Ichneumon wasp (Ichneumonidae: Cryptinae) from Wisconsin.
Most Pseudomyrmex ants (like this one from Costa Rica) are twig nesters, seeking refuge in the hollow stems of a variety of plants. Some have even evolved obligate mutualisms with Acacia trees, defending them from competitors and herbivores in exchange for nectar and protein-rich excretions called Beltian bodies.
A pair of Pseudomyrmex ants on a bullthorn Acacia from Belize. These organisms have a mutualistic, or mutually beneficial relationship. The acacia provides shelter (via hollow spines) and food (by producing nectar and lipid-rich excretions called Beltian bodies) for the ants, and in return, the ant colony protects the tree from herbivores. Amazingly, some species even go so far as to attack and kill surrounding plants to decrease competition for the acacia.
