A stag beetle’s life: sex-related differences in daily activity and behavior of Lucanus cervus

The study of behavioural ecology of rare and elusive species can be challenging, but it is an important issue for monitoring populations in planning conservation actions. This is especially true for arboreal insects inhabiting old-growth forests, whose habits are scarcely known and rely on many anecdotal data, such as the stag beetle Lucanus cervus (Linnaeus, 1758). In order to gather information on daily activity and behaviour of this species, a radio-telemetry study was conducted in a relict broadleaf forest surrounded by intensively cultivated land in northern Italy. During 2014 and 2015, from May to July, 55 stag beetles (34 males, 21 females) were radio-tagged. Most of them were caught with the aid of an entomological hand net, but nine of them were captured by emergence traps set up on deadwood. Visual contact analysis confirmed that stag beetle males were less elusive than females. Males were more frequently radio-tracked in flight, females mostly underground and in proximity of deadwood. Males were mostly observed flying at sunset, and resting or walking on standing trees during the day. The combination of air temperature and humidity determined the optimal weather conditions for male flights (temperature range: 20.7–26 °C, humidity range: 65.5–78.3%). Flying at sunset, mostly performed by males, significantly increased the detectability of the species and supported the selection of the ‘transect walk at dusk’ as the best monitoring method for the stag beetle.