I had this game when I was a kid and only gave it a few goes since I had no instructions and couldn't figure out how to play. Now, thanks to the magic of the internet, the instructions are available: https://archive.org/details/softside-magazine-selections-55-1983-04Atari/page/n9 (around page 8 or so)
Not a classic game by any means, but it's fun once you understand what to do. Eat anything that's red, and anything that's dark yellow. (Certain bugs and fruits cycle between dark yellow and white - eating them when they're white causes a loss of energy.) That's about it - survive as long as you can!
Muffy St. Bernard - 15/11/2009
Eat the purple spiders to gain energy, avoid everything else. But since your energy is always dropping, be sure to "pace yourself" or you won't have enough purple spiders to keep going.
At least I think that's how it works. There must be more too it, though, otherwise you're bound to run out of energy by level three.