In the curse that G-d gave the snake is included the statement that G-d said to the serpent of (Bereishit 3:14) “you shall eat [1]dust all the days of your life.”
Seemingly, this is not much of a curse. For, being that dust is everywhere, the serpent seems ensured of his sustenance not matter where he may be.
However, Reb Mendel of Kotzk explains that this is in fact the greatest punishment:
It was if G-d told him: “I want nothing to do with you, and I do not even want to sustain you.”
[1] Emet Mkotzk Titzmach. Pg. 42
