Insects are limited by 2 things - their exoskeletons, which they need to shed every growing cycle but more by their breathing system - they do not have "active" lungs with which they draw in air. They have these tubules which just open to the outside world and air/oxygen just flows in and there is passive absorption by diffusion. So their size has to be small as air cannot travel quickly enough to all parts of an insect if it is too large. If one day an insect evolved more lung like devices, they would conquer the planet even more...
I saw few spiders in the video, Spiders belongs to the class Arachnida while insects are found in the class Insecta, main characteristics that distinguishes spiders from insects are:
Spiders doesn't have antennas like insects.
Spiders doesn't have wings at all. This is also true for some insects, but there are plenty of insects out there with either two or four wings.
Unlike the abdomen of insects, the abdomen of spiders isn't segmented.
Insects have three pairs of legs. Spiders has eight legs.
Spiders have eight simple eyes while insects have two more advanced, compound eyes.