In male spiders, genitalia, sexual behaviour and secondary sex morphology tend to diverge rapidly across species, presumably as a result of sexual selection. In the three Leucauge species for which pre- and copulatory courtship behaviour is known, females clamp the male chelicerae prior to and during copulation. This brings the basal segment of the male's chelicerae into contact with the anterior surface of the female's chelicerae. The basal segment of male's chelicerae has also morphological features such as sturdy, abundant setae which are thought to have evolved to stimulate females, as well as other morphological features whose specific function is yet unknown. We show here that in a fourth species, Leucauge sp., the female does not clamp the male's chelicerae; as expected, this absence is associated with a lack of secondary sexual differences in the male chelicerae.