A female Trachelipus rathkii with one of her offspring in Allegany Co., Maryland (6/12/2024). The offspring, known as a manca, had just exited the mother's marsupium, a temporal brood pouch located between the front five pairs of legs.
A Trachelipus rathkii molting in Frederick Co., Maryland (5/13/2024). Isopods undergo biphasic molts in which one half of the exoskeleton is shed first. After the newly exposed exoskeleton hardens, the second half is then shed. This allows the isopod to maintain mobility during the entire molt period, thus reducing their vulnerability to drowning during periods of heavy rainfall.
Key characteristics helpful for the identification are (1) the presence of two uropods, the pointed appendages that extend off the back of the posterior end; (2) the outside edge of the final main trunk segments is even with the outside edge of the first pleon segment; (3) the segments are covered with fine bumps; and (4) the presence of five, not two, pleopodal lungs on the vent.
A Trachelipus rathkii (underside) in Howard Co., Maryland (4/26/2014). Determined by Eric C. Maxwell/BugGuide.
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Ashley Bradford.
A Trachelipus rathkii in Allegany Co., Maryland (4/8/2017). Determined by Scott Loarie/BugGuide.
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Media by
Bill Hubick.
A female Trachelipus rathkii with one of her offspring in Allegany Co., Maryland (6/12/2024). The offspring, known as a manca, had just exited the mother's marsupium, a temporal brood pouch located between the front five pairs of legs.
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Media by
Dave Webb.
A Trachelipus rathkii molting in Frederick Co., Maryland (5/13/2024). Isopods undergo biphasic molts in which one half of the exoskeleton is shed first. After the newly exposed exoskeleton hardens, the second half is then shed. This allows the isopod to maintain mobility during the entire molt period, thus reducing their vulnerability to drowning during periods of heavy rainfall.
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Media by
Dave Webb.
Ventral view of Trachelipus rathkii in Calvert Co., Maryland (1/19/2022). Verified by Nathan Jones/iNaturalist.
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Dave Webb.
Trachelipus rathkii in Prince George's Co., Maryland (10/16/2012). (c) Sam Droege, some rights reserved (CC BY).
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Media by
Sam Droege.
Trachelipus rathkii, also known as Rathke's Woodlouse, is a species of woodlouse in the genus Trachelipus (family Trachelipodidae). It can be found across Europe, except in the Mediterranean Basin.[1] It has also been introduced to North America, where it can be found across most of the northern half of the United States and southern Canada.[2] They have been recorded as far west as Alberta.[3]
Rathke's woodlice grow to 1.5 centimetres (0.59 in) long.[4]