Jennifer Harbster writes: “The last time Periodical Cicadas Brood XIX (13 year) and Brood XIII (17 year) emerged at the same time was in 1803, when Thomas Jefferson was president of the US. Usually only one brood will emerge at the same time, but some years, like 2024, two different broods will co-emerge. The Science Section of the Library of Congress has created ‘Periodical Cicadas: A Resource Guide’ to celebrate the double emergence of periodical cicadas this summer.”