This song says about "Little things" that we never notice but they are really important.
As you can see in video clip and hear in lyrics it's expressed like "people ignoring bugs".
~"I'm an animal trapped in your hot car"
~"I'm in the middle of your picture Lying in the leaves"
~"I'm just an insect trying to get out of the night"
These two quotes shows that Radiohead wanted to express idea by using that "insect" thought. By using "I'm (...)" Radiohead shows that the insect is talking and asking to be found or just seen. However it's not about bugs, it has deeper meaning as I mentioned before. Like "big things can't happen without little ones" .
Radiohead philosophy is usually related with NATURE (for example song: "There There"). Same thing happened now - this song express deep meaning by using Nature. It might be true that THAT "INSECT" talking in song is something like "Help" or "Savior" that people don't notice and live depressed life.
