Screamers are lizard liked aliens who work for the Myriad. They have two pairs of flaps that reasemble mosquito wings. It appears they are blind since its eyes are not visible, they have worm liked mouths that have lots of theeth in them and four fangs at the corners of their mouth. They acctually reasemble a bit of the Gigginox in the series "Monster Hunter". It attacks by screaming at enemies (as the name suggests) and do medium damage to them, this can prove that they have an extremely powerful scream sac in their bodies. Screamers can turn into spore throwers upon death (but you have to research "Spore Maggots" first).
Revenge after death- a tactic where many lower knots are produced, and are producing screemers in waves, to protect the growing sporethrowers left by other screemers. this tactic is very effectient because although screemers cannot attack airunits, sporethrowers can. they are less expensive than sporethowers.
It is possible that Screamers are sporethrower larva explaining why they turn into Sporethrowers when they die.