Japanese Name: Hachijo-Kokuwagata (Hachijo Island subspecies of Dorcus rectus)
Scientific Name: Dorcus rectus miekoae (Yosida, 1991)
Distribution: Hachijo Island
Wild Rarity: Rare ★★★★☆☆
Size: ♂ 23–49mm / ♀ 23–28mm
Breeding Record: 51.2mm (2004) – BE-KUWA, as of 2021
Wild Record: 49mm – BE-KUWA, as of 2021

Breeding Difficulty: Normal ★★★☆☆☆☆
Breeding Temperature: 10–28°C (Reference: Hachijo Island climate)
Adult Lifespan: Over 1 year
Larval Duration: Around 4–10 months

Notes

 

 

Among Dorcus rectus populations, those inhabiting Hachijo Island are classified as the subspecies Hachijo-Kokuwagata.
Their characteristics include a stronger gloss and slight reddish tint, and the male mandibles appear thinner compared to mainland Japanese Dorcus rectus.
They also tend to be smaller overall—typically 3–5mm shorter than mainland individuals.

Ecology and breeding methods are the same as those of mainland Kokuwagata.
They lay eggs in soft oviposition wood, and larvae grow well in either fermented substrate or mushroom-spawn substrate (kinshi).
Personally, I find that kinshi tends to yield larger individuals.
Recently, the population on Hachijo Island is said to be increasing.

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Breeding Log

Around May–June 2021: Acquisition & Oviposition Setup

I obtained wild-caught individuals from the Mine area of Hachijo Island.

Since they were already active, I prepared several simple oviposition setups by placing a small amount of fermented substrate and one piece of oviposition wood in clear sliders, and kept one pair together to observe.
Surprisingly, the oviposition switch did not activate in May. Actual egg-laying seemed to begin around June–July.

2021/9/3 Kinshi Bottle Introduction

I broke apart the oviposition wood, collected 1st–2nd instar larvae, and placed them into 800ml kinshi bottles.
Since I didn’t have enough bottles, I prepared some with one larva per bottle and others with two larvae per bottle.
Extra larvae were kept in 200ml pudding cups with fermented substrate.

2022/4/5 Partial Kinshi Excavation

Some neglected bottles developed a massive outbreak of nematodes, so I performed an emergency excavation.

— 800ml bottle filled with nematodes
— Pupae moved into improvised artificial pupal chambers

Some had already emerged as adults, but about half were still pupae.
I prepared improvised artificial pupal chambers by packing wet tissues into 200ml pudding cups.
The bottles not excavated also contained individuals either pupating or already emerging, so I plan to check them later.

2022/4/19 Emergence

Most individuals had emerged, so I dug them out and summarized the data.

● 800ml, 2 larvae per bottle

Males: 49mm, 46mm, 46mm, 46mm, 45mm, 44mm, 40mm, 40mm
Females: 31mm, 30mm, 30mm, 29mm, 29mm, 29mm, 28mm × 7

● 800ml, 1 larva per bottle

Males: 49mm, 49mm, 46mm
Females: 33mm, 30mm, 30mm, 30mm

Kinshi-raised individuals emerged at 40–49mm for males and 28–33mm for females.
As expected, the one-larva-per-800ml bottles produced noticeably larger specimens.
Among them, the 33mm female stood out as unusually large—possibly near record size.

The individuals collected at the pupal stage earlier also emerged healthily.

This time, the largest male was 2mm smaller than the record, but with a mid-stage kinshi replacement or better kinshi maintenance, larger results might have been possible.

For the next generation, I plan to start again with 1 larva per 800ml bottle and raise the minimum winter temperature to keep them more active.
They were kept in a slightly cold environment over winter, so they took long to grow but didn’t feed enough, and the kinshi degraded over time.

There were also many individuals raised in 200ml pudding cups, but I will omit them here.