Sheydim in the Shade: Demons of the Three Weeks

Another thing: "all her pursuers overtook her in the narrow places" (Lam. 1:3): on days of distress, from the seventeenth of Tammuz to the ninth of Av, when ketev meriri are found. Just as it says, "[from] the plague that stalks in the darkness, or the scourge [ketev] that ravages at noon" (Ps. 91:6). Rabbi Abba bar Kahana and Rabbi Levi: Rabbi Abba bar Kahana said, it spoils study at midday, from the beginning of the sixth hour to the end of the ninth. And Rabbi Levi said, it spoils study at midday from the end of the fourth hour to the beginning of the ninth, and it walks neither in the sun nor in the shade, but in the shade adjacent to the sun. Rabbi Yochanan and Rabbi Shimon ben Lakish: Rabbi Yochanan says, it is all full of eyes, scales upon scales, hairs upon hairs. And Rabbi Shimon ben Lakish says: it has one eye set in its heart, and anyone who sees it falls over and dies. And it happened that one pious man saw it, and he fell on his face and died, and some say it was Yehuda the son of Rabbi [Yehuda ha-Nasi].

And Rabbi Yitzḥak said: Anyone who recites Shema upon his bed, demons stay away from him. As it is stated: “But man is born into trouble, and the sparks [reshef ] fly [uf ] upward” (Job 5:7). The word fly [uf ] means nothing other than Torah, as Torah is difficult to grasp and easy to lose, like something that floats away, as it is stated: “Will you set your eyes upon it? It is gone; for riches certainly make themselves wings, like an eagle that flies into the heavens” (Prov. 23:5). The word “sparks” means nothing other than demons, as it is stated: “Wasting of hunger, and the devouring of the sparks [reshef] and bitter destruction [ketev meriri], and the teeth of beasts I will send upon them, with the venom of crawling things of the dust” (Deut. 32:24).

The ketev meriri: There are two types of ketev demons, one that comes before noon in the morning and the other one comes in the afternoon. The one that comes before noon is called ketev meriri (Deut. 32:34), and it appears in a jug of kutaḥ, a Babylonian spice, and continuously revolves around inside it. The ketev in the afternoon is called ketev yashud tzaharayim (Psalms 91:6), and it appears inside the horn of a goat and revolves around inside it like a sifter.... From the first of Tammuz to the sixteenth of that month, these demons are certainly found. From here onward it is uncertain whether they are found or whether they are not found. And they can be found in the shadow of a sea squill that has not grown a cubit, and in the shadow of objects in the morning and evening when their length is less than a cubit. And they are mostly found in the shadow of a privy.

When Moses went up on the mountain, he said this psalm (91), “Who dwells in the shelter of the Most High,” since he was dwelling in the shadow of the Holy Blessed God, most high and awesome..... “The plague that stalks in the darkness, or the scourge that ravages at noon" (Ps. 91:6). This is the ketev meriri, for which whatever sees it - whether human, domestic animal, or wild beast - will not stay alive in the world. How is it made? Its head is like a calf, with one horn in the middle of his forehead, and it is made of obsidian. And meriri rules around noontime, from the seventeenth of Tammuz until the 9th of Av.

"From the plague that stalks in the darkness." Our rabbis said: that is a demon.... Rabbi Huna said in the name of Rabbi Yosei: the ketev meriri is made of scales upon scales, hars upon hairs, and eyes upon eyes. It sees with a single eye and that eye is inside its heart. It rules neither in the sun nor in the shade; rather, [it rules] between the sun and the shade. It rolls around like a ball, and it rules from the fourth hour of the day until the ninth, and it rules from the Seventeenth of Tammuz until the Ninth of Av. Whoever sees it falls over and dies.

One must take care from the 17th of Tammuz until the 9th of Av not to go out between the fourth and the ninth hours [of the day] (because at those [hours] the ketev meriri rules). And one must not strike students on those days.