Today’s last beast from beyond – Jaekelopterus rhenaniae – was a massive sea scorpion. This pincered psycho lived around 390 million years ago and could grow up to 2.5m long. They were actually freshwater buggers and would defo have ruined your sunday afternoon swim in the lake. It’s claws alone were nearly 50cm long. Just the right sort of length to sever a human head. OMG.

So how did insects get so big back then, and why don’t they get that big anymore?

Insects don’t breathe through their faces like we do, they have holes all over their bodies called spiracles which are attached to a network of internal pipes called trachea that travel throughout the body feeding its cells with oxygen. The bigger the insect gets, the wider the pipes have to be and this puts pressure on other organs.

Back in the distant past when the earth was a lush, dense, tropical jungle, the oxygen levels were much higher in the atmosphere. Rather than the air being about 20% oxygen, it was more like 30-35%. This meant that the insects could evolve much bigger but keep their air pipes small allowing them to turn into nightmarish jungle beasts.

As you can probably deduce, when oxygen levels dropped the insects got smaller too. But the story is a bit more complicated. About 150 million years ago oxygen levels were still on the rise, but the fossil record shows a steep drop in insect size. What happened? One theory is that 150 million years ago birds evolved and kept these grizzly buggers in check. There was also another dip in insect size around 95 million years ago, this may have been due to birds getting more maneuverable, and also the magnificent rise of the bats.

Why ever it was that the insects shrank, I for one am incredibly glad that they are now “normal” size. Let’s all raise a glass to the birds and the bats.

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