Parasites are eaten by a surprisingly wide range of organisms, from tiny bacteria that invade and kill parasitic microbes to birds that spend their entire day picking ticks off large mammals. Some of these parasite-eaters are wild animals following natural instincts, others are deliberately deployed by farmers and aquaculture operations, and a few are even parasites themselves that prey on other parasites.
Cleaner Fish on Coral Reefs
The cleaner wrasse is one of the most prolific parasite predators in nature. These small reef fish set up “cleaning stations” where larger fish line up to have parasites removed from their skin, gills, and mouths. A single cleaner wrasse eats more than 1,200 parasites per day, feeding mainly on tiny crustaceans called gnathiid isopods that attach to fish and feed on their blood. The wrasse also consume parasitic flatworms. Their diet occasionally includes a bit of client mucus (the protective slime coating fish skin), which the wrasse actually prefer as a snack, but the parasites are a steady staple.
This cleaning relationship is so important to reef ecosystems that when researchers have removed cleaner wrasses from experimental reef patches, parasite loads on surrounding fish increase dramatically and some fish species leave the area entirely.
Lumpfish and Wrasse in Salmon Farming
The same principle works at industrial scale. Sea lice are a major parasite problem on salmon farms, costing the aquaculture industry billions annually. Rather than relying solely on chemical treatments, many farms now stock their pens with lumpfish or ballan wrasse that eat lice directly off the salmon.
The results can be striking. In experimental sea pens, lumpfish reduced adult female sea lice by 93 to 97% compared to pens without them. In larger commercial-scale trials, lice reductions ranged from 60 to 100% during certain periods, depending on the ratio of lumpfish to salmon and the time of year. Importantly, the presence of cleaner fish doesn’t affect salmon growth, making this a practical alternative to repeated chemical delousing.
Oxpeckers and Tick Control
Red-billed oxpeckers are the classic example of a land animal that specializes in eating parasites. These African birds perch on cattle, buffalo, giraffes, and other large mammals, systematically picking through fur and skin for ticks. Stomach analyses of 53 red-billed oxpeckers found a total of 21,641 ticks, with individual birds carrying anywhere from 16 to 1,665 ticks in a single stomach. Tick larvae made up 38% of the count, and about half of all ticks consumed belonged to a genus that’s one of the most economically damaging cattle parasites in Africa.
Nestling oxpeckers also get fed parasites: about 46% of their diet consists of ticks, with the rest being flies, hair, and tissue. The birds do eat some blood and skin from their hosts too, which has led to debate about whether they’re truly helpful or partly parasitic themselves. But the sheer volume of ticks they remove suggests a net benefit for most host animals.
Primates That Groom Away Lice
Social grooming in monkeys and apes isn’t just about bonding. In Japanese macaques, researchers confiscated what the monkeys picked up during grooming sessions and found that the vast majority of items were parasites. Specifically, 98.9% of what macaques picked off each other and ate were louse eggs. They also removed adult lice from two species that infest their fur. Grooming is often framed as a social behavior, but the data strongly supports parasite removal as its primary practical function.
Mosquitofish and Parasite Vectors
Some animals don’t eat parasites directly but devour the insects that carry them. Mosquitofish are a well-known example. A single adult mosquitofish can eat up to 100 mosquito larvae per day. Since mosquitoes transmit malaria, dengue, West Nile virus, and several parasitic worms, reducing mosquito populations has a direct impact on parasite transmission. Mosquitofish have been introduced to freshwater systems around the world specifically for this purpose, though their aggressive nature can disrupt native ecosystems.
Predatory Mites in Poultry Houses
Poultry red mite is one of the most damaging parasites in egg production, infesting laying hens and reducing both bird health and egg output. Several species of predatory mites naturally occur in poultry houses and feed on red mites. These include species in the genera Hypoaspis, Androlaelaps, and Stratiolaelaps, all of which prey on red mites and their eggs.
These predators aren’t exclusive red mite specialists, which limits their long-term effectiveness when used alone. But in enclosed environments like poultry barns, they can meaningfully suppress mite populations as part of a broader pest management strategy. A small beetle called Carcinops pumilio, which lives in poultry manure, is also encouraged by producers because it feeds on mite eggs and larvae.
Fungi That Trap Parasitic Worms
Some of the most unusual parasite predators are soil fungi that physically trap and consume parasitic nematodes (roundworms). These nematode-trapping fungi produce sticky loops, constricting rings, or adhesive nets along their filaments. When a parasitic worm larva crawls through the soil, it gets caught, and the fungus slowly digests it.
Most research has focused on a species called Arthrobotrys oligospora, but more recent studies have identified other fungal species that are even more efficient at trapping infective larvae in livestock feces. Some of these fungi can even survive passage through the digestive tract of cattle and sheep, meaning farmers could potentially feed them to livestock as a living dewormer. This approach hasn’t become standard practice yet, but it represents a biological alternative to chemical dewormers, which are losing effectiveness as parasites develop resistance.
Bacteria That Hunt Other Bacteria
At the microscopic level, a predatory bacterium called Bdellovibrio bacteriovorus attacks and kills other bacteria by physically invading them. It latches onto a target cell, drills through the outer membrane, takes up residence inside, and consumes the host from within before bursting out as multiple new predator cells. Its prey includes several pathogenic species responsible for serious infections, including Klebsiella pneumoniae, Acinetobacter baumannii, and Serratia marcescens. In animal studies, treatment with this predatory bacterium even protected mice from a lethal dose of Yersinia pestis, the bacterium that causes plague.
Some prey bacteria have evolved defenses. One species produces cyanide that halts the predator’s growth once it enters the cell. This microscopic arms race mirrors the predator-prey dynamics seen in much larger organisms.
Parasites That Eat Other Parasites
Perhaps the most mind-bending category: hyperparasitoids, which are parasites of parasites. Certain tiny wasps lay their eggs inside the larvae of other parasitic wasps, which are themselves developing inside a caterpillar host. The process is layered. A primary parasitoid wasp injects its eggs into a caterpillar. A hyperparasitoid wasp then locates that caterpillar, pierces through both the caterpillar’s skin and the developing parasitoid larva inside, and deposits its own eggs. The hyperparasitoid larvae eventually consume and kill the primary parasitoid larvae, then use the leftover cocoon as their own pupation chamber.
One well-studied example involves a hyperparasitoid wasp called Baryscapus galactopus, which targets Cotesia glomerata, itself a parasitoid of cabbage butterfly caterpillars. These layered relationships can extend even further, with some ecosystems supporting parasites four or five levels deep.