In spite of the vast distribution and considerable impact on human and animal health of Ascaris suum and A. lumbricoides, little is known of the sexual biology and reproductive capacity of these intestinal nematodes. By oral transfer of adult female worms to previously parasite-naive pigs we show that in the absence of males the egg production ceases after 2–3 weeks. Such females readily resume egg production a few days after oral transfer of male worms. These observations throw light on an important aspect of Ascaris biology, but also pave the way for possible experimental interbreeding between the human and pig Ascaris species.