A homunculus is a creature summoned by a mage to perform some
particular task. They are particularly good at spying. They
are smallish creatures, but very agile. They can put their
victims to sleep with a venomous bite, but due to their size,
the effect does not last long on humans.

"Tothapis cut him off. 'Be still and hearken. You will travel
aboard the sacred wingboat. Of it you may not have heard; but
it will bear you thither in a night and a day and a night.
With you will go a homunculus that can relay your words to me,
and mine to you, across the leagues between at the speed of
thought.'"
[ Conan the Rebel, by Poul Anderson ]