Silverfish

Silverfish are small, wingless insects in the order Zygentoma (formerly Thysanura). There are four families: Lepidotrichidae (single species), Lepismatidae (about 200 species), Maindroniidae (three species), and Nicoletiidae (about twenty species). In the late twentieth century, it was recognized that the two suborders were not sister taxa; therefore Thysanura was paraphyletic, and the two suborders were each elevated to the status of an independent monophyletic order, with Archaeognatha the sister taxon to the Dicondylia, including the Zygentoma (fishmoths, firebrats, and silverfish). A nicoletiid, Speleonycta ozarkensis, occurs in eight different cave systems in Arkansas in Benton and Newton counties and in Oklahoma in Adair, Cherokee, and Delaware counties.

In concert with jumping bristletails (Order Microcoryphia), the predecessors of silverfish are considered the earliest, most primitive insects. They evolved in the late mid-Devonian Period and possibly as early as the late Silurian Period more than 400 million years ago. Some fossilized arthropod trackways from the Paleozoic Era, known as Stiaria intermedia and often attributed to jumping bristletails, may have actually been produced by silverfish. The extinct Lepidotrix is known from specimens preserved in Baltic amber.

The silverfish are composed of cosmopolitan species, specifically in Africa, the Americas, Australia, Eurasia, and parts of the Pacific. They inhabit moist areas, requiring a relative humidity between seventy-five and ninety-five percent. In urban areas, they can be found in attics, basements, kitchens, old books, and showers. Silverfish can sometimes be found in bathtubs or sinks, because they have difficulty moving on smooth surfaces and can become trapped.

Silverfish are moderately sized or small nocturnal insects that avoid light and are typically 13 to 25 mm (0.5 to 1.0 in.) long. They have three long caudal filaments, the lateral ones being the left and right cerci, while the one between is a medial cerciform appendage, specifically an epiproct or appendix dorsalis. Their mouthparts are mandibulate, have long antennae, and are wingless with two small compound eyes (or absent). Ocelli may be present or absent, and their bodies are covered with fine scales. Their eleven-segmented abdomen tapers at the end, giving them a fish-like appearance.

Silverfish typically live for two to eight years. They are swift runners and can usually outmaneuver most of their predators. However, escape is possible only on horizontal surfaces, as they lack any additional appendages and therefore are not quick enough to climb walls at the same speed. Earwigs, house centipedes, and spiders are known to be predators of silverfish.

Reproductive rituals may last over half an hour and involve three or four phases: (1) the male and female position themselves face to face with their quivering antennae touching, then repeatedly draw back and return to this position; (2) the male then runs away, and the female chases him; (3) the male and female stand abreast and head to tail, with the male vibrating his tail against the female; and (4) the male lays a spermatophore (a sperm capsule covered in gossamer), which the female takes via her ovipositor into her body to fertilize her eggs. The female deposits groups of about sixty eggs at once in small crevices. These whitish eggs are ovoidal-shaped, about 0.8 mm (0.031 in.) long, and hatch in two weeks to two months.

When the nymphs hatch, they look like smaller adults and are whitish in color. As they molt, the young develop a grayish appearance with a metallic shine, eventually becoming adults after three months to three years. They may go through anywhere from seventeen to sixty-six molts in their lifetimes, sometimes thirty in a single year. Interestingly, silverfish are among the few types of insect that continue to molt after reaching adulthood.

Silverfish consume lignocellulose found in wood and starchy polysaccharides, such as dextrin found in adhesives. These may include book bindings, carpet, clothing, coffee, dandruff, glue, hair, some paints, paper, photos, plaster, and sugar. They are capable of damaging wallpaper in order to consume the paste and also cause destruction to tapestries. Other substances they may eat include cotton, dead insects, linen, silk, or even their own exuvia (molted exoskeleton). When typical food items are scarce, a silverfish may even attack leatherware and synthetic fabrics. If only water is available, silverfish can live for a year or more without eating.

Due to their consumption and destruction of property, silverfish are considered household pests. However, although they are responsible for the contamination of food and other types of damage, they do not transmit diseases.

The family Lepidotrichidae contains a single species, Tricholepidion gertschi, which occurs in northern California under decaying bark of fallen Douglas fir trees (Pseudotsuga menziesii). This species is an example of a living fossil, as it is the only remaining member of a clade that was once widespread.

The family Lepismatidae is distributed nearly worldwide in warm regions and includes Lepisma saccharina and the firebrat, Thermobia domestica. Both are anthrophilic species that live in buildings. Three other common silverfishes in this family in North America include the gray silverfish, Ctenolepisma longicaudata; C. quadriseriata; and the urban silverfish, C. urbana. The Australian species most commonly referred to as silverfish is a different lepismatid, Acrotelsella devriesiana.

The Maindroniidae is a very small family containing a single genus, Maindronia, and three species. These distinctive silverfish are strictly coastal, being found along the arid coastline among seaweed in Chile and Peru.

The family Nicoletiidae are small, pale species that live in soil litter, in humus, under stones, in caves, or as inquilines in ant or termite colonies. In Benton and Newton counties in Arkansas and in Adair, Cherokee, and Delaware counties in Oklahoma, a nicoletiid, Speleonycta ozarkensis, occurs in eight different cave systems. It is the only troglobitic nicoletiid from the Ozark Highlands. Although there are no current species formally considered to be at conservation risk, several are cave-adapted troglobites limited to one or a few caves or cave systems, and these taxa are at a high risk of extinction.

For additional information:
Adam, J. A. “Biological Notes upon the Firebrat, Thermobia domestica Packard.” Journal of the New York Entomological Society 41 (1933): 557–562.

Arnett, Ross H., Jr., and Richard L. Jacques Jr. Simon & Shuster’s Guide to Insects. New York: Simon & Shuster, 1981.

Blanke, A., M. Koch, B. Wipfler, F. Wilde, and B. Misof. “Head Morphology of Tricholepidion gertschi Indicates Monophyletic Zygentoma.” Frontiers in Zoology 11 (2014): 11–16.

Borrer, Donald J., and Richard E. White. A Field Guide to the Insects of America North of Mexico. Boston: Houghton Mifflin Company, 1970.

Engel, M. S. “A Note on the Relic Silverfish Tricholepidion gertschi (Zygentoma).” Transactions of the Kansas Academy of Science 109 (2006): 236‒238.

Espinasa, Luis, E. Collins, and M. Botelho. “Two New Nicoletiid Species (Insecta: Zygentoma) from the Yucatan Peninsula, Mexico.” Proceedings of the Biological Society of Washington 127 (2014): 473‒482.

Espinasa, Luis, N. D. Bartolo, D. M. Centone, C. S. Haruta, and James R. Reddell. “Revision of genus Texoreddellia Wygodzinsky, 1973 (Hexapoda, Zygentoma, Nicoletiidae), a Prominent Element of the Cave-Adapted Fauna of Texas.” Zootaxa 4126 (2016): 221‒239.

Espinasa, Luis, N. D. Bartolo, and S. A. Sloat. “A New Epigean Species of the Genus Anelpistina (Insecta: Zygentoma: Nicoletiidae) from Sierra de El Abra, Taninul, Mexico.” European Journal of Taxonomy 156 (2015): 1‒7.

Espinasa, Luis, M. Espinasa, Danté B. Fenolio, Michael E. Slay, and Matthew Niemiller. “Distribution and Conservation Status of Speleonycta ozarkensis (Insecta: Zygentoma: Nicoletiidae) from Caves of the Ozark Highlands of Arkansas and Oklahoma, USA.” Subterranean Biology 14 (2014): 51‒62.

Espinasa, L., C. Flick, and G. Giribet. “Phylogeny of the American Silverfish Cubacubaninae (Hexapoda: Zygentoma: Nicoletiidae): A Combined Approach Using Morphology and Five Molecular Loci.” Cladistics 23 (2007): 22‒40.

Espinasa, Luis, Stephen Furst, Thomas Allen, and Michael E. Slay. “A New Genus of the Subfamily Cubacubaninae (Insecta: Zygentoma: Nicoletiidae) from Caves in South-Central and Southwestern USA.” Journal of Cave and Karst Studies 27 (2010): 161‒168.

Espinasa Luis, K. Parker, and S. A. Sloat. “Identification of a New Population of Anelpistina inappendicata (Insecta: Zygentoma: Nicoletiidae).” Speleobiology Notes 8 (2016): 10‒15.

Espinasa, Luis, and K. Socci.  “A New Species of Anelpistina (Nicoletiidae: Zygentoma: Insecta) from the Selva Lacandona Rainforest in Mexico.” Proceedings of the Biological Society of Washington 127 (2014): 466‒472.

Fenolio, Danté. Life in the Dark: Illuminating Biodiversity in the Shadowy Haunts of Planet Earth. Baltimore, MD: Johns Hopkins University Press, 2016.

Grimaldi, David, and Michael S. Engel. Evolution of the Insects. Cambridge: Cambridge University Press, 2005.

Jian-Zhong, Sun, and Michael Scharf. “Exploring and Integrating Cellulolytic Systems of Insects to Advance Biofuel Technology.” Insect Science 17 (2010): 163–165.

Mendes, L. F. “New Species and New Data on Protrinemuridae and Nicoletiidae (Zygentoma) from Eastern Asia and Pacific Islands.” Annales de la Société Entomologique de France 38 (2002): 399–433.

Smith, G. B. “Review of the Australian Nicoletiinae (Zygentoma: Nicoletiidae).” Invertebrate Taxonomy 12 (1998): 135–189.

Tahami, M. S., R. Molero, M. Gaju, and S. Sadeghi. “Discovery of Representatives of the Family Nicoletiidae (Insecta: Zygentoma) from Caves of Iran, with Descriptions of Two New Supraspecific Taxa.” Zootaxa 4369 (2018): 253–269.

Torgerson, R., and R. D. Akre. “Reproductive Morphology and Behavior of a Thysanuran, Trichatelura manni, Associated with Army Ants.” Annals of the Entomological Society of America 62 (1969): 1367–1374.

Triplehorn, Charles R., and Norman F. Johnson. Borrer and DeLong’s Introduction to the Study of Insects. 7^th ed. Belmont, CA: Thompson Brooks/Cole, 2005.

Wygodzinsky, P. “Description of a New Genus of cave Thysanura from Texas (Nicoletiidae, Thysanura, Insecta).” American Museum Novitates 2518 (1973): 1–8.

———. “A Review of the Silverfish (Lepismatidae, Thysanura) of the United States and the Caribbean Area.” American Museum Novitates 2481 (1972): 1‒26.

Chris T. McAllister
Eastern Oklahoma State College

Henry W. Robison
Sherwood, Arkansas