Courtship occurs in two phases. During the aerial phase, a male pursues and often forces a female to the ground. During the ground phase, the butterflies copulate and remain attached for about 30 to 60 minutes.  Only 30% of mating attempts end in copulation, suggesting that females may be able to avoid mating, though some have more success than others.   During copulation, a male transfers his spermatophore to a female. Along with sperm , the spermatophore provides a female with nutrition, which aids her in egg laying. An increase in spermatophore size increases the fecundity of female monarchs. Males that produce larger spermatophores also fertilize more females' eggs.