You Might Think of Shrimp as Bugs of the Sea. But a Remarkable Discovery Shows the Opposite: Bugs Are Actually Shrimp of the Land A recent study suggests that insects branched out from crustaceans on the tree of life Riley Black - Science Correspondent April 9, 2025 8:00 a.m. A species of remipede known from the Caicos Islands. The photograph was taken by a member of a multinational team looking for rare species. Remipedes are crustaceans that are close relatives to insects. Jørgen Olesen / Natural History Museum of Denmark, Brett Gonzalez, Karen Osborn, GGI Shrimp look an awful lot like bugs. The exoskeletons, jointed legs and compound eyes of both groups of living things give them more than a passing resemblance to each other, so no wonder some people call shrimp-like crawfish “mudbugs,” and a tattoo reading “shrimps is bugs” became a viral meme for underscoring the resemblance. But the tattoo got the reality backwards. Shrimp are not bugs. Bugs—or, more properly, insects—are technically a form of crustacean. Biologists of many different subdisciplines categorize life in a field called systematics. Living things of all sorts, both extant and extinct, are constantly being compared and evaluated to build what we so commonly think of as the tree of life. The addition of new species and novel analyses are constantly reshaping that evolutionary tree, and sometimes the category changes shift more than just a few twigs but entire evolutionary branches. Birds are now known to be dinosaurs, for example, whales are technically hoofed mammals called artiodactyls, and, thanks to a 2023 study in Molecular Biology and Evolution, insects have been shifted into the same group as shrimp and crabs called pancrustacea. The realization that bugs were close relatives of crustaceans took almost a century of curiosity to uncover. Paleontologist Joanna Wolfe of Harvard University, one of the authors of the 2023 study, notes that researchers noticed some insects and crustaceans had the same structures in their eyes and nervous systems. The resemblance could have been the result of convergent evolution, when two groups independently evolve in the same way, and so the idea that insects are modified crustaceans didn’t catch. But the hypothesis didn’t fully go away, either. In 2013, Wolfe and colleagues found that insects were the sister group, or next closest evolutionary relatives, to crustaceans called remipedes—which live in undersea caves and are the only venomous crustaceans. Remipedes were supposed to be oddballs that were shaped in strange ways due to their lives in caves. Now they were coming out as the closest relatives to the flies, mantises, bees and other insects we see around us on land. “At that time, I was shocked and thought there was something wrong with our results,” Wolfe recalls, only to have additional evidence make the connection between insects and crustaceans stronger. The 2023 analysis, based on genetic data, found insects next to remipedes in the middle of the various crustacean subgroups. Specifically, insects fit within a wide group of crustaceans called allotriocarida that not only includes remipedes, but also other unusual groups such as shrimp-like branchiopods and worm-like cephalopods sometimes called “horseshoe shrimp.” To put it another way, insects are to crustaceans as bats are to mammals—a subset that belongs to a broader group despite seeming so different from their closest relatives. Systematic shifts do far more than simply rearrange who’s related to whom. “Systematics allow us to make sense of the complexity of life,” says Smithsonian National Museum of Natural History paleontologist Advait Jukar. “When we recategorize species into new groups we can look at patterns of how that group might be diversifying and the various environmental and ecological factors.” Insects, like those above, fit right in the middle of the broader crustacean family tree. Richard Ross, The Image Bank via Getty Images When birds were recognized as dinosaurs, the change did more than reshuffle their place on the evolutionary tree. “The change showed us how characteristics that we typically associate with birds today, such as feathers, hollow bones and air sacs, were widely found within Dinosauria,” Jukar says. Paleontologists began finding more feathered dinosaurs and dinosaurs with traits previously associated with birds, such as complex systems of air sacs as part of their respiratory systems, once the connection was made. The newly understood relationship between birds and other dinosaurs has allowed experts to better understand why only birds survived the mass extinction of 66 million years ago. Comparisons between birds and bird-like dinosaurs revealed that adaptations for eating seeds and nuts that some birds developed during the Cretaceous allowed them to survive while bird-like raptors perished. The recognition that whales are hoofed mammals occurred around the same time as birds were found to be dinosaurs. The shift had a deep effect on how paleontologists carried out their research as well as the identity of the blubbery mammals. Prior to the 1990s, the earliest whales were thought to have evolved from carnivorous mammals called mesonychids. The beasts, sometimes called “wolves with hooves” because they looked like canids with hoof-like toes, were some of Earth’s most prominent carnivores around 55 million years ago, the time when amphibious whales such as Pakicetus began swimming in the shallows. But genetic evidence kept grouping whales close to hippos and other mammals with hoofed toes, called artiodactyls. Experts debated the connection, but by 2001 paleontologists uncovered early whale ankle bones that possessed traits only seen among artiodactyls. The recognition shifted where whales fit in the mammalian evolutionary tree and recalibrated what sort of ancestral creatures paleontologists should be looking for, yielding the 2007 discovery that whales most likely evolved from small, deer-like creatures in ancient India. Without the recognition that whales are artiodactyls, the relevance of those ancient, hoofed creatures to the origin of whales would have been entirely missed and paleontologists would still be wondering where orcas and minke whales came from. In the case of the bugs, Wolfe notes, the recognition that insects shared a close common ancestor with remipedes helps narrow down where and how insects originated. “For me, the exciting part for insects is the recognition that they do not come from a terrestrial ancestor,” Wolfe says. Until recently, the ancestors of insects were thought to be more millipede-like and evolved once invertebrates began to live on land. Now, Wolfe notes, the closest relatives of insects are wiggly crustaceans that live in marine caves. The connection doesn’t mean that remipedes embody the exact ancestral form of the first insects, but rather that their close relationship will cause experts to rethink where insects came from and how they evolved. The effort will require tracing the ancestry of remipedes and other crustaceans, as well as searching for insects in the fossil record—both from new fossil sites and perhaps miscategorized fossils already in collections. “There’s a complicated history and still missing pieces,” she notes, but now biologists have a better sense of what to search for. Bugs are crustaceans, and now experts can begin to wonder how that came to be. Get the latest Science stories in your inbox.

A recent study suggests that insects branched out from crustaceans on the tree of life