A study found that when octopuses search for prey and care for their eggs, they analyze substances secreted by microorganisms with their suckers. This means they utilize a type of chemical sensor in addition to simply seeing or sensing touch through their arms.
A research team led by Professor Nicholas Bellono at Harvard University discovered that octopuses can differentiate between the conditions of prey and eggs by detecting the chemical signals of microorganisms growing on surface objects. The findings were published in the international journal Cell on 17th (local time).
◇Confirming microbial secretions on surfaces touched by suckers
Octopuses are curious marine animals, capable of sensing their environment and even tasting prey with the more than 200 suckers located on each arm. The suckers are densely populated with sensory neurons. Professor Bellono noted, "I was curious about what octopuses actually sense in their environment," and explained, "These sensory receptors are ideal for receiving signals from surfaces being explored."
This research began with an accidental observation. Rebecca Cephalopod, a postdoctoral researcher at Harvard, observed a California two-spot octopus (scientific name Octopus bimaculoides) sorting its eggs, discarding some in the process. After examining the discarded eggs under a microscope, specific microorganisms were found to be attached.
Based on this, the research team hypothesized that octopuses are detecting not the objects themselves, but the microbial communities growing on their surfaces. In fact, after culturing 300 species of microorganisms collected from the octopus's habitat, they experimented to see how each microorganism activated the octopus’s sensory receptors.
As a result, only certain specific microorganisms activated the sensory receptors. These microorganisms were primarily found on spoiled prey or eggs. For example, a microorganism growing on the shell of a dead crab secretes a molecule called H3C, which acts as a signal to the octopus that "this food is not fresh." Additionally, microorganisms on healthy eggs conveyed the information that they were "in good condition," prompting the octopus to continue caring for them.
The research team also experimented to see how octopuses reflect these signals in their behavior. When they presented an octopus with a plastic crab model coated with the H3C substance, the octopus recoiled or turned away. In contrast, when there was no H3C, it showed a reaction to grab and eat immediately.
◇Utilizing findings in studies on human-microbe relationships
Previously, Professor Bellono's research team announced in Cell in 2020 that the suckers of the California two-spot octopus transmit different neural signals when they touch prey compared to when they detect other objects. This indicates that they sense both touch and taste simultaneously.
In 2023, it was revealed that the sensory receptors in the suckers of octopus arms respond sensitively to oil molecules that do not dissolve in water. Most of the components of fish skin, octopus eggs, or seabed chemicals are not soluble in water. This means the octopus is checking whether an object touching its arms on the seabed is prey or eggs to care for.
The research team discovered that octopuses gather information not from the prey or eggs themselves, but through the mediator of microorganisms growing on their surfaces. Dr. Cephalopod explained, "Microorganisms continuously collect information about the surrounding environment, such as temperature and nutrient levels, and produce reflecting chemicals that inform the octopus, acting as a 'chemical interpreter.'"
In this regard, octopuses may help in studying the relationship between humans and gut microbes. While research has shown that gut microorganisms influence appetite, immunity, and emotions in humans, the complexity of this structure has made it difficult to clarify causal relationships. However, due to the relatively simple biological system of octopuses, the research team noted that they could clearly illustrate the connection between a single microorganism and specific sensory receptors leading to behavior.
The research team speculated that other animals might also exhibit similar behaviors in detecting microorganisms. Dr. Cephalopod stated, "Single-celled organisms known as flagellates form clusters and function as multicellular organisms when they detect specific microorganisms, suggesting that microbial signals may have been involved since the early stages of animal evolution."
Professor Bellono remarked, "By following a simple question about how octopuses use their arms, we were able to discover a new way that animals perceive the world," adding that "microorganisms are essential throughout life and evolution, representing yet another case of how deeply they impact physiology and behavior."
References
Cell (2025), DOI: https://doi.org/10.1016/j.cell.2025.05.033
Nature (2023), DOI: https://doi.org/10.1038/s41586-023-05822-1
Cell (2020), DOI: https://doi.org/10.1016/j.cell.2020.09.008