Why Don't Insects Live in the Ocean? Scientists Just Ruled Out One Possible Explanation Thanks to Deep-Diving Fly Larvae

An estimated six million species of insect—maybe even more—call Earth home. Yet for some reason, none of them are found in the ocean. Scientists have come up with a few possible explanations, and a popular one posits that the insect respiratory system would implode from water pressure.

Now, however, the deep-diving larvae in East Africa are challenging that notion. In a study published in the journal Science on July 23, researchers report that the larvae of the lake fly Chaoborus edulis regularly dive more than 650 feet below the surface of Lake Malawi thanks to strong air sacs that contain a stretchy protein. For the study, Matthews and his colleagues deployed an underwater sonar system in Lake Malawi, where billions of C. edulis live.

The data provided a window into the critters’ daily lives. In the morning, larvae descend to the lake’s hypolimnion—the deepest, coldest layer of water—at an average rate of about 25 feet per hour. The young bugs were recorded reaching depths of up to roughly 850 feet.

In the afternoon, they begin to rise toward the surface at an average rate of 65 feet per hour, finishing the journey by late evening. The cycle seems to help the insects evade predators. The fish can’t chase them in there,” Matthews tells Flora Lichtman on an episode of “Science Friday.” “Then they can float up at night when the fish find it really hard to see them and eat them.

And then they can spend their time eating the zooplankton up in the surface waters at night.” But how does C. edulis complete the trip? Studying some of them in the lab revealed their secret: a highly elastic protein called resilin. The larvae’s air sacs are covered in alternating bands of resilin and stiff cuticle, giving the respiratory structures the ability to contract and expand like an accordion to change the animals’ buoyancy.

The structures change in response to alterations in pH level in the walls of the air sacs. Then, to investigate how well the insect can withstand pressure, the scientists placed larvae and pupae—the next developmental stage—of C. edulis and three other species belonging to the Chaoborus genus in water-filled pressure chambers. C. edulis could withstand increasingly higher pressures as it developed, with its pupae able to endure water pressure up to 1,519 feet deep.