viper, adder, asp
蝮 centers on a specific type of venomous snake: a viper, adder, or asp. The meanings are all closely related, referring to dangerous snakes with a venomous bite.
蝮 combines 虫 (insect/reptile) with 复, which likely contributes the sound フク. The character specifically denotes a venomous snake.
The left side 虫 signals a creeping creature, and the right side 复 looks like a coiled, dangerous shape. Picture a viper coiled and ready to strike.
For フク, imagine a viper hiding in a fuku (服, clothing) pile: fuku -> フク, and the snake strikes when you reach for your clothes.