I wrote about the yellow morphs of the common terrestrial isopod Armadillidium nasatum from my backyard. Last weekend, also in my backyard, I found a yellow Porcellio scaber, another relatively common isopod.
The usual color of this species is gray. According to Hopkin (A Key to the Woodlice of Britain and Ireland, 1991), orange and cream morphs may be found, "especially near the sea". But I don't live near the sea.
What's behind the recent appearance of these yellow morphs in the backyard? Perhaps color morphs are periodically produced during the natural cycle these animals, although I have no idea what function they may serve.
Post revised 18 April 2008: In the original post I had identified this isopod as Porcellio spinicornis. Thankfully, both Joan Jass in Milwaukee and Ferenc Vilisics in Budapest e-mailed me to point out that the animal was actually P. scaber.