{
  "id": 9160548,
  "title": "How hermit crabs control growth to fit in their shells",
  "url": "https://urgent.news/2026/09/22/how-hermit-crabs-control-growth-to-fit-in-their-shells",
  "topic": "science",
  "section": "Science",
  "published": "2026-09-22T16:06:05.000Z",
  "source": {
    "name": "Futurity",
    "slug": "futurity",
    "url": "https://www.futurity.org/hermit-crabs-growth-shells-3345862/"
  },
  "original_language": "en",
  "account": "Scientists have long understood that hermit crabs adjust their growth to fit into their shells. However, the mechanism behind this process has been a mystery. Recent research sheds light on how these crabs regulate growth by altering how efficiently they use the food they consume. Caitlin Ball, a graduate student at Tufts University who led the study, explains that hermit crabs rely on empty snail shells for protection, and the optimal shell size may not always be available. When crabs find themselves in shells that are too small, they grow more slowly. The question remained: what is the underlying mechanism? To answer this, researchers compared the feeding behavior and waste production of crabs in shells that fit well versus those that were intentionally too small. Interestingly, the crabs in undersized shells did not consume less food. Instead, they excreted more frequently, indicating that they were expelling a higher proportion of nutrients rather than converting them into new tissue. Phil Starks, an associate professor of biology and the senior author of the study published in Invertebrate Biology, notes that this finding challenges the previous notion that growth is solely regulated by the amount of food consumed. Instead, it suggests that hermit crabs may adjust nutrient assimilation to control growth when external constraints, such as shell size, limit expansion. This research highlights a broader principle in biology: body mass isn't solely determined by food intake, but also by how efficiently an organism converts food into body mass. Starks emphasizes that this finding extends beyond hermit crabs, suggesting that across various species—including humans—the regulation of body mass can occur at the level of nutrient assimilation, not just appetite. While the study doesn't directly explain human weight variation, it underscores the complexity of energy absorption, partitioning, storage, and expenditure in different organisms. Jan Pechenik, a professor emeritus of biology and coauthor of the paper, adds that this discovery opens the door to further exploration of the mechanisms behind growth regulation in various animals, including humans. This study not only resolves a long-standing question about hermit crab growth but also paves the way for deeper insights into how animals adapt to their structural constraints through internal metabolic adjustments.",
  "summary": "\"For years, people observed the growth slowdown but couldn't identify the mechanism.\"",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}