Entomology (Study of Bugs)/Silverfish


QUESTION: I just moved into an apartment that had been empty 3 months. Daily, when pulling the built-in cutting board out, I saw a silverfish rush back toward the dark. I found a small one in the sink. I sprayed Orange Guard and found another small (dying) one in the sink, and another in a bowl several cabinets over. Pesticide company put out boric acid bait. I learned that a neighbor in the building (5 units) has silverfish and has seen 2 in the last month. Why would an unoccupied unit (mine) have many more silverfish than an occupied one (neighbor's), the latter presumably having more food for silverfish? Will they likely be more numerous in my apartment once the boric acid is gone, now that I'm living in it (and am not fastidious)? Does my neighbor seeing 2 in one month indicate high numbers of silverfish in the building? I'm used to seeing one every few years, that's my 'normal'. I'm considering moving if the building has a high population. Are there clues about the population in any of this? Thank you for your help!

ANSWER: Dear Barbara - You really don't have to worry about the occurrence of a few silverfish; they pose absolutely no health threat to humans, and they very seldom are numerous enough to cause any real damage to items such as wallpaper or book bindings. See http://tinyurl.com/yoj6bl for a publication that gives very detailed information on the biology of and control methods for these insects. One thing to bear in mind is that they require high humidity levels to thrive in an indoor environment, so lowering indoor humidity levels as much as practical would be a good first step in keeping them at bay.

Hope this helps,

---------- FOLLOW-UP ----------

QUESTION: Dear Saugy,
Thank you for your reply.  When are their numbers considered an infestation? Is there any way to determine if the entire building is infested?  The number I saw scared me because I've never seen that many.  I don't like the idea of them crawling on kitchen counters and dishes while I sleep.  I've never been fastidious and have never found one in my kitchen sink. Also I leave cat kibble out at night. So, you think the boric acid bait will result in fewer of them in the long term?
Thanks, Barbara

Dear Barbara - Again, although I can appreciate that you object to their presence from an aesthetic standpoint, I can assure you that the silverfish present absolutely no health threat to you or anyone in your household (see http://tinyurl.com/mvozksv). That aside, I believe that a combination of the boric acid treatment and lower indoor humidity should keep them at bay. Just as an aside, we live in the country and often have various and sundry insect 'visitors', so we keep all non-refrigerated foodstuffs in sealable plastic (Tupperware) or glass containers, and don't worry about it. The only insects that I really would be concerned about finding in our house would be termites.

Entomology (Study of Bugs)

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Ed Saugstad


Will accept most questions in general entomology, including those related to medical entomology, taxonomy, ecology, arthropod surveillance, and pest management. If you are requesting a 'mystery bug' identification, PLEASE either attach an image to your question, or post an image on a web page (such as Flickr) so that I can look at it, as verbal descriptions frequently are insufficient for a definitive identification.


21 years in the U.S. Army as a medical entomologist; duties varied from surveillance of pest populations (including mosquitoes, cockroaches, ticks, and stored products pests) to conducting research on mosquito-virus ecological relationships and mosquito faunal studies. Ten years as a civilian analyst for the Department of Defense, primarily on distribution of vector-borne diseases worldwide. Limited experience on surveillance of agricultural insects in North Dakota and Indiana.

Entomological Society of America, West Virginia Entomological Society, Society for Vector Ecology, National Speleological Society, West Virginia Association for Cave Studies.

American Journal of Public Health, Contributions of the American Entomological Institute, Japanese Journal of Sanitary Zoology, Journal of Economic Entomology, Mosquito News, and Mosquito Systematics.

B.S. in entomology from North Dakota State University in 1963, M.S. in entomology from Purdue University in 1967.

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