Scientists discover Lake Malawi insects surviving more than 200 metres below the surface

A new study has found that aquatic insects can survive at depths of more than 200 metres in Africa’s Lake Malawi, challenging the long-held belief that insects cannot live in such deep waters because their breathing systems would collapse under extreme pressure.

The study, published in the journal Science, found that the larvae of the lake fly Chaoborus edulis can withstand intense hydrostatic pressure and routinely descend into the lake’s deep waters.

The discovery overturns previous assumptions that insects cannot survive the extreme pressure of deep-water environments because of their tracheal breathing system, which delivers oxygen through a network of air-filled tubes.

“The absence of aquatic insects from pelagic marine habitats has been attributed to their air-filled tracheal respiratory system, which could implode at depth while undertaking diel vertical migrations to escape predatory fish. However, we found that the aquatic larvae of the lake fly Chaoborus edulis in Lake Malawi have modified their tracheal system into reinforced buoyancy-regulating air-filled sacs, allowing them to escape predatory fish by undertaking these migrations well over 200 meters deep into the lake’s anoxic hypolimnion during the day,” reads the study.

“The crush depth of their air sacs increases with each instar, with final instars resisting implosion at depths greater than half a kilometre. Contrary to expectations, these insects adapt to the extreme hydrostatic pressures of deep-water habitats, allowing them to coexist with pelagic fish.”

Lake Malawi, the second-deepest lake in Africa, has an average depth of 292 metres and reaches a maximum depth of 706 metres. The larvae of Chaoborus edulis play a vital role in the lake’s ecosystem by feeding on zooplankton while also serving as a food source for fish.

To understand how the insects survive at such depths, researchers used sonar technology to track the larvae as they moved through different layers of the lake. They also compared the species with related Chaoborus larvae found in shallower lakes, including Lake Victoria, which has an average depth of about 40 metres.

The researchers found that the larvae descend to depths exceeding 200 metres during the day, settling in the lake’s oxygen-free bottom waters to avoid predatory fish. After dark, they return to the surface to feed on zooplankton.

The study found that the insects survive these extreme conditions because of a modified tracheal system. Their buoyancy-regulating air sacs adjust as they move through shallower waters before becoming rigid at greater depths, preventing them from collapsing under intense pressure.

Laboratory tests also showed that the air sacs of the largest larvae remained intact when exposed to hydrostatic pressure equivalent to depths of about 500 metres, demonstrating their ability to withstand conditions far beyond those encountered during their daily migration.

According to the researchers, these specialised air sacs enable the insects to exploit deep-water habitats that are inaccessible to most other aquatic insects.

The team also noted that although aquatic insects account for more than 60 per cent of freshwater animal species, none are known to inhabit the deep open ocean. The findings suggest that the ability of Chaoborus edulis to withstand crushing pressure could reshape scientists’ understanding of the limits of insect life and raise the possibility that insects could one day colonise pelagic marine environments.

The researchers said the discovery provides new insight into how insects have adapted to survive in extreme freshwater environments and highlights the role of Lake Malawi’s unique conditions in driving those evolutionary adaptations.