Dicrocoelium dendriticum

Abstract

Dicrocoelium dendriticum, the lancet fluke, dwells in the bile ducts of herbivorous animals. If ingested by certain terrestrial snails, the parasite eggs release a larva (‘miracidium’) that develops into asexually reproducing sporocysts. They then produce cercariae, which are embedded in tough mucus and expelled in packets. When Formica ants feed on these mucus balls, the cercariae penetrate into their body cavity. Nearly all cercariae encyst in the ant’s abdomen and develop into infective metacercariae. Yet, one larva settles in a specific region of the ant’s brain without forming a cyst wall. Once the metacercariae are mature, infected ants attach themselves to the foliage of plants by their mandibles in the evening. Attachment ceases only in the morning with rising temperature. This behavior exposes the infected ants to grazing herbivores and channels the encysted metacercariae to their final host, while the ‘brain worm’, without a cyst wall, does not survive the process of digestion.