 Most larvae, however, come in contact with the bonellin in the skin of an adult female—its body or its roving, bonellin-rich proboscis—and are masculinised by this exposure.The chemical causes these larvae to develop into the tiny males, which cling to the female's body or are sucked inside it by the feeding tube, to spend the remainder of their lives inside her genital sac, producing sperm to fertilize her eggs, reliant on her for all other needs.The sex of a green spoonworm is thus determined by external, environmental factors (the presence or absence of bonellin), not by internal, genetic factors (chromosomes), as is the case with most other sexually-differentiated organisms.