Lice

Before the plague of ערב,  Moshe warns Pharaoh וְשַׂמְתִּי פְדֻת בֵּין עַמִּי וּבֵין עַמֶּךָ לְמָחָר יִהְיֶה הָאֹת הַזֶּה. As mentioned on this blog last year there is a debate in the Rishonim was this separation between between Klal Yisroel and the Egyptians only introduced in the fourth plague or existed by the first three plagues as well.  The Ramban explains all the plagues didn't affect Klal Yisroel but only regarding the wild beasts which naturally would spread throughout the entire land, the Torah needs to emphasize that they didn't enter the land of Klal Yisroel.
The Mishna in Avos (5:4) says עשרה נסים נעשו לאבותינו במצרים.  The Rambam explains the miracles are that Klal Yisroel was saved from the plagues.  He shows that for every plague it is at least מדיוק in in the possuk that it wasn't affecting Klal Yisroel except for the plague of כינים.  For that we must rely upon the tradition of Chazal that it didn't affect Klal Yisroel that it didn't harm Klal Yisroel however, he says the lice were among Klal Yisroel.  In his words: לשון התורה בכל מכה ומכה מהם שהביא הקב"ה על המצריים מלבד מכת הכנים שלא באר זה אלא שהוא ידוע שלא ענש ישראל אבל היו נמצאים אצלם ולא היו מצערים אותם וכן בארו החכמים.  This would argue with the Ramban that says all of the first three plagues didn't enter the land of the Jews.  However, the opinion of Rambam needs an explanation; why would the lice be found where Klal Yisroel lived if they weren't affected by any of the plagues?
We see that there are two aspects to the plagues of the lice.  One aspect was if one's body becomes attacked by lice it hurts.  However, there was another aspect as well.  Many of the Rishonim explain that the lice covered the entire country of Egypt.  There wasn't an inch of land that was lice free.  According to one interpretation of the Chizkuni, that's why the sorcerers couldn't reproduce the plague.  In order to tap into their magic powers they had to be attached to the ground and they couldn't because there was lice crawling over every inch of turf.  דבר אחר: ולא יכלו – לפי שכל עפר הארץ היה כנים ולא היו רגליהם נוגעות לארץ וכל זמן שרגליו של מכשף אין נוגעות אין כשופו מצליח.  This aspect of the plague wasn't meant as a punishment to the Egyptians, rather to Egypt.  They were being separated from the land itself to demonstrate that they aren't even in control of where their feet are standing.  This message of detachment from the land was meant for Klal Yisroel as well.  You aren't attached to the land under your feet, this isn't Jerusalem, its Berlin , I mean Goshen and you don't belong here.  You will be taken out of this land and brought to where you belong.  Don't feel settled here.

Another explanation from the אזנים לתורה: