I just watched one of the many inferior quality science videos on YouTube. It claims to have an explanation for why insects are attracted to light. After rejecting the theory that insects evolved to use the Sun for orientation, Insane Curiosity reaches the conclusion that… insects evolved to use the Sun for orientation – except that they face AWAY from the Sun. He claims that this instinct served insects quite well until humans came along and invented fire. You’d think that before Homo Erectus, fire was unknown in the world. What an odd assumption!
Even more so when we consider that insects arrived on the scene during the Ordovician period, about 480 million years ago. Later, during the Carboniferous period, Oxygen levels peaked at about 35%. I’ll quote from Grok:
Oxygen levels on Earth were likely highest during the Carboniferous period, roughly 300 million years ago, peaking at around 35% of the atmosphere compared to today’s 21%. This was driven by massive plant growth and swampy forests that produced oxygen through photosynthesis while sequestering carbon. Data from ice cores and fossil records, like those studied by geochemists such as Robert Berner, support this, showing elevated O₂ levels due to high plant productivity and low decomposition rates in oxygen-poor swamps. Exact timing and levels vary slightly in models, but the Carboniferous stands out.
How long did Oxygen levels remain high? Again, I’ll quote from Grok:
Elevated oxygen levels during the Carboniferous period, peaking around 35% of the atmosphere, likely persisted for approximately 50–60 million years, from about 330 to 270 million years ago. This duration is inferred from geochemical models, such as those by Robert Berner, and fossil evidence indicating sustained high plant productivity and low decomposition rates in swampy environments. Levels began to decline toward the end of the Permian period (~270 million years ago) due to changes in climate, vegetation, and tectonic activity, gradually approaching modern levels of ~21%. Precise durations vary slightly depending on the model and proxy data used.
During this very long period of time, fire would have been extremely common. Even the slightest spark would be enough to ignite a conflagration. Another consequence of such high levels of Oxygen is that insects grew to great sizes. Insect do not have lungs. Instead, they “breathe” through their exoskeletons. They’re small today because Oxygen levels are low, and they cannot absorb enough of it to support large bodies.
This means that insects would have been an important part of the diet for many creatures during this period. In fact, they would have been a staple for many species.
How might the insects have avoided predators? They would have congregated near fires. Fire scares away predators, most of which were flying creatures with relatively slow reproduction cycles – at least compared to insects. Even though many insects would be burned by the fire, or overcome by the smoke, they wouldn’t care; their sheer numbers would make such sacrifices inconsequential. Those who kept away from the fire would be easy prey for flying predators, and they would have died in much larger numbers. It would have made sense for predators of insects to stay away from fire, but for insects to remain close to it.
I don’t know if I’m the first to think of this explanation, but I haven’t found it anywhere else; it popped into my head at 2 AM, when I should have been sleeping.
