“What is this worm?” asks this reader in his submission regarding the little, brownish worm pictured below. “Found among algae in the backyard koi pond in northern Illinois. Travels by attaching (perhaps by suction) one end and feeling around with the other. Can stretch to well over 4 times its resting length. Seeks air if submerged. Appears to be slightly flat. Was discovered clinging to hand. Found today. No discernible segmentation.” The thing that caught our eye in the excellent photo our reader sent in is the flattish part at one end of its body, which we assume to be its head. This is likely the part that it uses to “attach” itself to things and move along using, as our reader stated, “suction”. Based on this, as well as its appearance, we are inclined to say that this is likely a leech.