Ghost Silverfish Reach 19 Japanese Prefectures, Putting Museums and Archives on Alert

A tiny insect spreads through Japan's collections

Ghost silverfish had been detected in 19 Japanese prefectures by the end of September 2025, just three years after the species was first confirmed in the country. The Tokyo National Research Institute for Cultural Properties has recorded its appearance in a growing number of public institutions, stretching from Hokkaido to the Kyushu region.

The pale insect is about one centimeter long as an adult, but its appetite for paper and glue makes it a concern for museums, libraries and archives. It can feed quietly on books, documents and other cultural holdings while hiding in cracks, behind baseboards and beneath floors. Early damage may resemble ordinary aging or wear from handling, allowing an infestation to grow before staff recognize it.

Researchers believe the movement of documents, packaged materials and collection items between facilities has helped the insect travel long distances. Its ability to reproduce without males adds to the concern: a single egg transported with a crate of books or a newly acquired folder could start a population in another building.

Sato Yoshinori, a senior official at the institute, has warned that the species is spreading faster than expected given its strong reproductive power. The institute is preparing a dedicated information website and can provide sticky monitoring traps and bait containing repellents free of charge to facilities where the pest has been confirmed.

As of November 5, 2025, no launch date has been given for the planned website. Institutions are being urged to focus on preventing entry, inspecting incoming materials and detecting small populations before they become established. Room temperature and moderate humidity can suit the insect, so ordinary indoor conditions may provide a place where it survives and reproduces.

Museums and archives face a particular challenge because their storage rooms bring large quantities of paper and textiles together. Keeping those holdings safe requires attention both to the objects themselves and to the routes through which insects can arrive.

How to recognize the ghost silverfish

Ctenolepisma calvum, commonly called the ghost silverfish, is a slender insect whose color ranges from pale gray to off white. Its flattened body narrows toward three filaments resembling tails, and its antennae are nearly as long as its body. It avoids light and moves quickly when disturbed.

Wall cavities, floor cracks and the spaces behind baseboards provide hiding places. These sheltered areas help explain why routine cleaning may miss an insect that is active nearby. Ghost silverfish belong to the same ancient lineage as the familiar silverfish and firebrat.

Several similar species can live in homes and museums, making identification difficult. The common silverfish generally looks more silvery. Ctenolepisma longicaudata, often called the gray silverfish, is usually darker and slightly larger.

Professionals use microscopic features and identification keys to confirm which species they have found. DNA barcoding, a method of identifying organisms through selected parts of their genetic material, has also supported findings that many ghost silverfish populations around the world are closely related. Correct identification helps researchers track its spread and assess the risk to collections.

How the insect reached 19 prefectures

Japan's first domestic records appeared in 2022, when captures were reported in a small number of prefectures. By late September 2025, researchers associated with the Tokyo National Research Institute for Cultural Properties had logged detections in 19, including Hokkaido and several prefectures in Kyushu.

The distance between those locations points to jumps through transport rather than a slow spread from one neighboring area to another. Loans between institutions, requests for copying documents and redistribution of stored materials all create opportunities for insects to travel.

Private shipments can provide routes as well. Cardboard, tissue papers, sanitary products and other packaged goods can shelter eggs or young insects. Tiny eggs and lightweight insects can survive ordinary shipping because conditions inside parcels often resemble the indoor environments in which the species thrives.

The recorded history spans more than a century:

• 1910: The species was first described from Sri Lanka.
• The two decades before November 2025: Records showed rapid expansion inside buildings across Europe, parts of the Americas and Asia.
• 2022: Ghost silverfish were first confirmed in Japan, with captures in a small number of prefectures.
• By the end of September 2025: Japanese detections had reached 19 prefectures.

Why paper collections are vulnerable

Ghost silverfish eat carbohydrates in paper fibers, book bindings, pastes made with starch and certain adhesives. They can also graze on labels, photographs and wallpaper. Feeding may leave shallow scrapes on a surface, irregular holes along an edge or loose paper layers where glue has been eaten.

Archives and collection stores concentrate potential food in a limited space. Where monitoring falls behind, that concentration can support larger insect populations. Climate control aimed at human comfort, particularly warmer stacks during summer, may also favor faster development.

Established insects can persist for years in hidden spaces and beneath floors. Their presence may escape notice even in rooms that look clean, because the first signs of feeding can blend into earlier damage or the effects of age.

Staff awareness and prompt reporting are therefore central to protection. Routine inspections give institutions a chance to identify activity before a full infestation response becomes necessary. A damaged label, a pale scrape on paper or an insect caught near shelving can help direct a closer search.

Why one egg can start a population

Researchers have found only females in multiple Japanese populations. These insects reproduce through parthenogenesis, meaning offspring develop without mating. A female does not need to find a male before producing the next generation, which helps explain the concern about even a single transported egg.

Laboratory observations at room temperature show egg laying from spring through late autumn, with a peak in early June. Eggs typically hatch within two months. Females can lay ten or more eggs at a time and may lay more than once a year.

Young insects grow through a series of molts, shedding their outer covering as they develop. Sexual maturity arrives around the tenth or eleventh molt, often within a year. Survival is high in the early stages of life and then declines slowly during later molts.

Temperature changes the pace of development. Cooler conditions lengthen the process, while warmer rooms speed it up. The species tolerates a range of temperatures but tends to flourish in climates typical of buildings.

Food flexibility also helps it survive. Tests have recorded feeding on tissues, protein powders, soy products and even dead insects, alongside paper and glue. Removing human food crumbs alone may therefore leave other food available in storage rooms and hidden spaces.

Where to look and what to record

Storage rooms, areas beneath shelving, baseboards, electrical conduits and spaces under sinks are useful places to check. Ghost silverfish seek quiet, sheltered locations, so inspections need to reach beyond the most visible parts of a room.

Sticky traps placed along wall edges are a standard, inexpensive monitoring tool. Staff should label and date traps and check them weekly. Recording the number of insects and each trap's location helps identify areas of concentrated activity and changes over time.

Active searches can reveal live insects running away from light, droppings that resemble pepper and delicate skins left behind after molts. Paper may look lighter where feeding has scraped away surface fibers. A flashlight should be ready when dusty skirting boards are disturbed, because silverfish often flee along edges.

Monitoring should include storage areas, reading rooms and loading docks. Traps at the junction between a floor and a wall can help detect arrivals near deliveries as well as insects already living among stored materials. Repeated checks are more useful than a single inspection of a room that appears tidy.

Stopping arrivals at the collection door

Every incoming loan, donation and purchase should be inspected in a separate intake area. Quarantine means keeping newly arrived materials apart from the main collection while staff check them for pests. Incoming boxes should be held in a controlled space, and outer cardboard should be inspected and bagged before it reaches the stacks.

Outer packaging should be removed and discarded outside collection spaces. When the materials of an object allow it, staff can hold it in a sealed bag or bin with a sticky trap for observation. Rarely used papers, maps and photographs can be stored in sealed plastic containers or archival boxes.

Lending partners should be asked for a recent update on pest activity. Outgoing items should have clean inner wrapping, while outer cartons remain separate from collection areas. After deliveries arrive, staff should promptly break down and remove external cardboard.

A few traps in loading areas can catch insects before they spread farther into a building. These measures belong to a coordinated program that prevents entry, detects arrivals quickly and removes small populations before they grow. Many museums already use a similar approach against clothes moths and carpet beetles.

Cleaning, cooler storage and careful treatment

Cleaning needs to reach the places where food dust and insects accumulate. Staff should vacuum along baseboards, beneath shelves, behind shelving and into floor cracks, then dispose of the vacuum contents outside the building. Removing paper dust and starch residues reduces food in areas that routine cleaning can overlook.

Leaks and condensation should be repaired promptly, and humidity peaks reduced. Gaps around baseboards and at the bottoms of doors should be sealed. Keeping temperatures lower where possible slows development; even a reduction of a few degrees can lengthen the time insects need to grow and help keep populations in check.

Vacuuming and sealing cracks are the starting point for control. Where chemical treatment is necessary, licensed professionals should use targeted applications in cracks and crevices, away from sensitive collections. Treatment needs to address the hidden areas where insects live while protecting the materials being preserved.

Freezing or controlled heat may be suitable for some infested items, but conservation staff should approve their use. Treatments should be tested and documented to protect objects. The choice depends on what the item can safely tolerate.

Staff and volunteers also need a clear reporting route. A single contact person for sightings, trap captures and suspicious damage can speed the response. Periodic inspections of quiet spaces should continue so hidden populations have less time to grow.

What households can do

Homes can host ghost silverfish as well as cultural institutions. People may notice them in bathrooms, kitchens, basements or near stored papers. The insects avoid light and move about at night, so pale insects running quickly near books or boxes warrant early attention.

Householders can seal gaps around baseboards, reduce clutter and keep documents in sealed bins. Regular vacuuming along room edges and beneath appliances removes material that insects may eat. A dehumidifier can help where the air stays damp.

A few sticky traps can show how much activity is present. Heavy use of insect sprays should be avoided because residues can spread indoors while missing the concealed spaces occupied by the insects. Where activity is high, a licensed pest control provider can confirm the species and tailor treatment. Residents should mention that they suspect ghost silverfish.

What research still needs to explain

Scientists have yet to confirm the ghost silverfish's natural outdoor habitat. Since its description in 1910, the species has been reported only from buildings. Genetic work suggests close relationships among populations separated by large distances, pointing toward a common source and frequent transport by people.

Large European surveys have recorded rising captures in museums and homes, while a link between those increases and widespread damage to objects has yet to be documented. The conditions inside each building matter: paper chemistry, types of glue and climate all influence the risk to a collection.

Continued monitoring and careful records in Japan will help researchers determine the extent of the threat. Documenting insect numbers alongside feeding damage can give institutions a more detailed picture of what is happening in their own rooms and stores.

Japanese research has already described development and seasonal timing in local strains. Those findings support concentrating inspections in early summer, when egg laying peaks, and using cooler storage areas to slow growth. Future research will examine food preferences and the exact mechanism of parthenogenesis, which could help guide control.

The institute's planned information website is intended to standardize reporting and provide guidance. Its free traps and bait for facilities with confirmed infestations are another part of the response, alongside the daily work of checking deliveries, inspecting collections and recording activity.

The Bottom Line

• Ghost silverfish were first confirmed in Japan in 2022 and had reached 19 prefectures by late September 2025.
• Detections extend from Hokkaido to Kyushu, with documents, packaging and collection items considered likely transport routes.
• Females reproduce without males, allowing a single transported egg to start a population.
• Paper fibers, book bindings, starch pastes and some adhesives provide food, putting books and archives at risk.
• Incoming materials should be quarantined and inspected, with sticky traps used for regular monitoring.
• Cleaning hidden spaces, reducing humidity peaks and keeping storage cooler can support control.
• Homes can also host the insects; early monitoring and careful treatment can help address activity.
• The Tokyo National Research Institute for Cultural Properties plans an information website and offers free support materials to facilities with confirmed infestations.
• Research continues into the insect's outdoor habitat, feeding preferences, reproduction and the extent of damage to collections.