These are liver flukes of domestic animals, but are remarkable for their larval adaptations to enhance transmission. Cercariae produced in terrestrial snails irritate the mantle cavity of their host and cause mucus secretion. Large numbers of cercariae accumulate in these "slime balls" and are expelled by the snail. The mucus helps protect the cercariae from desiccation, and also attracts ants to feed on it. The ant ingests a slime ball, freeing the cercariae, which use their oral stylet to penetrate the gut and enter the hemocoele. Most encyst as metacercariae, but a few migrate to the subesophageal ganglion of the ant and stimulate a behavioral change. The ant will climb to the top of grass blades in the evening and remain there overnight, unlike uninfected ants which return to their nests. Thus, when cattle or sheep are grazing in the evening they ingest infected ants.