A mind-controlling parasite is infecting brains and forcing its hosts to throw themselves into the nearest body of water to drown.

It is not the stuff of science fiction, but it is the reality for many of New Zealand’s humble earwigs. 

In a new study published by the University of Otago, scientists have uncovered the reasons behind the bizarre behaviour. 

Published in Proceedings of the Royal Society B, the study decoded the genetic crosstalk between the European earwig and the mind-controlling parasitic worm, mermithid nematode. 

Senior author and University of Otago anatomy researcher Prof Neil Gemmell said once the worms were fully developed in the earwig, they forced the bug to seek water so they could  reproduce. 

Once water was found, the earwig drowned and the parasite fulfilled its goal. 

He said it was classic host manipulation, but was previously poorly understood. 

“Our findings reveal how parasites and hosts interact at the genetic level to produce these dramatic behavioural changes.” 

They found thousands of genes were changing in both the earwig and worm during the manipulation — earwigs showed increased activity in sensory and signalling pathways, while parasites activated genes involved in transport and secretion.

They shared a common regulatory signal, which suggested the molecular changes were co-ordinated. 

Things for the earwig remained fairly business-as-usual until the worm wanted to go for a swim. 

New Zealand Institute for Bioeconomy Science co-author Dr Eddy Dowle studies the similar water-seeking behaviour in New Zealand’s native hairworm-wētā system.

‘’Host manipulation provides a remarkable opportunity to understand how one organism can influence the behaviour of another, and future comparisons of these systems may help us uncover common mechanisms that parasites use to manipulate their hosts.” —  Allied Media