Crawlers are small vermin minions summoned by Satyr Vierophants and The Verminancer in Tartarus.
When Chronos overthrew Lord Hades, the Satyrs moved from the Temple of Styx to the deepest regions of the Underworld to serve the Titan of Time. They brought the rat infestation with them, and these Crawlers now nest in large numbers inside the robes of their Satyr masters.
Crawlers will dart around at high speeds; look for the sunburst indicators (these appear around their hitbox) to determine where they are. They are fragile and deal only a small amount of damage, but can become a hassle if several groups are allowed to spawn at once.
A red summoning circle will appear at the feet of Satyr Vierophants shortly before 2-3 Crawlers appear. Their summoning can be interrupted if the Satyr channeling the spell is staggered or defeated quickly enough.