A Shrieker is a Hive class that possesses a metallic body containing an energy core inside. It lies dormant until provoked or if the player is within close proximity of it, at which point it will split into multiple pieces that float around its core.
"Void-infused sentinels, Shriekers serve as immobile but animated sentries of the Hive's dark holds." 
Shriekers directly spawn, or phase into existence during a battle, giving them the element of surprise, so be alert of their presence during major Strike battles, as they are often located in easily-defensible terrain. 
From a safe distance and position, Shriekers are generally easy to eliminate due to their lack of mobility. Remember to keep your eyes out for one, because the biggest strength of the Shriekers attack is one of surprise.  When a Shrieker appears, find nearby cover. If you are too close, make your way to a more distant position, and then take it out.
Once a Shrieker is destroyed it will launch void bolts, similar to the axion bolt of Voidwalkers, that will follow players until they hit or explode prematurely. Another reason to keep away from a Shrieker is that they explode with Void energy upon death, inflicting damage in a small radius.