Order Zygentoma
Zygentoma
is an order of resilient, wingless insects frequently referred to as firebrats
or silverfish. A distinctive attribute about these isopod-like organisms is their
three long caudal filaments (Penn State). Silverfish earned their common name because of
their fish-like movement and typically gray color. The silverfish were formally
part of an order called Thysanura for upwards of a century until entomologists
recently discovered that it was a paraphyletic clade (Schulz). Zygentomae are relatively
close to the distant ancestor of the first hexapods, and as they aren’t part of
the superclass Pterygota, they are wingless. Silverfish aren’t part of
superorder Holometabola either, therefore they undergo incomplete
metamorphosis.
Silverfish resemble ancient trilobites because of their elongated and segmented bodies. Because this order of insects is so primitive, it is postulated that they may have conquered land as long as 140 million years ago. In fact, Zygentomae look very similar to Rhyniognatha hirsti, a specimen considered the world’s oldest known insect (Rhyniognatha). R. hirsti may have emerged on land about 400 million years ago, about the same time as Earth’s terrestrial ecosystems were first being formed. Silverfish are commonly mistaken for bristletails, as both orders have similar anatomical features. A distinguishable difference in the two clades is their movement: Silverfish generally squirm around while bristletails are capable of jumping.
Zygentomae occur throughout much of North America and Australia and are more commonplace in temperate climates. Silverfish can often be found in kitchens and bathrooms, as they generally prefer damper and darker environments. Since silverfish are primarily nocturnal insects, they typically hide under leaf litter and decaying bark during sunlit hours. A consequence of silverfish’ dark habitat is that some have minimal eyesight or some lack compound eyes altogether (Order Zygentoma - Silverfish). The insects likely rely on other sensory organs, such as their limbs for touch, to travel around and survive.
Aside from slight differences in size, the nymphs of Zygentomae heavily resemble adults. Adults can reach up to 15 millimeters in length, excluding their antennae and cerci (Order Zygentoma - Silverfish). Silverfish can molt throughout their life, which can occasionally last as long as six years. Unlike most insects, though, silverfish live most their lives as adults (this was demonstrated in the photo above illustrating the lifecycle of a silverfish). Reproduction in silverfish is almost always sexual and sperm is indirectly transferred. The males deposit a sperm packet called a spermatophore on the substrate, which is then picked up by the female and transferred to her spermatheca (Schulz). The spermatophore, once extricated of sperm, is ejected by the female and ingested as a source of food (Schulz). Silverfish’ reproductive rates are very slow, but this weakness is compensated for their longevity.
Zygentomae can survive several weeks without water, and up to a whole year without food! Silverfish are mostly phytophagous but can also feed on dead arthropods when the opportunity arises (PennState). Because paper and glue is a common byproduct of household products, these insects often opportunistically migrate inside houses for sustenance. Aside from nutrition, silverfish might move into homes because of the comparatively low risk of predation and darker environment. It is unclear whether or not silverfish experience territorialism with other conspecifics, but most entomologists have assumed that the insects live a rather solitary and lonely lifestyle.
Silverfish do not bite because their mandibles are so minute, nor do they carry any diseases infectious to humans. Silverfish can indirectly affect homes because they serve as prey to larger arthropods like centipedes and spiders. Additionally, silverfish have a bad reputation for harming household paraphernalia because they enjoy feeding on glue and wood-based products (Silverfish Facts and Treatment). Wallpapers can be torn off, books can be torn up, and furniture can be torn apart all because of the laborious work of silverfish.
While silverfish are quite disturbing in appearance and are infamously regarded as household pests, they do deserve recognition for their ancient appearance and high life span. Aside from aesthetic appearance silverfish are part of Earth’s intricate food web, thus they contribute to biodiversity. Larger predators probably don’t rely on silverfish for food, but the insects certainly contribute to availability and variety. Sometimes birds might want to take a break from the typical herbaceous snack and indulge on a segmented, eyeless, nocturnal insect instead.
 |
| Silverfish undergo incomplete metamorphosis, as illustrated above. Image Link: https://silverfishcontrol.blogspot.com/2015/12/what-you-need-to-know-about-silverfish.html |
Silverfish resemble ancient trilobites because of their elongated and segmented bodies. Because this order of insects is so primitive, it is postulated that they may have conquered land as long as 140 million years ago. In fact, Zygentomae look very similar to Rhyniognatha hirsti, a specimen considered the world’s oldest known insect (Rhyniognatha). R. hirsti may have emerged on land about 400 million years ago, about the same time as Earth’s terrestrial ecosystems were first being formed. Silverfish are commonly mistaken for bristletails, as both orders have similar anatomical features. A distinguishable difference in the two clades is their movement: Silverfish generally squirm around while bristletails are capable of jumping.
Zygentomae occur throughout much of North America and Australia and are more commonplace in temperate climates. Silverfish can often be found in kitchens and bathrooms, as they generally prefer damper and darker environments. Since silverfish are primarily nocturnal insects, they typically hide under leaf litter and decaying bark during sunlit hours. A consequence of silverfish’ dark habitat is that some have minimal eyesight or some lack compound eyes altogether (Order Zygentoma - Silverfish). The insects likely rely on other sensory organs, such as their limbs for touch, to travel around and survive.
Aside from slight differences in size, the nymphs of Zygentomae heavily resemble adults. Adults can reach up to 15 millimeters in length, excluding their antennae and cerci (Order Zygentoma - Silverfish). Silverfish can molt throughout their life, which can occasionally last as long as six years. Unlike most insects, though, silverfish live most their lives as adults (this was demonstrated in the photo above illustrating the lifecycle of a silverfish). Reproduction in silverfish is almost always sexual and sperm is indirectly transferred. The males deposit a sperm packet called a spermatophore on the substrate, which is then picked up by the female and transferred to her spermatheca (Schulz). The spermatophore, once extricated of sperm, is ejected by the female and ingested as a source of food (Schulz). Silverfish’ reproductive rates are very slow, but this weakness is compensated for their longevity.
Zygentomae can survive several weeks without water, and up to a whole year without food! Silverfish are mostly phytophagous but can also feed on dead arthropods when the opportunity arises (PennState). Because paper and glue is a common byproduct of household products, these insects often opportunistically migrate inside houses for sustenance. Aside from nutrition, silverfish might move into homes because of the comparatively low risk of predation and darker environment. It is unclear whether or not silverfish experience territorialism with other conspecifics, but most entomologists have assumed that the insects live a rather solitary and lonely lifestyle.
Silverfish do not bite because their mandibles are so minute, nor do they carry any diseases infectious to humans. Silverfish can indirectly affect homes because they serve as prey to larger arthropods like centipedes and spiders. Additionally, silverfish have a bad reputation for harming household paraphernalia because they enjoy feeding on glue and wood-based products (Silverfish Facts and Treatment). Wallpapers can be torn off, books can be torn up, and furniture can be torn apart all because of the laborious work of silverfish.
While silverfish are quite disturbing in appearance and are infamously regarded as household pests, they do deserve recognition for their ancient appearance and high life span. Aside from aesthetic appearance silverfish are part of Earth’s intricate food web, thus they contribute to biodiversity. Larger predators probably don’t rely on silverfish for food, but the insects certainly contribute to availability and variety. Sometimes birds might want to take a break from the typical herbaceous snack and indulge on a segmented, eyeless, nocturnal insect instead.
 |
| Damage done to baseboard in a house, probably by a silverfish. Photo found on https://getridpests.com/silverfish/get-rid-silverfish-bugs-look-like.html |
Works
Cited
“Bristletails (Silverfish and Firebrats) (Department of
Entomology).” Department of Entomology
(Penn State University),
ento.psu.edu/extension/factsheets/bristletails-silverfish-and-firebrats.
Egdb12. “How to Get Rid of Silverfish Bugs, and What Do They
Look Like?” GetRidPests, 3 June
2016,
getridpests.com/silverfish/get-rid-silverfish-bugs-look-like.html#prettyPhoto.
“Order Zygentoma - Silverfish.” BugGuide,
bugguide.net/node/view/79.
“Rhyniognatha.” Wikipedia,
Wikimedia Foundation, 30 Apr. 2018, en.wikipedia.org/wiki/Rhyniognatha.
Schulz, Katja. “Silverfish and Firebrats - Zygentoma - Details.” Encyclopedia of Life, eol.org/pages/1097/details.
“Silverfish.” Wikipedia,
Wikimedia Foundation, 18 May 2018, en.wikipedia.org/wiki/Silverfish.
Silverfish Control. “What You Need To Know About Silverfish
Bugs.” Silverfish Bugs,
silverfishcontrol.blogspot.com/2015/12/what-you-need-to-know-about-silverfish.html.
“Silverfish Facts and Treatment.” Fantastic
Pest Control, www.fantasticpestcontrol.co.uk/pest-profiles/silverfish/.
Wigglesworth, Vincent Brian. “Insect.” Encyclopædia
Britannica, Encyclopædia Britannica, Inc., 25 Apr. 2017,
www.britannica.com/animal/insect/Annotated-classification#ref303946.
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