--- title: "Giant Isopod — The Deep Sea Roly-Poly That Survived 5 Years Without Food" url: https://thesea.org/giant-isopod/ date: 2026-02-25 modified: 2026-11-13 lang: en author: "Blane Perun" description: "The giant isopod is a deep-sea crustacean that can exceed 75 cm, survive years without food, and roll into an armored ball when threatened. Here is everything worth knowing about the ocean’s largest pill bug." categories: - "Bizarre Sea Creatures" image: https://thesea.org/wp-content/uploads/Bizarre-15-1024x572.jpg word_count: 2326 --- # Giant Isopod — The Deep Sea Roly-Poly That Survived 5 Years Without Food [TheSea.Org](/)▸[Deep Ocean](/bizarre-sea-creatures/)▸Giant Isopod # Giant Isopod — Bathynomus giganteus Deep Ocean By [Blane Perun](/about-blane-perun/) April 15, 2026 10 min read What is a giant isopod? The giant isopod (*Bathynomus giganteus*) is a deep-sea crustacean found at about 310–2,140 metres depth in the western Atlantic, from the southeastern United States and the Gulf of Mexico to Brazil. It is among the largest isopods in the world, typically 19–36 cm long with confirmed specimens to about 50 cm, and is essentially a massively scaled-up version of the pill bug or roly-poly you find under rocks in a garden. Both share the same isopod body plan; the deep-sea version simply took it to an extreme that took scientists by surprise when the species was first described in 1879. Quick facts Scientific name**Bathynomus giganteus** OrderIsopoda Depth range~310–2,140 m (mostly 365–730 m) Typical size19–36 cm Largest confirmed~50 cm (76 cm claim unverified) DietScavenger — whale falls, fish, debris Max fast recorded5+ years (Toba Aquarium, Japan) Conservation statusNot assessed (IUCN) Pull a giant isopod out of the deep sea and the reaction is almost always the same: immediate recognition followed by immediate disbelief. It looks exactly like a roly-poly bug — the same segmented body, the same dome of overlapping armored plates, the same ability to curl into a defensive ball — except it is the size of a football. Sometimes larger. The resemblance is not coincidental. Giant isopods and pill bugs are relatives, members of the same crustacean order. The deep sea simply took that body plan and ran with it. What is deep-sea gigantism? Giant isopods are one of the most frequently cited examples of deep-sea gigantism — the tendency of certain invertebrate groups to reach far larger body sizes in the deep ocean than their shallow-water relatives. The phenomenon is real and documented across multiple invertebrate groups. Cold water temperatures slow metabolic rates and may favour larger body size. The scarcity of food in the deep sea means larger body size provides reserves for surviving long periods without eating. What is clear is the result: while a typical garden pill bug is 1–2 cm, the giant isopod can reach around 50 cm. When French zoologist Alphonse Milne-Edwards described *Bathynomus giganteus* in 1879 from a juvenile male caught off the Dry Tortugas, it was a public sensation. Only a few years earlier, scientists had still argued that the deep ocean was lifeless. ~50 cmLargest confirmed length 2,140 mMaximum recorded depth 5+ yrsLongest documented fast ![Giant isopods scavenging a dead fish on the deep seafloor, a rare feast in the food-poor deep sea](https://thesea.org/wp-content/uploads/v2-giant-isopod-diet-and-the-feast-or-famine-deep-sea-thesea-org-by-blane-perun.webp)Giant isopods scavenging a dead fish on the deep seafloor, a rare feast in the food-poor deep sea Diet and the feast-or-famine deep sea The giant isopod’s feeding strategy is shaped entirely by the unpredictable and generally sparse food supply of the deep ocean floor. Giant isopods are primarily scavengers. On the abyssal and bathyal plain, food does not arrive on a schedule. A whale carcass sinks. A large fish dies and falls. These events are unpredictable and may be separated by months or years. Giant isopods are adapted to exploit them when they occur and survive the gaps between them. When food is available, they eat aggressively and to enormous excess — the body visibly swollen — loading energy reserves that may need to last a very long time. ! **The Toba Aquarium fast:** A giant isopod at the Toba Aquarium in Japan refused all food for 5 years and 43 days before dying in February 2014. This is among the longest documented fasting periods of any animal. The specimen, known as Number 1, had been in captivity since 2007 and was healthy and active throughout most of the fast period. Anatomy — built for the deep The giant isopod body is covered by overlapping calcified segments (pereonites) that provide rigid protection while allowing flexibility. When threatened, it can curl up so that only the tough shell is exposed — the same defensive strategy as its terrestrial relatives. It has seven pairs of walking legs, two pairs of antennae for chemosensory detection, large, widely spaced compound eyes with nearly 4,000 facets and a reflective tapetum that makes them shine in a camera light, and strong mandibles capable of processing tough material including fish skin and invertebrate shells. Giant isopods and humans Giant isopods are occasionally encountered as bycatch in deep-sea trawl fisheries. They are sometimes kept in public aquariums, where they are reliably popular. In northern Taiwan, local *Bathynomus* species have appeared in seafood restaurants and even in ramen — the flavor is reportedly similar to crab or lobster. They are harmless to humans. They have no venom and pose no threat to anything larger than their prey. Where exactly do giant isopods live? *Bathynomus giganteus* lives only in the western Atlantic, from Georgia to Brazil, including the Gulf of Mexico and the Caribbean. Its relatives cover the Indo-Pacific. For more than a century, almost any giant isopod hauled up anywhere was labelled *B. giganteus*. Taxonomic work has since shown that the genus *Bathynomus* contains around 20 species and that no species occurs in both the Atlantic and the Indo-Pacific. The old Pacific and Indian Ocean records of *B. giganteus* are now treated as misidentifications of other species. The western Atlantic has four species (*B. giganteus*, *B. obtusus*, *B. miyarei* and *B. maxeyorum*), and *B. giganteus* is the only one recorded off the United States. The rest are Indo-Pacific, with the highest known diversity, five species, off eastern Australia. None are known from the eastern Atlantic or the eastern Pacific. *B. giganteus* itself has been recorded from about 310 to 2,140 m. More than 80 percent of specimens come from 365 to 730 m on soft mud and clay bottoms of the continental slope. It prefers cold water. In a survey of Exuma Sound in the Bahamas it was common between 3.25 and 13 °C and became more abundant as the water got colder. Across the genus, the deepest record is 2,500 m for *B. kensleyi*. A few species range much shallower, such as *B. miyarei* at 22 to 280 m. ![Giant isopod (Bathynomus giganteus) on the deep seafloor, showing its large armoured segmented body](https://thesea.org/wp-content/uploads/v2-giant-isopod-how-big-is-the-biggest-giant-isopod-thesea-org-by-blane-perun.webp)Giant isopod (Bathynomus giganteus) on the deep seafloor, showing its large armoured segmented body How big is the biggest giant isopod? Most adult *B. giganteus* are 19 to 36 cm long. The largest confirmed specimen is about 50 cm. The often-repeated 76 cm figure comes from the popular press and was never verified. Scientists split *Bathynomus* into "giant" species, with adults mostly 8 to 15 cm, and "supergiant" species, with adults of 17 to 50 cm. *B. giganteus* is a supergiant, as are Indo-Pacific species such as *B. kensleyi* and *B. raksasa*, which may reach similar sizes. Even the "giant" species dwarf ordinary isopods, which rarely exceed 5 cm. A study of trapped isopods off eastern Australia found that the deeper the trap, the fewer the species and the larger they tended to be. Gigantism in the genus is old. Fossil *Bathynomus* are known from the Early Oligocene of Italy, with other fossils from Japan and Spain. The body plan has changed so little that species from Australia, Mexico and India look almost identical despite being separated for millions of years. Researchers link this lack of visible divergence to the near-darkness of the habitat, where looks matter less than in sunlit water. What do giant isopods actually eat? Mostly dead fish, with squid and shrimp next, and they will attack anything trapped or slow enough to catch. A study of the gut contents of 1,651 *B. giganteus* found that fish were the most common food, followed by cephalopods and decapod crustaceans, especially caridean shrimp and squat lobsters. They also take sea cucumbers, sponges and other slow-moving bottom animals. Fishermen know them as pests, because they get into trawl catches and trap lines and strip the fish. In one case a giant isopod was filmed latching onto the face of a dogfish shark caught in a deep-water trap and eating it alive. When a large food fall arrives, giant isopods gorge until they can barely move, then live off those reserves. That explains the extraordinary fasts seen in captivity. The Toba Aquarium animal, known as "No. 1", arrived on 9 September 2007, ate its last meal (a 50 g piece of horse mackerel) on 2 January 2009 and was found dead on 14 February 2014. Keepers noted that the isopod barely changed in weight during the fast, which is one reason the case is debated: it may have been absorbing small amounts of nutrition another way, or simply running a very slow metabolism in cold water. Temperature matters too. A related species, *B. doederleinii*, appears to stop feeding altogether below about 3 °C. How do giant isopods reproduce? Females brood large eggs in a pouch, and the young crawl out as miniature adults. Like other isopods, a mature female grows a marsupium, a brood pouch formed by overlapping plates on the inner edges of her legs. Her eggs develop there, and the young emerge as mancae: fully formed miniatures that lack only the last pair of legs. There is no larval stage, so giant isopods don't disperse as plankton, which may help explain why each species has its own regional range. Mancae can be up to 60 mm long at release. A giant female carries about the same number of eggs as a small isopod, but each egg is much larger, roughly in proportion to her body size. Studies of the seasonal abundance of juveniles and adults point to a breeding peak in winter and spring, probably linked to the timing of food supply. No females at all were collected until 1891, twelve years after the species was described from a single juvenile male caught off the Dry Tortugas during Alexander Agassiz's dredging work in the Gulf of Mexico. “The first time I saw one in a research vessel tank after a trawl, the reaction was instinctive — that immediate recognition of the pill bug shape, immediately followed by the brain refusing to accept the scale. It takes a moment to resolve.” — Blane Perun, TheSea.Org ![Giant isopod crawling over soft deep-sea mud beside a sea cucumber on the continental slope](https://thesea.org/wp-content/uploads/v2-giant-isopod-overview-thesea-org-by-blane-perun.webp)Giant isopod crawling over soft deep-sea mud beside a sea cucumber on the continental slope **Related on TheSea** - [Munnopsid Isopod](/munnopsid-isopod/) - [Diving Bell Spider](/diving-bell-spider/) - [Sea Fleas](/sea-fleas/) - [Terrible Claw Lobster](/terrible-claw-lobster/) - [Armored Snail](/armored-snail/) - [Carnivorous Harp Sponge](/carnivorous-harp-sponge/) - [Pink See-Through Fantasia](/pink-see-through-fantasia/) - [Ostracods](/ostracods/) - [Yeti Crab](/yeti-crab/) Frequently asked questions How big do giant isopods get? Most adults are 19 to 36 cm long. The largest confirmed specimen is about 50 cm. A 76 cm individual reported in the popular press has never been verified. For context, this is 30 to 50 times the size of a typical garden pill bug — the same body plan, dramatically scaled up. How long can a giant isopod go without eating? The documented record is 5 years and 43 days, set by a captive specimen at the Toba Aquarium in Japan. This is among the longest fasting periods of any animal. In the wild, extended fasts between meals are normal given the unpredictable food supply of the deep seafloor. What do giant isopods eat? Giant isopods are scavengers. They feed on whale carcasses, dead fish, squid, slow-moving invertebrates, and organic debris that sinks to the seafloor. When food is available they eat to extreme excess; between meals they can survive months or years on stored energy reserves. Where do giant isopods live? *Bathynomus giganteus* lives in the western Atlantic, from Georgia to Brazil, including the Gulf of Mexico and the Caribbean, at about 310–2,140 m, mostly 365–730 m on mud. Other *Bathynomus* species live in the Indo-Pacific, including Japan, Taiwan and Australia. Can you eat a giant isopod? Yes. Local *Bathynomus* species have been served in seafood restaurants in Taiwan and are occasionally eaten elsewhere in Asia. The flavor is reportedly similar to crab or large shrimp. They are not commercially fished on any significant scale. Are giant isopods related to pill bugs? Yes — directly. Both are isopod crustaceans in the order Isopoda. The familiar garden pill bug (roly-poly) and the giant isopod share the same fundamental body plan, including the overlapping armored segments and the ability to roll into a defensive ball. The deep-sea giant version grew to extreme size through the phenomenon of deep-sea gigantism. Are giant isopods found in the Pacific? Yes, but not *B. giganteus*. About 20 *Bathynomus* species exist. *B. giganteus* is western Atlantic only, and the Pacific and Indian Ocean animals belong to other species such as *B. doederleinii* and *B. kensleyi*. How do giant isopods reproduce? Females brood eggs in a marsupium, and the young emerge as miniature adults (mancae) up to about 6 cm long, with no larval stage. Explore crustaceans, worms & invertebrates Crustaceans, worms & invertebrates [Giant Isopod — the deep sea roly-poly that survived 5 years without food](/giant-isopod/) [Amphipods — tiny crustaceans found from mountain lakes to ocean trenches](/amphipods/) [Isopods — 10,000 species from pill bugs to deep-sea giants](/isopods/) [Cumaceans — comma shrimps of the seafloor sediment](/cumaceans/) [Krill — the tiny crustaceans that feed everything from fish to blue whales](/krill/) [Bearded Fireworm — reef bristleworm with neurotoxin-tipped stinging hairs](/bearded-fireworm/) Sources & further reading - Lowry & Dempsey (2006), the giant deep-sea scavenger genus *Bathynomus* in the Indo-West Pacific - Milne-Edwards (1879), original description of *Bathynomus giganteus* - Toba Aquarium records of giant isopod "No. 1", as reported by SoraNews24 (17 February 2014) - Briones-Fourzán & Lozano-Alvarez (1991), aspects of the biology of *B. giganteus* in the Gulf of Mexico Continue reading More from the Deep Ocean [Deep OceanGulper EelA deep-sea eel with a jaw that can unhinge to swallow prey larger than its own body. ](/gulper-eel/) [SharksGoblin SharkA living fossil from 125 million years ago with a slingshot jaw that strikes in 322 milliseconds. ](/goblin-shark/) [Deep OceanDumbo OctopusThe deepest-living octopus genus on Earth — named for fins that flap like ears at 7,000 metres depth. ](/dumbo-octopus/) BP Last updated May 18, 2026 Written by Blane Perun Blane Perun has been exploring Earth’s oceans, coral reefs, and marine life for over 25 years. Founder of TheSea.Org in 1999, underwater photographer, and explorer of 80+ countries. [About Blane Perun →](/about-blane-perun/) [More on Deep Ocean Life →](/bizarre-sea-creatures/)