They are creepy smart.
Something about predatory nature of both insects seems to tune up their intelligence. Of course it never hurts having the BBC tell your story either.
Yep. To be a predator, you need to outwit your prey and think fast, so it's thought to be a natural INT grinder. `w´
Presumably, this could drive up the INT of prey too, but maybe it's cheaper to just be faster/harder to see? But you can't be THAT hard to see, and the speed only saves you in failed ambushes, so planning successful ambushes continues to reward the INT of predators (unless they just enter the speed arms race, like cheetahs or tiger beetles).
They probably can, internally; they just can't operate on tokens we recognize as numbers explicitly. For a computer analogy, take Windows Notepad - there's probably plenty of sorting, computing square roots and linear interpolation being done under the hood in the GUI rendering code - but none of that is exposed in the interface you use to observe and communicate with the application.
Rodents? Try insects [1]. In the late 40s and early 50s, when neural networks were first explored with great enthusiasm, some of the leading minds of that generation believed (were convinced, in fact) that artificial intelligence (or AGI in today's terms) is five/ten years away; the skeptics, like Alan Turing, thought it was fifty years away. Seventy years later and we've not achieved insect-level intelligence, we don't know what path would lead us to insect-level intelligence, and we don't know how long it would take to get there.
[1]: To those saying that insects or rodents can't play Go or chess -- they can't sort numbers, either, and even early computers did it better than humans.