The acorn moth, Blastobasis glandulella (Riley, 1871) (Lepidoptera: Blastobasidae) is native to the USA. It was recorded in Europe at the beginning of the 1980s and in western Ukraine in 2009 as Blastobasis huemeri. This insect was often found in acorns already infested by weevils or damaged by rodents and was not considered a serious pest. In 2021, a large population of the acorn moth was recorded in oak plantations in Poland. Considering this information, we asked the foresters and amateurs to send samples of acorns, chestnuts, walnuts, and other hard-shelled fruits from various regions to the Ukrainian Research Institute of Forestry & Forest Melioration to study the host range, prevalence, rate of infestation, phenology of acorn moth, and its associations with other fruit pests. The fruits collected on different dates and places were dissected. Part of the samples were reared in the laboratory to obtain pupae and adults. The presence of B. glandulella was confirmed in 14 regions of Ukraine. It infests the fruits of Quercus sp., Aesculus sp., and Juglans sp. The infestation rate depends on the region, fruit crop, weather, and forest structure and exceeds 60 % of fruits in some samples. The development of all stages is very extended: the moths swarm from April to mid-September. The early swarming moths can be the first invaders in developing fruits. After consuming the cotyledons, the larva crawls to another fruit in the crown or on the forest litter, sometimes doing it several times before pupation. In August, the larva of B. glandulella may be found in prematurely fallen fruits with other carpophagous insects, their excrements, or molting skins. The larva of the last instar overwinters. In spring depending on the instar, it crawls to another fruit or pupates inside or outside the fruit, or on the forest litter.