An insertion mechanism for a wearable drug delivery device includes a needle hub, a needle coupled to the needle hub, a flexible boot removably coupled to the needle hub, and a cannula coupled to the flexible boot. The needle hub, the needle, the flexible boot, and the cannula are movable between a first position and a second position. Upon moving the needle hub, the needle, the flexible boot, and the cannula from the first position to the second position, the cannula engages a floor member to restrict movement of the cannula and the flexible movement towards the first position.