The Japanese rhinoceros beetle, Trypoxylus dichotomus, is one of the most widely kept beetle species in the hobby. In Japan they're called kabutomushi, they're sold in department stores during summer, and kids keep them the way British children once kept caterpillars. Males have a dramatic forked horn on the head and a smaller pronotal horn behind it. Females are hornless and slightly smaller.
They're a Dynastinae species (rhinoceros beetle subfamily) and a solid step up from flower beetles if you've already kept Pachnoda or similar. The care isn't dramatically harder, but the life cycle is longer and the larvae need more space and substrate.
A note on names
You'll see this species listed as both Trypoxylus dichotomus and Allomyrina dichotoma in hobbyist circles and on seller websites. Trypoxylus dichotomus is the current accepted name. Allomyrina dichotoma is the old name that's still widely used. They're the same beetle. Several subspecies exist across East Asia; the nominate form (T. dichotomus dichotomus) from Japan is the most commonly kept.
Adult care
Adults are large for a hobby beetle, typically 4-8cm in body length, with males at the upper end of that range thanks to the horns. They're nocturnal and crepuscular, meaning they're most active around dusk and through the night. During the day they tend to stay buried in substrate or tucked under bark.
House adults in a well-ventilated container with several centimetres of moist substrate (coco coir or a mix of coir and leaf litter works fine for adults), a piece of bark or cork for climbing, and food. A 10-15 litre container is reasonable for a pair.
Feed beetle jelly, ripe banana, or other soft fruit. Beetle jelly is the cleanest option and what most Japanese keepers use. Males and females both feed readily. Replace food every couple of days.
Adult lifespan is roughly two to four months. Males fight each other using their horns, flipping rivals off branches. It looks dramatic but rarely causes injuries. If you keep multiple males together in a small space, the weaker ones may get stressed and feed less. Keeping pairs or trios (one male, two females) tends to work better.
Breeding
Females need deep, moist fermented substrate to lay eggs. Fill the breeding enclosure with at least 15-20cm of firmly packed flake soil. The bottom third should be compressed quite hard; females prefer to lay eggs deep in dense substrate.
Keep the breeding setup at 22-26C. Mating happens naturally when you house adults together. Females will burrow deep to oviposit, and you can expect anywhere from 20 to 50 eggs from a well-fed female over her lifespan.
After the female has been laying for a few weeks (you can often tell because she spends long periods buried), remove the adults and leave the substrate undisturbed. Eggs hatch in two to four weeks.
Larval care
This is where T. dichotomus keeping diverges from sun beetles. The larval period is roughly 10-14 months, and the larvae get big. An L3 grub can weigh over 30-40 grams and reach 8-10cm in length. They need proportionally more substrate and larger containers.
Use good quality fermented hardwood flake soil. Substrate quality matters more here than with Pachnoda because the longer larval period means the grubs are relying on that substrate for over a year. Poor substrate doesn't just slow growth; it can kill larvae that would have been fine on better material.
Individual containers of 3-5 litres per larva work well. Fill with firmly packed flake soil and bury the larva just below the surface. It'll dig down immediately.
Top up or replace substrate every four to six weeks, or whenever you see that more than half the volume has been converted to frass. L3 larvae eat through substrate at a surprising rate. Some keepers go through several litres of flake soil per larva over the course of development.
Temperature during the larval stage should be 20-25C. Slightly cooler temperatures (18-22C) during winter can mimic the natural seasonal cycle and may contribute to larger adults, though this is debated. Don't let temperatures drop below 15C, and avoid sustained heat above 28C.
Pupation
When the L3 larva is fully grown, it stops feeding and its body may take on a yellowish tinge. It constructs a pupal cell, which in T. dichotomus is a large, smooth oval chamber. Because the larvae are big, the cells are proportionally big, and the container needs enough substrate depth for the larva to build one without hitting the bottom or sides.
Once the larva begins constructing its cell, do not disturb the container for at least six to eight weeks. The pupal stage itself lasts about three to four weeks, plus time for the newly eclosed adult to harden inside the cell before digging out.
If all goes well, you'll come back to your container one day and find a fully hardened adult beetle sitting on the surface, ready for its adult setup.
Common issues
Slow larval growth: Usually substrate quality. If you're using cheap or poorly fermented flake soil, larvae grow slowly and produce undersized adults. Good substrate makes a visible difference within weeks.
Larvae surfacing repeatedly: The substrate may be too wet, too dry, or of poor quality. Check moisture levels and consider swapping the substrate entirely.
Failed pupation: Almost always caused by disturbance or insufficient substrate depth. The pupal cell is fragile. Once a larva goes pre-pupal, leave it alone.
Small adults: Adult size in rhinoceros beetles is determined almost entirely during the larval stage. If your adults are undersized, the cause was in the larval care: substrate quality, container size, temperature, or a combination of those factors.
Is this species right for you?
If you've successfully reared a faster species through its full cycle and you're comfortable with flake soil preparation and larval care, T. dichotomus is a natural next step. The main thing it demands beyond what sun beetles need is patience. A year is a long time to wait for a beetle, and maintaining consistent conditions over that period takes some discipline. But when a big male finally surfaces with those forked horns, it's worth the wait.