Eupatorus gracilicornis

Males use their horns in ritualized combat and pushing contests to gain access to mates or feeding sites; contests are typically non-lethal but determine dominance. Adults are largely nocturnal, commonly attracted to tree sap, fermenting fruit and lights, and are strong but relatively short-distance fliers.

Females lay eggs in decaying wood or organic soil; larvae are typical scarab “C-shaped” grubs that feed on rotten wood/substrate and undergo a long larval development (many months to over a year depending on conditions) before pupating and emerging as adults. Captive-breeding is practiced by hobbyists but can be challenging to complete reliably to successive generations.

Sexual dimorphism is strong — males bear the multi-horn arrangement while females are smaller and largely hornless. Body length commonly ranges from ~50 mm upward depending on locality and subspecies; the exoskeleton is thick and glossy, and the legs are adapted for digging and holding during fights. The horn morphology (one cephalic + paired pronotal processes) is diagnostic for the species.

Eupatorus gracilicornis was described by Arrow (1908) and belongs to the Dynastinae (rhinoceros beetles) common in Indo-China. Its known range includes parts of Southeast Asia — records come from southern China, Myanmar, Thailand, Laos, Vietnam, India (Assam) and Malaysia — with occurrences documented in museum and citizen-science databases.

The species is not widely assessed on a global IUCN Red List as a single entry, but local populations face pressure from habitat loss (deforestation, land conversion) and collection for the insect trade and local use (including as pet/fighting beetles in some areas). Protecting native forest and limiting overcollection are the main conservation priorities.