Who is Darklings and Slithers from Midnighters #3: Blue Noon and what is their importance?

Darklings and slithers are ancient creatures that once dominated life in the desert. They come in a variety of shapes and sizes and can change their appearance at will. They typically take the form of their prey's nightmares. Their weaknesses include intelligence, the number 13, and multiples of 13 as well as language, or words with 13 letters. Technology, light and heat also inhibit their ability to function.