This paper examines the impact of an industrial point-source atmospheric emission on the feeding of early life stages of a terrestrial invertebrate. Larvae of a bagworm moth, Luffia ferchaultella [Stephens], were fed terrestrial epiphytic algae (Desmococcus viridis [Menegh]) collected from five sites located along a 16 km transect around the Avonmouth zinc smelter. After 10 days of exposure symptoms of lethal and sublethal toxicity (mortality and paralysis) were observed. Reductions in the amount of faecal material (frass) produced were also identified, and these correlated with distance downwind of the smelter. The elevated concentrations of lead, mercury, arsenic, antimony, copper, cadmium, lead and nickel present in the algae could account for these symptoms of toxicity. Similar symptoms were observed when larvae were fed algae spiked with inorganic mercury. These results are consistent with other studies of soil toxicity conducted around the Avonmouth smelter. However, the current study suggests that the impacted area exceeds this 16 km transect and demonstrates the value of bagmoth larvae as sensitive biomonitors of metallic atmospheric pollutants above the rhizosphere.