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Size Matters?

This macadamia nut plantation, an hour outside of Brisbane, 36.31. Is home to one of the very smallest members of the animal kingdom. These are a species of micro-ymenoptera known as Trichogramma. They are basically very small wasps and when I say small, I mean small. Can you see that? They're like specks of dust. They're less than half a millimetre long, but each one of those is a wasp. It's got compound eyes, 6 legs and wings. They've even got a little stripe on their abdomen.

And they're very precisely adapted to a specific evolutionary niche. The Trichogramma wasps may be small, but they are very useful.

They are natural parasites on insect pest species called the nut borer moth which attacks the macadamia nuts.

The micro-wasps lay their eggs inside the eggs of the moths, killing the developing moth larvae. What you're seeing here is the surface of the macadamia nut and here's a small cluster of moth eggs and there, you see the wasp is walking over the eggs.

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They're almost pacing out to a size to see whether the eggs are suitable for their eggs to be laid inside. And if we're lucky, there you go, you see that…

The wasps emerge just 9 days later as full-grown adults. At this scale, they live in a very sticky world, dominated by strong intermolecular forces. To them, even the air is a thick fluid through which they essentially swim, using paddle-like wings. Incredibly, these tiny animals can move about across several trees, seeking out the moth eggs.

But what I find more remarkable is that they do all this operating with very restricted brainpower. One of the limiting factors that determines the minimum size of insects is the volume of their central nervous system. In other words, the processing power you can fit inside their bodies and these little wasps are pretty much at their limit.

They have less than 10,000 neurons in their whole nervous system. To put that into perspective, most tiny insects have 100 times that many, but that's still enough to allow them to exhibit quite complex behaviour. These micro-wasps exist at almost the minimum possible size for a multicellular animals. But the scale of life on our planet gets much, much smaller. The wasps are giants compared to life at the very limit of size on Earth.