At least 680,000 beetles were imported into Japan last year, according to a study recently released by Traffic East Asia-Japan, a Tokyo-based group monitoring trade in wildlife.
About 319,000 rhinoceros and 364,000 stag beetles were imported, according to the study, which was based on records by plant protection offices nationwide.
Based on the findings, Traffic's Japan office says it has urged the Environment and agriculture ministries to create measures to address the problem of foreign species, which can threaten native beetles if they escape or are set free.
The popularity of beetle breeding has increased in recent years. In addition to crossbreeding of native and foreign species, experts say territorial disputes also occur between bigger alien beetles and native ones.
Separately, a survey of 40 pet shops in the Kanto and Kansai areas shows that 62 beetle species from 25 countries had been sold, according to Traffic East Asia-Japan.
They include ones banned for import. Others originated from countries that ban the export of wild species, including India, Bhutan, Nepal and the Philippines, it said.
Since 1999, 34 foreign beetle species have been found in Japan's urban areas and forests.