The Elephant Hawk-moth (Deilephila elpenor) caterpillars come in both green and brown variants.
The Elephant Hawk-moth gets its name due to the way the caterpillar's head normally sticks out from its large body, like an elephant's trunk.
When threatened, the Elephant Hawk-moth will retract its head into its body, and assume a posture that makes it look somewhat like a snake.