47 But, you say, if God is not the parent and father of souls, by what sire have they been begotten, and how have they been produced? If you wish to hear unvarnished statements not spun out with vain ostentation of words, we, too, admit that we are ignorant of this, do not know it; and we hold that, to know so great a matter, is not only beyond the reach of our weakness and frailty, but beyond that also of all the powers which are in the world, and which have usurped the place of deities in men's belief. But are we bound to show whose they are, because we deny that they are God's? That by no means follows necessarily; for if we were to deny that flies, beetles, and bugs, dormice, weevils, and moths, are made by the Almighty King, we should not be required in consequence to say who made and formed them; for without incurring any censure, we may not know who, indeed, gave them being, and yet assert that not by the Supreme Deity were creatures produced so useless, so needless, so purposeless, nay more, at times even hurtful, and causing unavoidable injuries.
Source: Against the Heathen (New Advent)