Alien tick

The tick-like bugs are a race of insects encountered by the Destiny Expedition during an off-world mission. They attach themselves to the back of the victim's next and release a toxin which heightens negative emotions, manifesting them as hallucinations of the victim's worst fears. Any attempt to remove them causes them to burrow deeper while releasing a large amount of toxin, potentially killing their host. In this event, they move to someone else nearby.