March 30, 2022. Skylar and colleagues from Virginia Tech and Radford University published a new paper in Proceedings of the Royal Society B. They found that even though two host species are abundant and heavily infected with a worm symbiont in the wild, there is almost no interspecific transmission between the two host species. They used laboratory experiments to figure out why: the two host species often contact, but the symbionts have strong preferences for their current host species and rarely switch hosts during interspecific contacts. This was an unexpected barrier to transmission that might occur in many other host–symbiont systems. You can read the open access paper here.