ARTHROPOD MUSEUM NOTES

Number 37 • October 6, 2005 • Jeffrey K. Barnes

Silverfish
Order: Thysanura
Family: Lepismatidae
Genus and species: Lepisma saccharina Linnaeus

Silverfish, Lepisma saccharina


Insects of the Order Thysanura are known as bristletails. They are ancient and primitive. Living species are relatively small omnivores. They run rapidly and hide to escape predators, but the extinct Ramsdelepidion schusteri reached the size of jumbo shrimp as it wandered the prehistoric coal swamps of the Upper Carboniferous. It was well equipped with sensory bristles, which assisted it in responding to air currents produced by predators. It had leg-like mouthparts with claws and a complete set of abdominal leglets. Bristletails are primitively wingless, they display little or no metamorphosis, and they continue to grow and molt after reaching sexual maturity. Juveniles resemble adults in body form, microhabitat, and food requirements. Several abdominal segments bear delicate style-like appendages, and the elongate tail-like appendages consist of a median caudal appendage and paired cerci. Thysanurans display complex courtship behavior. The sexes do not engage in copulation, and sperm transfer takes place externally and indirectly.

Three families occur in North America, but only one, the Lepismatidae, is found in Arkansas. Of the 14 species of Lepismatidae recorded from the United States, only four are native to the country. Of the four species known or likely to occur in Arkansas, only one is native to the state (Allacrotelsa spinulata Packard). The others have been introduced by, and live in association with, man. They are rarely, if ever, found in wild populations. Ctenolepisma longicaudata Escherich, has not been recorded from Arkansas, but it is known from the neighboring states of Missouri and Louisiana. Lepisma saccharina Linnaeus, the silverfish, and Thermobia domestica (Packard), the firebrat, are rather common and widely distributed species of economic importance.

The silverfish is a common household pest in many parts of the world. It is scaly, has a silvery sheen, and it is about half an inch long at maturity. It is active at night and hides during the day. It prefers cool, damp situations, developing and reproducing best at 72-81°F and 75-97% relative humidity. Individuals frequently attain an age of well over 3 years and under favorable conditions may lay an average of about 100 eggs. Immature and adult stages consume items containing carbohydrates and protein. Silverfish are primary pests of paper and paper products containing starch, dextrin, casein, gum, and glue. They are cannibalistic, feeding on cast skins and dead and injured individuals of their own species. They will also attack leather, furs, carpets, and starched fabrics.

The firebrat, a cosmopolitan household pest, is tan or brown and about the same size as the silverfish. It is a general scavenger, consuming and damaging items that contain carbohydrates and protein, including starchy paper and cloth, wallpaper, and cereals. It probably originated in a tropical climate. Its optimal environment is a warm 99°F with 84% relative humidity. This species frequents warm places associated with heating facilities. Its common name is a reflection of the fact that this species used to be found around outdoor ovens in England.