Thelazia callipaeda is a parasitic nematode, and the most common cause of thelaziasis (or eyeworm infestation) in humans, dogs and cats.

In distinguishing this species from other worms, they have a distinct buccal capsule and a cuticle with spaced transverse striations giving it a ridged appearance.

This species has been found in China, France, Germany, India, Indonesia, Italy, Japan, Korea, the Netherlands, Russia, Switzerland, Taiwan, Croatia and Thailand.

[9][10] The eggs of Thelazia callipaeda develop into first stage larvae (L1), in utero while the female is in the tissues in and around the eye of the definitive host.

The seasonal timing of L1 and L4 larvae in the lacrymal (tear) secretions of naturally infested dogs in Italy was found to coincide with the activity of the fly vectors.

[12] Symptoms of T. callipaeda infestation include conjunctivitis, excessive watering (lacrimation), visual impairment, and ulcers or scarring of the cornea.