Personally, Trader Jim isn't a nuisance creature. He does make for an interesting random encounter I admit!
On critters, the Ship's cat gets my first vote (Aliens movies are a bad influence on me--"the sudden cat appearnace syndrome"); Next the loveable(?) flyspiney (hedgehogs InnnnnSpaaaace! With Wings!). My favorite one was "Bertram" which an allied free Trader crew took to "losing" at starports, only to have him unerringly be found and returned. Later, they developed it into a Snipe-Hunt prank, pretending to have lost "Bertram" and the pool bet was how many locals they could get involved looking for him!
This was foiled by an enterprising group of PCs in a Brit friends campaign with a Trav Chronicle critter from Khes/Diaspora that shapechanges. They gave this new "bertram" back. Clever buggers they are!
The most bedevilling menace I created was an anerobic semi-intelligent fungiod , called the Fungi Bat-- it ate plastics, lived in low vaccum conditions, and was the bane of those passing thru asteroid systems. The geneered critter that ate dust Mites and dust on ships found the fungi bat a delicacy though. PCs had a treasure trove salavged ship, and discovered why it broke down trying to jury-rig her home. The Home port folks quarantined it til they could find a way to stop the menace. (and that took time, several adventures, and credits from their bar hopping!)
Last, Children properly run can be both nuisances, and good hooks.
Ditzie?
I saw her last with a Ship's crew entertaining her. I went ugly early, so I cannae tell you what happened next, save the Ship's doctor was giving out STD shots three days later.
(WEG)