What Happened to the Ancient Bug Giants of 300 Million Years Ago?
The Earth was home to giant insects, like in the movie Infestation. Okay, sure, that’s a bit of an exaggeration. They weren’t the size of a car, but there were mayfly lookalikes with 18-inch wingspans and dragonfly-like “griffins” with 28-inch wingspans.
Given their size and the fact that insects use a lot of energy to counter gravity during flight – not to mention that they have no lungs, with oxygen entering through tracheal tubes that look like small straws – scientists hypothesized that these ancient insects needed more oxygen to fuel their flight muscles.
Thus, according to the theory, the size of the insects was limited by the amount of oxygen diffused through their tracheal tubes and, therefore, by the concentration of atmospheric oxygen. Case in point: When these giant insects took flight at the end of the Carboniferous, around 300 million years ago, atmospheric oxygen levels were around 30%, compared to 21% today.
But now a new study published in Nature shows that the griffins (Meganeuropsis permiana) and other oversized insects could have survived with lower oxygen levels after all.
Read more: “Why birds can fly over Mount Everest”
Led by a team of researchers from South Africa, Australia, Germany, Ireland and the United States, the study used electron microscopy to illuminate the fine details of the flight muscles of modern flying insects. By analyzing the space occupied by tracheoles in 44 species of flying insects, the researchers determined whether tracheoles could indeed be a factor limiting oxygen supply.
The results showed that in most insect species, regardless of body size, flight muscle tracheoles took up 1 percent or less of the muscle space. Combined with evidence that insects growing in low-oxygen conditions develop more tracheoles, the researchers concluded that the size of flying insects was not limited by their tracheas. Basically, if a giant Carboniferous insect had needed more tracheoles, its flight muscles would have had enough space to accommodate them.
“If air oxygen really sets a limit on the maximum size of insects, then there should be evidence of compensation at the level of tracheoles,” Edward (Ned) Snelling of the University of Pretoria explained in a press release. “There is some compensation in larger insects, but it’s insignificant in the grand scheme of things.”
Why, then, were these mega-insects present in the Carboniferous, but not afterwards?
To begin with, they did not yet have any predators, birds or mammals, which later became a factor. But also, they were too big for their own good, as larger creatures are generally more vulnerable to extinction.
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Main image: Catmando / Adobe Stock
