We studied the adult behavior, oviposition, and larval and pupal development of Hoplia philanthus Füessly (Scarabaeidae: Melolonthinae) in the field and laboratory in Belgium. Adult emergence was observed in the first week of June 2000, 2001, and 2002, peaked ≈2 wk later, and continued until the last week of the month. The average sex ratio of emerging adults was 1.3:1 (male and females) during the collection period. Adults were observed feeding mainly on leaves of Betula utilis variety jacquemontii (B. u. Doorenbos) and Carpinus betulus L. During the day, H. philanthus adults were most active at 1400 hours (GMT 1.00). Oviposition started in the last week of June and lasted until the end of July. Each female deposited ≈25–40 white eggs at a depth of 10–15 cm in soil. Eggs hatched 28 ± 5 d after being laid at an average monthly soil temperature of 18.1°C. Three larval instars could be discerned by head capsule width; all larval instars fed on grass roots. The first-instar larvae were found in the last week of July 2000; second instars appeared mostly in the second week of September 2000 and could be found until May 2001. Third instars were found from the second week of June 2001 until April 2002. Pupae could be found from the first week of May until the end of the month. The duration of the pupal stage was 28 ± 5 d at an average monthly soil temperature of 16.5°C. According to these observations, H. philanthus has a 2-yr life cycle.