One of the main (human-originated) species in Blame!.
Silicon creatures are cybernetic organisms at war with the humans. One of their main traits is their emotions and temper, capables of feeling fury and curiosity. They have their own identities and personalities (even then, many are downright psychotic killing machines). Each one has its own distinctive look, but all of them are anthropomorphic, looking as females or males and often seen banded in male-female pairs.
Their Japanese name in the original manga is 珪素生物 (keiso seibutsu), which is actually a general science fiction term for Silicon-Based Life Forms.