Pica pica = itchy itchy
Pica pica are the larval form of the thimble jellyfish. And jellyfish have "nematocysts," a microscopic stinging device triggered by touch. Sea lice, the larval form of the jellyfish, can also sting, especially if trapped between a bathing suit and the skin.
As Marty pointed out, Pica Pica has a season. You may recall that I told you that if asked, I would have said that mid-April was the best time to dive Belize. However, that is Pica Pica season. I was lucky and never encountered any on my trip. A friend of mine was in Coz at that same time. We met up in Belize at the end of my vacation. My friend was absolutely covered in welts. Looked terrible, felt worse.