Nestling mortality in the endangered and endemic Hihi, also called Stitchbird (Notiomystis cincta), was studied over the 2008–09 breeding season at Zealandia-Karori Sanctuary, Wellington, New Zealand. Histopathology showed traumatic ventriculitis in seven of 25 (28%) dead nestlings. Single or multiple granulomas centered on chitinous insect remnants were found lodged within the gizzard mucosa, muscle layers, and ventricular or intestinal serosa. The insect remnants were confirmed as bee or wasp stings (Hymenoptera) using light and electron microscopy. Bacteria or yeasts were also found in some granulomas, and death was due to bacterial septicemia in four cases. Endemic New Zealand birds are likely to lack evolutionary adaptations required to safely consume introduced honey bees (Apis mellifera) and vespulid wasps (Vespula germanica [German wasp], and Vespula vulgaris [common wasp]). However, these insects are attracted to feeding stations used to support translocated Hihi populations. As contact between bees, wasps, and the endemic fauna of New Zealand seems inevitable, it may be necessary to minimize the numbers of these introduced insects in areas set aside for ecologic restoration.