Earwigs are small insects known for their distinctive pincers at the end of their bodies. While they generally avoid open water, they are often found in damp environments. However, a recent study has shown that European earwigs infected with a parasitic roundworm called Mermis nigrescens behave differently, often heading toward open water. Scientists from the University of Otago in New Zealand, the New Zealand Institute for Bioeconomy Science Limited, the University of British Columbia, and Brown University explored the genetic reasons behind this unusual behavior. Their research, published in Proceedings of the Royal Society B: Biological Sciences, reveals that both the earwigs and the parasites undergo significant changes in gene activity. The study was inspired by observations of native New Zealand wētā, large ground insects that were found drowned in puddles with long hairworms emerging from their bodies. This led researchers to investigate whether a similar phenomenon occurred with European earwigs. They collected earwigs at various stages of infection with Mermis nigrescens and compared them with uninfected individuals. Using a technique called RNA sequencing, they analyzed the expression of genes in both the host insects and the parasites. The researchers discovered that thousands of genes in both the earwigs and the roundworms changed activity levels depending on the stage of infection. They identified activity in 12,876 earwig genes and 9,722 roundworm genes. Among these, 673 earwig genes and 2,672 worm genes became more active, while 593 earwig genes and 2,293 worm genes showed reduced activity. These findings suggest that the earwigs increase activity in genes related to sensory perception and signaling, while the parasites activate genes involved in transport and secretion. This indicates a complex and coordinated interaction between the host and the parasite at the molecular level. This study offers the first detailed genetic view of how a parasitic nematode influences an insect's behavior. It suggests that the parasite does not take over the host's behavior through brute force but instead uses subtle, coordinated molecular changes to guide it. This discovery could lead to more research on how parasites manipulate animal behavior, providing deeper understanding of the interactions between hosts and their parasites. Neil J. Gemmell, one of the senior authors, noted that the team is interested in continuing this line of research, although securing funding for such studies remains a challenge.