Spitty

Spitties are much fatter than other maggot forms, possess a face like Chargers, but have only half health of a Charger. They spit a blood shot ahead of them while slowly crawling along aimlessly. They have a slow firing rate, and because they ignore Isaac, their shots are easy to avoid.

They also can be summoned by other monsters and bosses, such as the Grub, Pestilence, and Chub's orange champion variant.

Oddly enough, they do one full heart of contact damage, despite Chargers and even Conjoined Spitties doing half heart damage.

Conjoined Spitty
Conjoined Spitties are very similar to Spitties, but they have 80% more health and have 2 heads, 1 added on the back of its body, so they shoot forward and backward simultaneously.

Tainted Spitty
Tainted Spitties are exclusive to the Ascent to. They are much larger and tankier versions of regular Spitties that also move and spit faster.

They shoot blood shots out of their backs and occasionally spit out a line full of shots. Upon death, they shoot out a ring of blood shots.

Trivia

 * Oddly enough, in the original Binding of Isaac, Spitties were misspelled as "spities" in the ending credits.
 * Tainted Spitties bear striking resemblance to the second phase of Rotgut, named Gus.