Ghost silverfish, an invasive insect that feeds on paper, have been found in facilities such as museums and libraries in 19 prefectures, including Tokyo.
The insect reproduces parthenogenetically -- females lay eggs that develop into offspring without being fertilized -- and their population can increase quickly. This makes extermination very challenging once the insect has a foothold in an area.
The Tokyo National Research Institute for Cultural Properties is calling for facilities to deal with the pests at an early stage.
Ghost silverfish were discovered in Sri Lanka in 1910. An adult has a body about 1 centimeter long. The insect nibbles at the surface of paper, and is therefore considered a threat toward items of historical significance, such as ancient documents, byobu screens and scrolls.
The insect was found in Japan for the first time in 2022, and was present in museums, historical archives and libraries across five prefectures, including Tokyo, Hokkaido and Fukuoka.
Since the insect's biology was not well understood, the Tokyo institute conducted investigations. It discovered the insects were female and parthenogenetic.
This capacity for solo reproduction means that complete eradication is required in the event of an infestation. One ghost silverfish can lead to a population of 20,000 in three years. The insect's reproductive power is far stronger than that of ordinary silverfish, which reproduce sexually.
The institute has been able to confirm that ghost silverfish could be eradicated in temperatures of 10 C or below or in humidities of 43% or lower. However, it thrives in facilities like museums and libraries where the temperature and humidity are kept at certain levels to protect the books and other cultural properties.
The spread of ghost silverfish to 19 prefectures, presumably being transported unknowingly in documents and packing material, was reported by the institute.
No damage to cultural properties has been reported yet. However, the institute is calling for measures to be taken against ghost silverfish. Specifically, facilities should: Keep documents in steel or plastic cases, rather than cardboard boxes, where ghost silverfish can easily reproduce; spray pesticide on walls; clean frequently; and lay poison bait.
This month, the institute started providing museums and other facilities where the insect has been spotted with poison bait kits.
"Once ghost silverfish have gained a foothold, it becomes extremely difficult to get rid of them," said Yoshinori Sato, the head of the institute's biological science section. "We'd like to stop their rise before they spread nationwide."