No, believe it or not, that’s not a scene from the Alien movie; it’s the shed exoskeleton of a larval mayfly. Because insects are equipped with a stiff external skeleton, they can only grow by periodically discarding and replacing this exoskeleton. This molting process occurs repeatedly during larval development and is triggered by hormones released when an insect reaches the physical limits of its exoskeleton.
You may think that this process sounds fairly straightforward, maybe like wriggling out of a tight costume, but entomologists know that this is far from the case. During this stressful event, insects cannot eat and must remain still, leaving them vulnerable to predation. To make matters worse, a new study on mayflies has found that during this process, these insects can’t breathe either. Worryingly, the researchers found that this respiratory disturbance is worsened at higher temperatures, suggesting that global warming could be affecting aquatic insects in a previously unknown way. The work has been published in Freshwater Science.
Cloeon dipterum, or the common wetland mayfly, is an aquatic insect that is often used as an indicator of the ecological health of bodies of water. Lead researcher of the new study David Buchwalter has been studying how temperature and contaminants affect them for some time, including whether these factors influence oxygen consumption.
The respiratory system of aquatic insects consists of a branched network of trachea and smaller airways called tracheoles that deliver oxygen from the water directly to tissues. When an insect discards its exoskeleton, it also sheds large portions of the lining of the tracheal system. “It’s like having your lungs ripped out,” Joseph Bernardo, an ecologist at Texas A&M University who was not involved in the study, told Science. While it’s been known for some time that this happens, no one had measured how this affects oxygen consumption until now.
To find out more, Buchwalter placed mayfly larvae in tiny sealed chambers and waited for them to molt. They found that shortly before molting, the insects increase their oxygen intake by consuming 41% more than normal. Then, during the molting process, they stop breathing for up to an hour. Once the respiratory system is cleared, a compensatory surge in oxygen consumption occurs that lasts for around 2 hours. “Just like if you held your breath for as long as you could, and then breathed in a huge gasp,” Buchwalter told Science.
While this may sound extremely traumatic, Buchwalter has failed to find any evidence for harm triggered by this lack of oxygen. Furthermore, experts have pointed out that the insects must have evolved strategies to cope with this, and many insects can tolerate low oxygen levels anyway. However, what is worrying is that small temperature increases seem to cause the insects to molt more frequently, probably because they grow faster at higher temperatures. The team also observed that at higher temperatures, the erratic oxygen consumption becomes more extreme, which may make it more difficult to recover. This may explain why rising temperatures increase the risk of mortality in molting individuals, therefore indicating a previously unknown route by which climate change may negatively affect aquatic insects.