A sperm whale can dive beyond 2,000 meters, enduring pressure that would crush steel, yet researchers continue to find organisms living inside their bodies that are as remarkable as the animals themselves. Routine examinations of dead whales have produced discoveries that range from massive blockages caused by the animal’s own biology to parasitic worms longer than most vehicles.
Sperm whales are the largest toothed predators on Earth, with males reaching lengths of around 18 meters. Their lives center on deep dives to hunt giant squid and other prey in total darkness. They typically dive between 600 and 1,000 meters during normal feeding trips, and some tagged individuals have been recorded past 2,000 meters. While diving, the whale shuts down nearly all non-essential bodily functions: digestion stops, blood is pulled from the skin and limbs and redirected to the heart and brain, and a large oil-filled organ in the head called the spermaceti organ helps control buoyancy and focus sound for echolocation.
The scars on many sperm whales, left by squid hooks and suckers, are some of the only physical proof scientists have of these deep-water battles. The whales also have functional teeth only on their lower jaw, and many adult males carry teeth that are chipped or worn down from years of gripping struggling prey. An animal built this tough might seem to have little to fear, but what researchers continue to find inside their bodies during necropsies tells a more complicated story.
Centuries ago, whalers were already encountering strange material inside sperm whales, though they rarely understood its significance. They sometimes found waxy, foul-smelling lumps in the intestines of sperm whales, which, when dried and aged, developed a pleasant scent and became a prized substance in perfume making. That material, ambergris, was so valuable that it was sometimes called floating gold, since chunks could also wash up on beaches after passing through a living whale. Whalers also regularly examined the stomach contents of whales they caught, finding squid beaks that revealed what the animal had been eating in the deep sea. What none of those early whalers documented was a parasite of significant size, since identifying something like a tapeworm measuring several meters long required scientific training and tools that did not exist on whaling ships.
In May 2023, a 13-meter male sperm whale washed up dead at Playa Los Nogales on the island of La Palma in Spain’s Canary Islands. A necropsy performed within 48 hours found a solid mass blocking the whale’s lower colon. The mass measured about 50 centimeters across and weighed 9.5 kilograms, and it was made of hardened waste material, the same kind of ambergris that perfume makers prize when it washes ashore on its own. Researchers found squid beaks and fish lenses embedded in the mass, along with a 5-centimeter metal fishing hook sitting nearby in the stomach contents. Lab tests identified three different types of intestinal bacteria in the tissue, including Edwardsiella tarda and Clostridium perfringens, and researchers concluded that the blockage led to a fatal blood infection. The whale also showed damage in its heart muscle, a sign that the infection had spread well beyond the original blockage site by the time the animal died. The case showed how much can go wrong inside a sperm whale’s digestive tract without any visible wound on the outside.
The stomach of a healthy sperm whale is typically filled with squid beaks, the hard, indigestible parts of squid that the whale cannot break down. Over time, these beaks can clump together into dense masses, sometimes contributing to the same kind of fatal blockage seen in the La Palma case. Ambergris likely forms as a protective coating that the whale’s body produces around these sharp remnants, which is why chunks of it are often tangled together with beak pieces.
Modern pollution adds another danger on top of that natural buildup. In 2020, researchers at Spain’s El Valle Wildlife Rescue Center found a young sperm whale on a beach in southern Spain carrying a large amount of plastic in its stomach, which they believed had killed it. In 2018, another sperm whale stranded in Spain was found with a mass of tangled ropes, fishing nets, and plastic debris that weighed roughly 220 pounds. Similar cases have been recorded around the world, with whales found carrying plastic bags, packaging, and rope fragments packed so tightly that food could no longer pass through the digestive tract. Marine biologists now treat plastic ingestion as one of the clearest and most preventable threats to the species.
The most unusual discovery inside a sperm whale, however, was not trash at all. It was a parasite. Deep inside the reproductive tissue of pregnant sperm whales lives a roundworm called Placentonema gigantissima, first described by Soviet researcher A. G. Gubanov in 1951. Guinness World Records recognizes it as the longest nematode ever documented, with specimens reaching roughly 8 meters in length and several centimeters thick, found coiled inside the whale’s placenta. Because it lives specifically in placental tissue, researchers only encounter it while examining pregnant females, making each documented specimen a rare find.
An even longer parasite lives inside the intestines of sperm whales and other large whales. A tapeworm called Tetragonoporus calyptocephalus, previously known as Polygonoporus giganticus, has published estimates placing its maximum length near 30 meters, with some older reports claiming specimens closer to 40 meters. Pulling one out fully intact is extremely rare, since the worm’s body is fragile and easily broken. The worm grows segment by segment, with a small attachment point fixing to the intestinal wall while new segments keep forming behind it. Each segment carries its own reproductive organs, and some individual worms have been described with as many as 45,000 segments strung together.
The existence of such large parasites inside a well-studied animal raises an obvious question: if something this big could go unnoticed for so long, what else might be hiding inside whales that scientists have not yet had the chance to examine?
That question became more urgent in 2025 with a discovery involving a much smaller relative, the pygmy sperm whale. Researchers studying decades of stranding records found three previously unknown types of Helicobacter bacteria hiding inside the stomachs of stranded pygmy sperm whales. All four infected whales in the study showed serious digestive damage, including inflammation, ulcers, scarring, and parasite infestations, though scientists have not yet confirmed the bacteria as a direct cause of death. Pygmy sperm whales are difficult to study because they spend most of their lives far from shore, travel in small groups, and rarely surface long enough for observation. They weigh up to 1,000 pounds and rarely grow past a few meters long, but they share similar deep-diving habits and squid-heavy diets with their much larger relatives. Most of what scientists know about their internal health comes from animals that wash up dead or dying.
The discovery of new bacteria inside an animal this well-documented has prompted researchers to reconsider older stranding cases. If such significant bacteria went undetected for decades, some scientists now wonder how many past stranding cases, originally blamed on plastic, ship strikes, or unclear causes, might have involved an unseen infection playing a hidden role in the animal’s death. That possibility does not overturn what is already known about plastic pollution or fishing gear killing whales, since cases like the large plastic mass in Spain remain clearly documented. It does mean researchers are now going back through preserved tissue samples from past strandings with tools that did not exist when those whales were first examined, checking for bacteria and parasites that no one had thought to look for. This re-examination is slow and careful work, and it rarely produces a single dramatic answer. Instead, it tends to reveal that a death chalked up to one obvious cause may have involved several factors working together. Modern genetic sequencing tools now allow researchers to identify bacteria strains from tiny preserved tissue samples collected decades ago, meaning old specimen archives in university freezers could still hold answers that were not looked for when the samples were first frozen.
Even with modern tools, many basic questions about what lives inside a sperm whale remain unanswered. No one knows how common Tetragonoporus calyptocephalus infections are across the global sperm whale population, since finding one fully intact inside a dead whale depends entirely on luck and timing during a necropsy. No one has confirmed whether the newly discovered Helicobacter bacteria in pygmy sperm whales kills its host directly, weakens its immune system enough to let other problems take over, or simply exists alongside more serious health issues. Researchers also still do not have a clear picture of how often ambergris blockages happen at sea, since most cases only become visible once an already dead whale washes ashore. Whales that die from internal problems far out in the open ocean likely sink or are scavenged long before anyone can examine them, meaning every documented case might represent only a small visible fraction of a much larger pattern happening out of sight.
None of this changes the basic well-documented picture of the sperm whale as one of the toughest predators in the ocean, built to survive crushing pressure, total darkness, and battles with animals nearly its own size. What has changed is how confident scientists can be that they already understand everything happening inside that animal once it dies. A worm stretching longer than a city bus, bacteria nobody had ever classified, and a blockage built from the whale’s own natural defenses have all turned up inside bodies that had already been studied for decades. Every new necropsy continues to show that the sperm whale’s toughest battles are not only fought against squid in the deep. Some of the strangest survival stories are happening quietly inside its own body, and researchers are only now starting to catch up with what has been hiding there all along.
