Mosca (the gadfly) is a parasite; this bestiary name encompasses the simple character of Volpone's servant. Mosca is only one step higher in the social scale than the three deformed fools of Volpone's household: the dwarf, the hermaphrodite, and the eunuch. He is socially deformed, a fellow of no birth or blood.
Mosca lives by his wits; he has no possibility of advancement in the Venetian world, and he is therefore free of the folly of greed. He takes his needs from the treasures of others, and he takes only his daily needs.
The parasite's freedom from the normal ambitions of human nature makes him a formidable judge of it. He uses this knowledge to mock the frailties of his fellow men, and his only pleasure is in his wise observance that, if he is not noble, they are parasites. It is only when Volpone's need for cozening puts the weapon of financial advancement into Mosca's hands that the gadfly tries to live by his own means. Mosca's sudden opportunity for gain makes him vulnerable to the folly of greed, which eventually pulls down the charming and inventive rogue. This comic character flaw is particularly ironic in Mosca; it is the very folly he has been so delightfully mocking for five acts. Did he for a moment forget that "almost all the wise world is little else, in nature, but parasites or sub-parasites"?