What Does a Nautilus Eat? Inside Its Unique Diet

Nautiluses are primarily scavengers that feed on crustacean molts, dead fish, and other organic debris drifting along deep reef slopes in the Indo-Pacific. They occasionally grab live prey like small shrimp and hermit crabs, but their reputation as ancient ocean predators far outstrips their actual hunting ability. What makes their diet genuinely interesting is not the menu itself but how they find, process, and extract energy from food in the deep, dark waters they inhabit, and how their feeding habits differ from virtually every other cephalopod alive today.

Scavenger First, Predator Second

Unlike their fast-moving cephalopod relatives, nautiluses are slow, buoyant drifters that lack the speed and precision to chase down agile prey. Their primary food sources are the shed exoskeletons and carcasses of crustaceans, particularly lobsters, crabs, and shrimp, along with occasional fish remains. They feed on carrion found on or near the bottom, typically at depths between about 150 and 700 meters, where the animals spend much of their time cruising along steep reef slopes.

Whether nautiluses lean more toward scavenging or active predation appears to depend on circumstances like population density and resource availability. Research on a Palauan population of Nautilus belauensis suggests that when food is abundant, nautiluses can shift toward more active foraging, expending more energy to seek out higher-value prey. In contrast, populations with fewer individuals and scarcer resources appear to rely heavily on strict scavenging to conserve energy.¹ This flexibility matters because, as you’ll see, the nautilus’s entire physiology is geared toward getting by on very little.

Finding Food in the Dark

Nautiluses hunt (or more accurately, scavenge) in deep, dimly lit waters where vision is of limited use. Their eyes are famously primitive by cephalopod standards: simple pinhole cameras with no lens, producing blurry images at best. So how do they find a crab carcass sitting on the reef floor hundreds of meters down? The answer is chemical detection, executed through a sophisticated array of tentacles.

A nautilus has roughly 90 tentacles, far more than any other living cephalopod, and these are not all doing the same job. Research on the tentacle and rhinophore epithelium of Nautilus pompilius has identified two functionally distinct tentacle types. Lateral slender digital tentacles, including the elongated lowermost pair, are equipped with sensory cells suited for long-distance chemoreception, essentially smelling food from a distance through the water. Medial digital tentacles, on the other hand, have terminal nerve structures that appear specialized for contact chemoreception, meaning they identify food by touching it.²

In practice, this means a nautilus drifting through the water column picks up chemical cues from decaying tissue or crustacean molts well before reaching the source. It adjusts its course accordingly, then uses its shorter contact tentacles to assess the food up close before pulling it toward its beak. This two-stage chemosensory system is one reason nautiluses can thrive as scavengers despite being slow swimmers with poor eyesight.

How the Digestive Tract Handles a Meal

Once a nautilus gets food to its beak, it tears it into pieces using a powerful, parrot-like jaw and a radula, a ribbon of tiny teeth common to most mollusks. From there, the food enters a digestive system that has been studied using X-ray imaging and computed tomography on living animals, giving a detailed picture of what happens inside.

Within about 20 minutes of eating, food reaches the stomach, where it is broken into small pieces. Most of the material then passes into the crop, a storage organ that can balloon to roughly four times its resting size to accommodate a large meal. The chyme (partially digested food) reaches the midgut gland after about three hours and enters the rectal loop by five hours. The entire process from eating to elimination takes around 12 hours.³ That’s remarkably slow compared to many fish or squid, reflecting the nautilus’s low metabolic rate and its habit of eating large, infrequent meals rather than foraging constantly.

The digestive organs themselves are equipped with a range of enzymes, including trypsin-like and chymotrypsin-like enzymes in the gut lining, which break down protein. The caecum, a pouch in the digestive tract, contains endosymbiotic bacteria, microorganisms living within the gut cells that likely assist with digestion.⁴ Endosymbiotic bacteria in gut tissue are not unique to nautiluses, but their presence highlights that these animals rely on microbial help to extract nutrition from what is often tough, protein-rich carrion.

A Diet That Changes Over a Lifetime

One of the more surprising findings about nautilus feeding comes from stable isotope analysis, a technique where researchers measure the ratio of different nitrogen isotopes in shell material to infer what an animal was eating at various points in its life. In most cephalopods, nitrogen isotope values increase as the animal grows, reflecting a climb up the food chain: young animals eat small things, and older animals eat bigger, higher-level prey. Nautiluses do the opposite.

Analysis of Nautilus pompilius and Allonautilus scrobiculatus shells reveals a gradual decline in nitrogen isotope values across successive growth stages, suggesting that as nautiluses age, they either feed at a lower position in the food web or shift toward food sources with lower nitrogen signatures.⁵ This pattern contrasts sharply with squid and cuttlefish, which show the more typical cephalopod trajectory of increasing trophic level with size.

The life-history picture that emerges is roughly three stages. During embryonic development, the animal subsists on yolk, which carries relatively high nitrogen isotope values. After hatching, there is a noticeable drop, reflecting the switch from yolk to external food. In the juvenile-through-adult phase, values stabilize at a lower range, consistent with a steady scavenging diet. This declining pattern makes sense if adult nautiluses increasingly rely on carrion and crustacean molts, items that are abundant but not as isotopically “rich” as the live prey a young, growing animal might consume. The same declining isotope pattern also appears in the vampire squid, another deep-water cephalopod known for eating “marine snow” and detrital material, hinting at a broader link between deep-water scavenging lifestyles and this unusual trophic trajectory.⁵

Built for Fasting

Nautiluses do not need to eat very often. Their metabolic rate is remarkably low for a cephalopod, and this shapes everything about their relationship with food. While a squid burns energy at a furious rate and needs to eat frequently to stay alive, a nautilus can go weeks between meals. Captive nautiluses have been documented surviving extended fasts without obvious distress, and their wild behavior reflects a creature that is in no rush.

This metabolic thriftiness becomes even more extreme in low-oxygen conditions. When nautiluses encounter progressive hypoxia, a common situation in the deep waters they inhabit, they respond by suppressing their aerobic metabolic rate to roughly 5 to 10 percent of what it would be while resting in well-oxygenated water. Activity drops to near zero, punctuated by occasional brief bursts of jet propulsion.⁶ This ability to throttle down so dramatically means the nautilus can survive in environments where food is scarce and conditions are harsh, rather than needing to stay in productive, well-oxygenated zones where competition is fierce.

Separate research on free-swimming Nautilus pompilius confirms that this tolerance isn’t just a laboratory curiosity. In the wild, nautiluses regularly enter waters with low dissolved oxygen levels, and their large internal oxygen stores combined with metabolic suppression enable them to forage or transit through these zones without being forced back to shallower, better-oxygenated water.⁷ From a dietary perspective, this is significant. It means nautiluses can access food sources in low-oxygen zones that many competitors and predators cannot reach.

What Heavy Metal Levels Reveal About the Diet

Because nautiluses spend their lives on and near the sea floor eating carrion and crustaceans, they accumulate trace metals in their tissues at concentrations that tell researchers something about what the animals encounter in their environment. A study of Nautilus macromphalus from New Caledonia found high levels of multiple trace elements, sometimes comparable to those found in shellfish from contaminated coastal areas, even though these nautiluses inhabit relatively remote deep-water habitats. The digestive gland, the main organ responsible for processing food, concentrated cadmium, cobalt, iron, vanadium, and zinc, while the excretory tissues (renal and pericardial appendages) accumulated silver, aluminum, arsenic, chromium, and nickel. Elevated nickel and chromium in the hemolymph, the nautilus’s blood equivalent, suggested particularly high environmental exposure to those metals.⁸

A comparative study between Nautilus pompilius from Vanuatu and Nautilus macromphalus from New Caledonia confirmed the digestive gland as the key organ for accumulating and storing metals like silver, cadmium, copper, and iron, while excretory tissues handled arsenic, chromium, manganese, lead, and selenium.⁹ The pattern held across both species and both locations, which suggests it reflects something fundamental about the nautilus digestive system rather than a quirk of local water chemistry.

For researchers, these trace metal profiles serve as indirect dietary records. The elements a nautilus accumulates mirror what it eats, and its scavenging lifestyle exposes it to a broader range of metals than you would see in a pelagic predator that eats only fresh prey. The digestive gland, which processes every meal, becomes a kind of chemical archive of the animal’s feeding history.

How Nautiluses Compare to Their Ancient Relatives

Nautiluses are often called “living fossils,” a label that can be misleading but captures something real: they are the last surviving members of a lineage that once included thousands of shelled cephalopod species. Their closest ancient relatives, the ammonites, went extinct alongside the non-avian dinosaurs about 66 million years ago. Ammonites looked superficially similar to nautiluses, with coiled external shells, but their diets were probably quite different.

A study of exceptionally preserved ammonite jaws found alongside food remains suggested that at least some ammonite groups fed on plankton rather than scavenging on the sea floor. The jaw morphology was consistent with planktivory, and the researchers proposed that this diet may have been widespread among a major ammonite subgroup that shared the same jaw structure.¹⁰ If so, ammonites and nautiloids occupied very different feeding niches despite their superficial resemblance: ammonites filtering plankton in the water column, nautiluses scavenging on the bottom.

This distinction has practical evolutionary implications. Planktivorous ammonites would have been far more vulnerable to the kind of food-web collapse that followed the asteroid impact at the end of the Cretaceous, when plankton communities were devastated. Nautiluses, eating dead material and crustacean scraps on the deep reef slope, would have been more insulated from that catastrophe. Their scavenging diet, flexible and undemanding, may be one reason the lineage survived when so many shelled cephalopods did not.

Why Nautiluses Are Hard to Study in the Wild

Much of what we know about nautilus diet comes from captive feeding studies and occasional trap observations rather than comprehensive field data. These animals live at depths that make direct observation difficult, and they do not take well to surface pressure. Their shell, which provides buoyancy in deep water, imposes a hard depth limit in the other direction: nautiluses cannot survive above about 800 meters of depth pressure, meaning they are confined to a band between roughly 100 and 700 meters in most habitats. Researchers studying their feeding behavior typically use baited traps lowered to known nautilus depths, then infer diet from what attracts the animals and from gut content analysis of captured specimens.

Captive nautiluses eat readily, accepting pieces of fish, shrimp, and crab. Aquariums have maintained Nautilus pompilius for years on diets of fresh and frozen seafood, and captive animals have contributed substantially to our understanding of digestive timing and nutrient processing. But aquarium diets are richer and more predictable than anything a wild nautilus encounters, and isotope studies on captive shells have confirmed that switching from a natural to an artificial diet produces a measurable shift in the chemical signature of new shell growth. In other words, captive feeding studies tell us what a nautilus can eat and how it processes food, but they are only a rough guide to the variety, frequency, and quality of food a wild animal actually encounters.

The combination of deep habitat, slow reproduction, and patchy distribution means that basic questions about nautilus diet remain partially open. Researchers still debate how much live prey nautiluses actually capture versus how much of their intake is true scavenging. Seasonal variation in diet, differences between juveniles and adults in the wild, and the importance of specific prey species are all areas where data remains thin. For a creature that has persisted for hundreds of millions of years, the nautilus has been remarkably reluctant to let scientists watch it eat.