Females of giant water bug species glue eggs to their mates' backs via bodily secretions that act as a type of waterproof glue.
“Using bodily secretions, the female [giant water bug] glues the eggs to her mate’s back.” (Crump 2005:52)
Crump, M. 2005. Headless Males Make Great Lovers & Other Unusual Natural Histories. University of Chicago Press, Chicago, IL. 199 pp.