'Naked and Afraid' Contestant Finds Ticks on Penis

There's a big downside to sleeping naked in the jungle, and these "Naked and Afraid" contestants are experiencing it firsthand ... ticks absolutely love genitals!!!

The painful lesson unfolds on the upcoming episode of Discovery's "Naked And Afraid: Castaways" ... when one castaway wakes up to find a handful of ticks attached to his penis!!!

Ya gotta see the video, obtained by TMZ ... Andrew Shayde is just waking up when he discovers the unwanted visitors making camp on his dong ... and he counts them off, one at a time.

Andrew's clearly rattled ... he says he's super worried about his "little castaway" and is freaking out.

For Andrew, it's the latest painful encounter with ticks ... in a past challenge, the parasites got in his butt crack.

Sounds like fellow contestant Patrick French dodged a bullet ... he says ticks embedded between his legs, but they avoided the "prime real estate."