Technical Abstract: Most contemporary research into aging is driven by interest in the human aging process and in interventions that attenuate the normal and pathophysiological effects of aging, or senescence. Operationally, senescence is the progressive, inevitable breakdown of the organism. Among the changes associated with senescence is the diminished capacity of the immune systems and reactions to challenge, known as immunosenescence. Senescence and age-related immunosenescence has been recorded in several invertebrates, including insects. Two invertebrates, the worm, Caenorhabditis elegans, and the fruit fly, Drosophila melanogaster, are model organisms for research into mechanisms of senescence and of prolonged life spans. In this essay, I will treat some of the available information on immunosenescence in invertebrates. The purpose is to move away from trying to understand human senescence and toward generating new ideas around the application of research into invertebrate immunosenescence to contemporary and emerging problems in aquatic and terrestrial agriculture. I cover mechanisms of senescence, beginning with the original idea of increasing oxidative damage and moving to more recent views. I provide a thumb-nail sketch of insect immunity as a model for the generality of complex invertebrates, then discuss selected examples of immunosenescence in invertebrates. In some instances, changes that look like immunosenescence may be physiological resource trade-offs and I highlight a few examples. Finally, I complete the essay with a few remarks on the potential practical significance of research to understand immunosenescence in invertebrates.