Midrash su Salmi 74:4

On his return, Vespasian dispatched Titus the Wicked, who when he reached Jerusalem said (Deut. 32, 37) Where are their Gods, the rock in whom they trusted? This is the same Titus the Wicked who profaned and shamefully violated the scrolls of the Torah; who vulgarly reviled and blasphemed the Holy One. What did he do after he had committed an adulterous act in the most sacred sanctuary? He took the sacred vessels of the sanctuary, wrapped them in the veil that was hanging in the holy place to sail with it to his capital and rejoice over his success, as it is said (Ecc. 8, 10) Then also do I see the, etc. At sea a storm arose and threatened to sink the ship; upon which Titus remarked: "It seems that their God has no power anywhere else except at sea. Pharaoh He drowned, Sisera He drowned, and now He is about to drown me also. If He be mighty, let Him go ashore and contest with me there." Then came a voice from heaven and said: "O thou wicked one, son of wicked man and grandson of Esau the wicked, go ashore. I have an insignificant creature in My world that is called a gnat. It is called insignificant, because it only receives but does not excrete, so go and fight with it." Immediately, after he had landed, a gnat flew up his nostrils and gnawed at his brain, for a period of seven years. One day he happened to pass a blacksmith's forge, when the noise of the hammer soothed the gnawing at his brain. "Aha!" said Titus, "I have found a remedy at last"; and he ordered a blacksmith to hammer before him. To a Gentile blacksmith he paid for this four zuzim a day, but to a Jewish blacksmith he paid nothing, remarking ot him: "it is enough for you to see thy enemy suffering so painfully." For thirty days he felt relieved, but after, it being used [to the hammering], the gnat did not heed it. We are taught that Rabbi Phineas, the son of Ariba said: "I myself was among the Roman magnates when an autopsy was made upon the body of Titus, and upon opening his brain they found therein a gnat as big as a swallow, weighing two selas." Others say it was as large as a pigeon a year old and weighed two literoth. Abaye said: "We have a tradition that its mouth was of copper and its claws of iron." Titus gave instructions that after his death his body should be burned, and the ashes thereof scattered over the surface of the seven seas, that the God of the Jews might not find him and bring him to judgment.