Japanese Giant Stag Beetle Breeding Guide — Egg-Laying Setup & Bloodline Management

The Japanese stag beetle (Ookuwa) is the most popular among Japanese stag beetle species and is relatively easy to breed. Breeding aimed at producing large specimens is deep and rewarding, with bloodline management and improvements in rearing techniques being one of the pleasures. Here we explain the basic breeding methods for the Japanese stag beetle.

Pairing (Mating) Methods

Breeding requires mature males and females. Japanese stag beetles are considered mature when they have been 3 months or more since emergence and have been feeding for at least 2 months after starting to eat. Spring to early summer after overwintering is the optimal time for pairing. There are two methods: hand pairing and cohabitation pairing. Hand pairing involves directly bringing a male and female together in front of the keeper and confirming mating. The advantage is that you can visually confirm mating, but monitoring is necessary to prevent the male from attacking the female. Cohabitation pairing involves keeping a male and female in the same case for about a week, allowing natural mating to occur. To prevent accidents with the female being pinched by the male, set up multiple hiding spots in the case and provide plenty of food.

How to Set Up a Spawning Box

After confirming mating, introduce the female into the spawning box. Since Japanese stag beetles are wood-spawning species, wood logs (decaying logs of Japanese oak or similar hardwoods) are necessary. After purchase, soak the spawning wood in a bucket of water for half a day to a full day, then dry it in the shade for half a day before use. Pack wood chip mulch firmly on the bottom of the breeding case (medium to large size) about 3 cm deep, place the spawning wood on top, and bury the surrounding area with mulch. Cover the spawning wood with mulch so that the upper part is slightly exposed. Using 2 logs tends to increase the number of eggs laid. The optimal temperature is 23–25°C, and be careful not to run out of jelly food. The spawning period is typically 1 to 1.5 months after introducing the female. If there are signs of the female scraping the wood, it is likely that spawning is occurring.

Excavation and Care of First-instar Larvae

About 1 month after removing the female from the spawning box, excavation (extracting larvae from the spawning wood) is performed. Be careful not to damage the eggs if done too early. Carefully split the spawning wood by hand and remove the larvae using a fine-tipped tool such as a flathead screwdriver without injuring them. If eggs are found, move them to a small container with mulch and wait for them to hatch. First-instar larvae are placed individually in fungal culture or mulch packed in small cups (about 200 ml). Fungal culture bottles are most effective for rearing Japanese stag beetle larvae and are essential for growing large specimens. When placing first-instar larvae into the fungal culture, make a hole with a wooden stick, gently place them in, and lightly cover with mulch from above.

Basics of Bloodline Management

Bloodline management is important for consistently producing large specimens. Keep records of emerged specimens (body length, weight, emergence date, parent information) and create a management ledger. To avoid inbreeding within the same bloodline, it is recommended to maintain lines from different bloodlines. However, in Japanese stag beetle breeding, intentional inbreeding (line breeding) is sometimes practiced to fix desirable traits. In that case, keep track of the number of generations and watch out for the negative effects of extreme inbreeding (incomplete emergence, dwarfism, reduced hatching rate). Famous bloodlines include the Nose YG bloodline and the Kurume bloodline, each with different characteristics.

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If you aim to produce large Japanese stag beetle specimens through breeding, the bloodline of the parent insects as your starting point is extremely important. At Brichoku, you can directly purchase specimens with clear bloodline information from breeders with a proven track record of producing large bloodlines. You can also get information about the size of the parent insects, number of generations, bloodline name, and the type of fungal culture used, which you can apply to your own breeding plans. Practical advice from breeders, such as breeding tips and how to choose fungal culture bottles, will also be of great value.