Terrestrial Isopods's Journal

Our resident woodlice hunter @cedric_lee strikes again. This time he found an observation of a rare woodlice that lives communally with ants called Platyarthrus aiasensis.

This species is from the Mediterranean and was first discovered in the Americas in 1989. It has since been reported from CA and TX with just 2 observations total in GBIF proving that this is a rare find indeed!

In May @berkshirenaturalist posted an observation another member of the genus Platyarthrus hoffmannseggii in CT. Its also non-native to the US but has become established in the North East. Its smoother and flatter than Platyarthrus aiasensis.

This brings our woodlice species count for the US up to 33. Still a small fraction of the 113 reported species from the US meaning there's still alot to discover - get out there and find me some woodlice!

Also apologies for the US focus to this post. Lots of cool woodlice postings coming in from elsewhere, but I definitely lack the expertise to put most of the non-US species in context (I also lack my secret weapon Prof Wright from Pamona @jcwright - who has been invaluable helping confirm IDs). If you are or would like to become/recruit a woodlice 'expert' in your neck of the woods, join our effort!

The Pacific Coast of North Amer from Alaska to Baja CA have 2 native species of Ligia or 'rock louse'. Based on GBIF records and this atlas, the native Ligia pallaisi is supposed to range from Alaska to the San Francisco bay (with a disjunct Santa Cruz population). The native Ligia occidentalis is supposed to range from the California border south to ~ the tip of Baja in Mexico.

The above pic compares the two with Ligia occidentalis at the top. Ligia pallaisi and Ligia occidentalis can be distinguished by the width between the eyes (wide in the former, narrow in the latter) and the length of the 'uropods' (forked tail parts) which are shorter in the former and longer in the latter.

There's also the introduced Ligia exotica from Southern California south into the tropics with even longer uropods which are greater than 1/2 the body length

Odd then to find these two (here by @nanorca13 and here by @chlorophilia) observations of whats pretty clearly Ligia occidentalis in Canada based on uropod length. Here's one of @chlorophilia's photos:

This site does mention Ligia occidentalis in BC, but as I mentioned above, GBIF records and the recent major treatment on these guys don't have any records of these north of CA. So this counts as a discovery in my book. Nice work gang, keep the observations coming!