The genus Merodon Meigen, 1803 is one of the richest hoverfly genera, with around 180 species know species in the Palearctic region, with the highest species diversity recorded for the Mediterranean Basin. The larval biology of most Merodon species remain unknown, however, the development of all species which the preimaginal stages have been identified, occurs in bulbs of monocotyledonous plants of families Amaryllidaceae, Asparagaceae, Iridaceae and Liliaceae.

The genus is classified into more than 20 monophyletic species (Vujic et al., 2021) groups being Merodon triangulum Vujić, Radenković & Hurkmans, 2020, belongs to the constans group and the albifrons lineage. It is a European endemic species, known from north-eastern Italy, northern Austria, eastern Hungary, Slovenia, Croatia, Serbia, Montenegro, and North Macedonia. The aim of this paper is to present the first data about preimaginal morphology (both larva and pupa) of this species, described using both optical microscopy and scanning electron microscopy. The larval description was obtained from wild larval specimens collected in Petrovaradinski rid, Novi Sad, Serbia, collected in June 2020, feeding inside bulbs of Leucojum vernum L. 1753 (Amaryllidaceae).