Insects can be found in almost every environment on Earth. They live on every continent, at high elevations, in the freezing cold and at extremely hot temperatures.
Aquatic insects account for more than 60% of freshwater animal species, but none are known to inhabit the deep open ocean. It’s widely thought that their tracheal breathing systems would collapse under such pressure.
However, a study published in Science has found they can survive in one of Africa’s deepest lakes, at an astonishing depth of more than 200 metres.
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Lake Malawi is the second deepest lake in Africa, with an average depth of 292 metres – although it has a maximum depth of 706 metres. The aquatic larvae of the lake fly Chaoborus edulis are an important part of the lake’s ecology, acting as a food source for fish and feeding on zooplankton.
A team of researchers used sonar to track the larvae as they moved through the water column in the freshwater lake to avoid predatory fish.
They then compared Chaoborus species from shallower lakes, such as Lake Victoria, which has an average depth of 40 metres.
The scientists discovered that Chaoborus edulis frequently descended more than 200 metres to the lake’s oxygen-free bottom layer during the day to avoid being predated on by fish. They then returned to the lake’s surface waters to feed at night.
Unexpectedly, they found that this was due to a modified tracheal system. The larvae have reinforced buoyancy-regulating air-filled sacs that actively adjust depth in shallower waters, then become rigid at greater depths to resist crushing pressure.
When exposed to hydrostatic pressure in a laboratory environment, the air sacs of the largest larvae resisted collapse at depths equivalent to around 500 metres.
The findings suggest that insects could eventually colonise pelagic marine environments after all.
