Kolektinbug

If you are bitten by the Kolektinbug, you will turn into a collector, and then you will need a bigger house.

In Chapter 9 of The Enchanted Duplicator, Jophan encounters the hucksters, one of whom tries to sell him one of the "adorable little pets to beguile the tedious hours."

The Kolektinbug is a "captivating jewel-like creature resembling a lady bird, gaily coloured and beautiful to look upon," but it soon turns into "a hideous leech-like creature, bloated with the life-blood of its victim."

Also see: Completist.