Background <p>Insects have evolved various antipredator defenses, some of which produce copious chemicals when threatened, such as ants, beetles, butterflies, moths, stick insects, and true bugs. The true bugs (Hemiptera: Heteroptera) are known for their foul odor, which comprises over 45,000 species of biologically and economically important insects. One key element to the success of heteropterans is the evolution of specialized defensive glands, specifically the metathoracic scent gland in adults and the dorsal abdominal scent glands in nymphs, a hallmark synapomorphy for the clade. Within Pentatomomorpha, the scent gland peritreme exhibits remarkable morphological diversity, yet its evolutionary origins and drivers remain poorly understood due to sparse fossil evidence of these delicate structures.</p> Results <p>We report a series of Mesozoic fossils with well-preserved scent gland anatomy, including the earliest evidence from the Jurassic (165 million years ago), revealing an ancestral auricle-type morphology. Ancestral-state reconstruction across 40 extant and fossil taxa confirms the auricle as the plesiomorphic condition for Pentatomomorpha. Fossil evidence demonstrates phenotypic diversification by the Early Cretaceous (~ 125&#xa0;Ma), with many peritreme types (auricle, spout, groove) emerging by the mid-Cretaceous. Developmental analyses of extant taxa show no pre-adult differentiation, indicating rapid peritreme formation during the final molt.</p> Conclusions <p>The scent gland peritreme evolved as a rapidly developing from a simple underdeveloped to auricle to five well-developed basic derived types in early Pentatomomorpha. Its subsequent diversification into specialized forms coincided with mid-Mesozoic habitat shifts and predator pressures, particularly during angiosperm proliferation. Convergent morphologies across lineages reflect shared ecological constraints and developmental plasticity.</p>