Rhaetulus crenatus recticornis – from…. Japan!

Rhaetulus crenatus recticornis male, from Amami Oshima Japan

Long time back, when I was still studying, I somehow had the goal to have a specimen collection of all Taiwanese and Japanese Lucanidae. I got quite far, what is still missing are small species like the different Aegus subspecies of Japan, and some Platycerus, and Rhaetulus crenatus recticornis. It used to annoy me to no end that no one could ever provide me with one. Not that they are especially beautiful, especially if compared with the nominate Rhaetulus crenatus crenatus with its huge mandibles, but the grapes you cannot reach are always the sweetest. They are endemic to Amami Oshima Island, far away from the mainland, and that fact made them rare, as people will have to fly to the island to collect them. One more thing, these are often wrongly referred to as Rhaetulus recticornis. In fact you will find more images and websites if you look for this term.

Rhaetulus crenatus recticornis breeding pair, from Amami Oshima Japan

I think this feeling stayed with me, and when I got the opportunity to get five larvae of the species, I rejoiced. I got them in September last year, small L2. They went into 300ml containers filled with flake soil, which was kept on the slightly drier side. I did not often check them, and they seemed to be happy doing their thing. I noticed the first pupation and building of cocoon chambers in February, the first female hatched in March. Males hatched in April and May. I waited a few weeks after the males had hatched and then prepared to breeding containers. 22-litre boxes, filled with sawdust, compressed at the bottom 3cm, then pieces of white-rotten wood, harder and softer, and the whole thing topped off with more white-rotten sawdust. Regular maintenance included replacing the beetle jelly every few days and enjoy seeing the wood pieces being chewed into sawdust by the females. Rhaetulus crenatus recticornis were easy as they laid eggs into all wood pieces provided, and also some into the substrate. The beetles are still alive, but because I had noticed larvae on the container walls I decided to check the container, and collect all the larvae that are in the substrate. From both containers I collected 14 larvae, but there are many inside the wood pieces. I really do not like to break the wood pieces, as I often kill larvae accidentally, and overlook the small ones. So these went back into the container to be checked on another time.

Rhaetulus crenatus recticornis larva L3 , from Amami Oshima Japan

This is a good species and surprisingly easy to rear. They also grow fairly large on flake soil, which makes them a good beginners species. Yes, they are not very spectacular, but they are only occurring on one island, so let’s try to maintain them in captivity. And, once the imagines die, I finally, after 20 years of waiting am able to close that gap in my collection of Japanese Lucanidae!

Rhaetulus crenatus recticornis breeding pair, from Amami Oshima Japan

Rhaetulus crenatus recticornis male closeup