Zoologist Philip Matthews has resolved the 100-year-old mystery of why Chaoborus midge can float in water. The findings of Matthews, who is a professor at the University of British Columbia, have been published in Current Biology. Chaoborus midge is also called the ‘phantom midge’ due to its near transparency. The transparency makes the larvae resemble tiny ghosts as they move through lakes, ponds, and puddles.Some fish regulate their buoyancy by inflating a swim bladder with oxygen unloaded from the hemoglobin in their blood.
In 1911, Nobel laureate August Krogh discovered Chaoborus larvae use a completely different mechanism, regulating their buoyancy using two pairs of internal air-filled sacs.
“These bizarre insects were floating neutrally buoyant in the water, which is something you just don’t see insects doing,” said Matthews.
“Some insects can become neutrally buoyant for a short time during a dive, but Chaoborus larvae are the only insects close to being neutrally buoyant.”When Matthews mounted the air-sacs of the larvae from the cattle tank on a microscope, they started glowing blue due to ultraviolet light illuminating the microscope’s stage.
The blue fluorescence was due to resilin, an almost perfect rubber found in parts of insects where elasticity is key, as in the elastic energy that powers a flea’s incredible jump.
“The weird thing about resilin is that not only is it really elastic. It will swell if you make it alkaline and contract if you make it acidic.”
With Ph.D. student Evan McKenzie driving experimental investigations, the researchers discovered that the insect doesn’t secrete gas into their air-sacs to make them expand. Instead, they change the pH level of the air-sac wall, the bands of resilin within the air-sac wall swell or contract in response, and the volume of the sac adjusts.
“This is a really bizarre adaptation that we didn’t go looking for,” said. Matthews. “We were just trying to figure out how they can float in water without sinking!”
