Social media have long been considered a venue in which conspiracy theories originate and spread. It has been no different during COVID-19. However, understanding who spreads conspiracy theories by sharing them on social media, and why, has been underexplored, especially in a cross-national context. The global nature of the novel coronavirus pandemic presents a unique opportunity to understand the exposure and sharing of the same COVID-19 related conspiracies across multiple countries. We rely on large, nationally representative surveys conducted in July of 2020 in the United States, United Kingdom, Canada, Australia, and New Zealand, to begin to understand who shares conspiracies on social media and what motivates them. We find that Americans are no more likely to encounter prominent COVID-19 conspiracies on social media but are considerably more likely to subsequently share them. In all countries, trust in information from social media predicts conspiracy theory sharing, while in the US politics plays a unique role Our results make clear that American behavior on social media has the potential to poison online public discourse globally.