves keeping thin agar plates in small dishes with water, introducing the tardigrades, and adding rotifers as food. The water needs to be changed at each feeding, and the animals should be checked daily. Feeding every three days can sustain the animals, but a restricted feeding schedule reduces the number of eggs per clutch, meaning reproduction suffers even if survival does not.5Zoological Science. Life History of Milnesium tardigradum Doyère (Tardigrada) under a Rearing Environment
Culturing heterotardigrades, which are generally harder to maintain than eutardigrades in lab conditions, requires providing both moss protonema and associated algae. Researchers who successfully maintained Echiniscus and related genera found that simply supplying the right moss species and its natural algal companion was enough, but it took extended observation to figure out what “the right moss” even was.3Invertebrate Biology. How to culture limnoterrestrial heterotardigrades Many tardigrade species have never been successfully cultured at all, in part because their dietary requirements remain unknown.
Microplastics and Accidental Ingestion
Given that tardigrades feed by piercing and sucking rather than filter-feeding or gulping, you might wonder whether they accidentally consume microplastic particles the way many aquatic organisms do. The limited research so far suggests they largely do not. Field studies in semi-aquatic environments found no uptake of microplastic fibers by tardigrades, though comprehensive data from terrestrial soils are still lacking.13Copernicus Publications. What do we know about how the terrestrial multicellular soil fauna reacts to microplastic?
This makes some mechanical sense. Tardigrades are not indiscriminate feeders. They target specific cells or organisms, insert their stylets, and extract liquid contents. A stray microplastic fiber sitting on a moss leaf would not trigger the feeding behavior the way a plump algal cell would. That said, this is an area where the data are thin. If microplastic particles were small enough and happened to be embedded in a food organism, it is not clear whether a tardigrade’s feeding apparatus would reject them. Given that tardigrades are widespread in soils and mosses worldwide, understanding their exposure to contaminants has real ecological relevance, even if researchers have not yet caught them swallowing plastic.