Isidore of Seville [7th century CE] (Etymologies, Book 12, 3:10): The ant-lion is so called either because it is equally lion and ant, or because it is the lion of ants. It is a small animal that is hostile to ants; it hides in the sand and kills other ants that are carrying grain. In this way it is like a lion to ants though it is like an ant to other animals.

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Worms 9.23): The lion of the ants, which is also called myrmicoleon, is explained by Andelmus from myrmin, which is an ant, and leon, which is a lion, as 'the lion of ants'. This worm is of the genus of ants, but much larger. While it is still small and has little strength, it feigns peace and modesty. But when it has increased its strength, robustness, and greatness of body, it despises its former associations and now accompanies the company of its ancestors. Then, gaining boldness, it hides itself in the secret places, and like a predator it ambushes the ants working for common purposes, and, like a robber, it snatches their burdens or even strangles and eats the ants themselves. But in the winter, the ants have stored food as if in a barn, but the myrmicoleon, which had prepared nothing for itself in the summer for use in the winter, plunders their labors and destroys them. This type of animal symbolizes hypocrisy and deceit in cloisters. - [Badke translation/paraphrase]

Albertus Magnus [ca. 1200-1280 CE] (De animalibus, Book 26, 20): Ant-lion is called the "lion of the ants" and also by another name, "murmycaleon". Despite what some people claim, this creature is not an ant during the first stages of its development. On many occasions I have observed this insect and demonstrated to associates that it resembles a tick and hides by digging a hemispherical hole in the gravel, where the upper pole of the cavity is the mouth of the ant-lion itself. As ants pass over the hole in search of provender, the insect captures and devours them; we watched this drama reenacted time and time again. In the winter the ant-lion is reputed to plunder the food stored by ants because it gathers nothing for itself during the summer. - [Scanlan]

Guillaume le Clerc [ca. 1210 CE] (Bestiaire, Chapter 12-13): [Chapter 12] There are ants of another kind / In Ethiopia—far up there; / Of dogs they have all the form / And are just of their size. / These are of a strange sort / For out of the ground and from the dust / They scratch up and dig pure gold; / So much that I cannot tell the sum of it. / And whoso wills to take this gold from them / Rues it sore and is sorry for it. / For straightway they pursue him / And if they reach him eat him quickly. / The folk who live near there / Know how savage and hot they are, / And that they have of gold great plenty, / So have a device ready: / They take mares, which have foals, / When they are young and milk-fed; / Three days they keep them starving, / On the fourth day they saddle them, / And to the saddles fix small boxes / As shining as is fine gold. / Between them and the country of the ants / Runs a river very swift. / With the mares to the river they come, / Keeping back the foals behind them. / Then they drive the mares across / Which are hungry both in heart and tooth. / On the other side is grass, lush / And thick and well-grown. / There go the mares feeding; / And the ants at once / When they see the boxes shining / Think they have a good place there / For to stow and hide their gold. / Then is no need to bid them / Fill and charge the boxes / With the good gold precious and dear. / So they all day carrying go / Until 1t draws towards dusk, / When the mares are sated / And have their bellies big and round. / When they hear their foals hinny / Then they hasten to return; / The river now they cross again. / The people take their gold and heap it up. / Now are they rich and opulent, / And the ants are very sad. [Chapter 13] There is still another ant / Which is none of those I told you of; / It has the name ant-lion. / Of ants this is the lion. / It is the smallest of all, / The most bold and most clever. / Other ants it hates bitterly. / In the dust quite deftly / It buries itself, so cunning it is. / When the others come laden, / Out of the dust it jumps on them, / And attacks and kills them. - [Druce translation]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book18.53): Formicaleon, that beast hath ye name of Formica, and of Leo, for as Isidore sayth, libro. 12.sayth, libro. 12. It is a beast with the lykenesse of an Ant, and of a Lyon, and is a little beast, and enimy to Ants: for he cometh théevishly into their place of purveiance, and eateth their corne, and so by wasting of theyr meate he is cause why the simple Antes dye néedes at last: and this Formicaleon is eaten of other beasts, as Antes bée, and may not defend himselfe by his owne strength, & is a maner kinde of Spider. Looke before de Aranea in littera A. - [Batman]