Small, defenceless and tending to gather in herds, parasprites are easy prey for many of the other creature that live in the environments they make their home. They only survive due to their tremendous birth rate, breeding through pathogenesis (seemingly vomiting a new parasprite) at a rate that can see their numbers multiply exponentially within hours. Perhaps to feed this tremendous ability they are capable of consuming enormous amounts of food within moments, with a ferocity that makes one glad that they are herbivorous.
Unfortunately all these traits mean that outside their natural environment they quickly become very dangerous, as without predators their numbers increase to a point where they can strip a whole landscape bare. Zecora reported that whole towns had been destroyed by parasprite infestations, and that if Ponyville indeed had one it was surely “doomed”.
Fortunately they are not very intelligent, and have one key weakness. Certain types of music will hypnotise them, causing them to happily follow the commands of the music without complaint. Since they are heard uttering musical purrs and move in packs, this may be a form of communication for them.
Parasprite is a term often used to denote a troll, normally in the phrase “Don't feed the parasprites”.
The Parasprites take clear inspiration from Star Trek’s Tribbles. Spike’s reference to feeding them after midnight also brings to mind the film Gremlins.