The fitness benefits of copulation are evident, but copulation can also incur costs to participating individuals. Many insects copulate for prolonged periods of time during which the female carries or drags the male. This behavior could result in decreased mobility, which in turn might influence the copulating pair's ability to escape from predators and to forage or thermoregulate. Here, I tested how copulation influences movement speed in the common squash bug (Anasa tristis) by measuring average movement speed of unpaired individuals and copulating pairs in an arena trial. Copulating pairs moved significantly slower but, surprisingly, the degree of size disparity between male and female did not influence movement speed. These results suggest that copulation incurs a mobility cost in this species, with potential consequences for survival, but that it is unlikely that mobility costs during copulation lead to selection for smaller male size.