Lord Of The Rings: 10 Things You Didn't Know About Orcs
4. Orcs Were Weakened By The Sun
Orcs were tortured creatures; apart from the odd bit of man-flesh, they really didn't have much to look forward to. Even the sun pissed them off.
It's to be expected, though; if you spend your whole life skulking around in caves, or living it up in the gloomy realm of Mordor, daylight is bound to give you headache.
But the orcs were so averse to the sun, it actually made them dizzy and sick. Tolkien made this clear as early as The Hobbit, stating: "They don't like the sun; it makes their legs wobble and their heads giddy".
One of the reasons Saruman interbred orcs and men, was to make them more resistant to daylight. This was mentioned briefly in the extended version of the Fellowship of the Ring, but Tolkien made many references to it in his writings.
During the Two Towers, Merry & Pippin are hostages of the Uruk-hai. The hobbits note that the Uruk-hai don't seem to mind the sun, whereas many of the northern orcs are hesitant to move in daylight. In the Return of the King, Sauron sends a darkness across the land, stretching out even to Rohan. This was to ensure his orcs were not effected by the sun while they made War on the people of Middle Earth.