Microplastic pollution is a pressing global concern, yet its immunotoxicological impacts on invertebrates remain poorly understood. The Black Soldier Fly (Hermetia illucens) larva has gained attention for its role in waste management and potential bioremediation, making it essential to evaluate its interactions with microplastics. In this study, fluorescent carboxylate-modified polystyrene microbeads were directly injected into the hemocoel of larvae to bypass gut-associated variables and investigate systemic immune responses. Experimental groups were analyzed at multiple time points (1 h, 6 h, 24 h, 48 h, and 7 days) using histopathology, cytology, and confocal laser scanning microscopy. Results confirmed the persistence and systemic distribution of microplastics in hemolymph and tissues, with hemocytes exhibiting active phagocytosis of particles. Microplastics were retained within tissues for up to seven days, indicating long-term sequestration. Histological observations further highlighted their close association with metabolically active organs such as the fat body and Malpighian tubules, suggesting possible effects on detoxification and metabolism. These findings demonstrate that microplastics elicit measurable immune responses and are subject to cellular uptake and retention in insect larvae. The study provides novel insights into the immunological and histopathological consequences of microplastic contamination in H. illucens larvae, with implications for their safe use in bioconversion and bioremediation applications.