【23mm】Specimen of a type of darkling beetle: Tribolium castaneum (Red Flour Beetle) / Tribolium destructor (Black Flour Beetle) / Tenebrionidae

Scientific Name: Passalidae sp.

Passalid beetles (Kuromushi) are a family of beetles belonging to the order Coleoptera. They are classified under the superfamily Scarabaeoidea and are considered closely related to stag beetles (Lucanidae). They are known to live in colonies within decaying wood, where adult parents care for their larvae, a behavior similar to that observed in the genus *Nipponolucanus* of stag beetles.

Nearly 600 species of passalid beetles have been discovered worldwide, with a wide distribution in tropical regions. In Japan, the endemic species *Cylindrocaulus patalis* can be found in mountainous areas west of Shikoku.

Passalid beetles exhibit a unique lifestyle, characterized by monogamy, which is rare among insects, and parental care of larvae. They live by digging tunnels within decaying wood, and both larvae and adults feed on this wood. The mandibles of the larvae are weaker compared to those of stag beetle larvae, making them unable to chew and consume wood on their own. Therefore, adult parents chew the wood, creating wood chips that they feed to the larvae. The number of larvae is small, typically no more than 10 even in the most populous species, but this is compensated by the continuous rearing of new larvae over a long period. The most extreme example is the Japanese species *Cylindrocaulus patalis*, which usually raises only one or at most two larvae at a time. The third instar is the final larval stage, and the larval period lasts about two months, which is significantly shorter than that of stag beetles or scarab beetles.

Newly emerged adult beetles have thin and soft exoskeletons and continue to grow by consuming wood chips within the tunnels. It takes two to three months for their exoskeletons to fully harden, a period that is exceptionally long, in contrast to the larval stage. During this time, their body weight increases about threefold compared to immediately after emergence. Only then do they leave the tunnels to begin a new life in a different location. It is known that during this period, they assist in caring for their younger siblings. This phenomenon closely resembles what is called helper behavior observed in birds and mammals, and in this way, the life of passalid beetles remarkably resembles human life.

Please note that we cannot guarantee against grade reduction due to shipping.
We will ship a specimen from Java, Indonesia. My measurement of the head-body length was 23mm.