My world is a medieval-magical setting like in "The Dark Eye". An extinct, magical elves-race had a technique to raise "bugs" from sand, but other materials were possible too. Those bugs usually had a maximum size of about 20 inches, depending on the work they were created for, obeyed all commands of their creator and needed a small amount of mana to stay "alive" (a normal Elf produced enough mana to maintain about 3 of those big bugs, more if they're smaller).
Usually, they did nothing, if they didn't follow a command. But those bugs are not dumb - they just did nothing, because they couldn't! The elves subconsciously disallowed unordered actions. As the elven race distincted, the bugs did so too, but one elf was magically turned to stone, and awoke thousands of years after his folks died. His 5 bugs are still "alive", because they drained him all the time. He ordered them to create more of themselves, unluckily he didn't notice that some bugs aren't following his orders (his subconscious couldn't surpress so many bugs).
Why should those indepent bugs multiply themselves?