Great Gordian knots:: sex ratio and sexual size dimorphism in aggregations of horsehair worms (Gordias difficilis)

Large knots (>100 individuals) of adult horsehair worms (Gordius difficilis) were collected in several spring-fed habitats in Wisconsin and Minnesota. These aggregations were dominated numerically by males. Although distributions of length and diameter of males and females overlapped, females tended to be significantly longer and wider than males. Moreover, at any given length, females were wider than males. These findings confirm and add statistical support to previously published reports.