When the hairworm reaches maturity, it induces the host to enter water (including ponds and rivers), where the hairworm breeds, thus completing its life cycle.

The hairworm parasite lives inside the body of an insect host (such as mantids and crickets) that typically inhabits forests and grasslands.

These research findings were published in the American scientific journal Current Biology on June 21, 2021. Chiu Ming-Chung (National Changhua University of Education, Taiwan). This discovery was made by an international research group consisting of Graduate student OBAYASHI Nasono, Associate Professor Sakura Midori and Associate Professor Sato Takuya of Kobe University's Graduate School of Science, Associate Professor Iwatani Yasushi (Faculty of Science and Technology, Hirosaki University), Professor Tamotsu Satoshi (KYOUSEI Science Center for Life and Nature, Nara Women's University) and Dr. In a world-first, these research results demonstrate that parasites can manipulate the host's specific light perception system to their advantage, causing the host to behave in an abnormal manner.

Researchers have revealed that praying mantis (mantids) infected with parasitic hairworms are attracted to horizontally polarized light that is strongly reflected off the surface of water, which causes them to enter the water. Once the mantid is in the water, the hairworm escapes back into the aquatic environment to reproduce, and its lifecycle ends. If the aquatic insect is consumed by a mantid, the hairworm grows inside the mantid’s body until it reaches maturity and causes its host to enter the water. After the aquatic insect has grown wings, the hairworm is transported from an aquatic environment to a terrestrial environment. After hatching in the water, hairworm larvae parasitize aquatic insects and form a cyst in the hosts’ body cavity. Figure 1: The life cycle of the hairworm.

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