Ok - so insects are a lot cooler than I thought.
Life in the Undergrowth commences with the descendants of the first creatures to clamber out of the water and onto land—the scorpions and their relatives. They made the transition some 400 million years ago, long before plants or our ancestors left the oceans. If you have never thought of scorpions as remarkable, Attenborough advises that you try to pick one up, perhaps with a pair of very long forceps. Whichever method you use it will not be easy, for scorpions possess advance warning systems that sense where you are and what you are doing. Their six pairs of eyes are strategically positioned so as to leave no blind spot, and while lacking sharp focus they are capable of detecting the tiniest variations in brightness—and thus movement. Yet they cannot be dazzled because each one has its own built-in "sunglasses," composed of pigment granules, which cover the lens as light increases.
Before it sees you a scorpion will either have "heard" you through the minute hairs on its claws, or detected your advance through a slit-shaped organ on the upper part of each leg, which is so sensitive to vibration that it can pinpoint the footfall of a beetle a yard away. Or perhaps it will have detected you with its pectines. These comb-like organs have no parallel among other living creatures. They are packed with nerve endings and are probably capable of smelling or tasting minute traces of chemical compounds in the ground over which the scorpion passes.
When a male scorpion meets a female scorpion, his mind is very much on the ground under his feet. You can tell this from his pectines, which scan the earth while he shakes his body back and forth. He then approaches the female and stings her on the soft flesh in the joints of a pincer. This seems to relax her, allowing him to grasp her claw in claw, bring her face to face, and begin a scorpion waltz. In the laboratory, scorpion pairs have waltzed for two days. But in nature half an hour or so seems to suffice, with the dance terminating when the male locates a really choice piece of ground (the long laboratory waltz may occur because the male cannot find the right type of ground). Soil texture is important in scorpion sex because instead of a penis males have a detachable spike which must be firmly implanted in the ground if insemination is to occur. Once the spike is in place the male maneuvers his partner so that her genitals are atop it. As the spike bends under her weight two tiny valves open, through which the sperm is released.
It's difficult for human beings to see scorpions at night, but it's easy for scorpions to see other scorpions. That is because scorpions produce bright green fluorescent light, which is clearly visible to them but invisible to the human eye. These superb adaptations have been honed by 400 million years of evolutionary experience during which countless billions of individual scorpions with blind spots, less sensitive pectines, or poor fluorescence have been weeded out, until finally we are left with the seemingly per-fect, yet utterly alien, creatures here described.
Locusts are simply grasshoppers with peculiar habits. There are ten species worldwide, and they are characterized by their roving swarms, which can appear out of nowhere and can devastate crops over a considerable area. Each continent has its own locusts, and each species has evolved independently from less troublesome grasshopper relatives. The Rocky Mountain locust—the sole species recorded from North America —was the most numerous and devastating of them all. Some idea of its abundance can be gained from the size of a swarm that visited Nebraska in 1875. Known as Albert's Swarm (named for the Weather Service pioneer who documented it), it is estimated to have consisted of 3.5 trillion insects. That's six hundred for every person living on earth today.