Rock Bristletail - Family Meinertellidae
Order Microcoryphia
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Live adult bristletails photographed in the wild at northern Illinois, USA. Size: 15mm (body only)
Rock Bristletail dorsal view
There are about 22 species of bristletail in 12 genera in 2 families in North America, with 350 species worldwide [1].  Bristletails prefer outdoor, grassy or wooded environments; under tree bark, in leaf litter and rock crevices, under rocks. These specimens were found living in an outcrop of Ordovician dolomite and sandstone at Lowden State Park near the Rock River in Oregon, Illinois. Often confused with silverfish, bristletails are not normally found inside homes and do not reproduce indoors.

It is thought the bristletail lineage is ancient. Earliest fossil evidence of such creatures appear in Devonian rocks about 390 million years old. The Ordovician sedimentary rocks this specimen lives in are about 450 million years old, deposited in near-shore or marine environments. At this time, Illinois lay in the tropics south of the equator; a warm, shallow sea alternately flooded and receded for millions of years [3].

Bristletails can take as long as 2 years to reach sexual maturity, undergoing eight or more molts. Genders exist separately but do not copulate; the male leaves a parcel of his sperm on the ground for the female to pick up (how thoughtful) each time she wishes to fertilize a batch of eggs (she cannot store sperm like a queen bee does.) Some species have courtship rituals in which the male spoils the Easter-egg-hunt quality of the operation by pointing out to his prospective mate where he left the spermatophore.

Rock Bristletail lateral view
Bristletails are insects with six legs; in addition, abdominal segments 2-9 each bear a pair of a styli (singular: style) - short, stiff appendages moveable by muscles (above). These may be vestigial remnants of ancestral limbs [2]. Specialized abdominal musculature gives bristletails the ability to jump away from danger by snapping the abdomen and the whip-like medial filament against the substrate.
Rock Bristletail dorsal view
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References
  1. Bugguide.net, "Order Microcoryphia - Bristletails"
  2. Tree of Life, "Archaeognatha - Bristletails"
  3. Special thanks to Mary J. Seid, Illinois State Geological Survey for her help with identification and her
    excellent bedrock maps of the Oregon and Mt. Morris quadrangles in Illinois.
Helpful: You can hear the pronunciation of many scientific and taxonomic terms at howjsay.com
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