A Shrieker showing its thermal flaps.
Shriekers are the bipedal-second stage of the Graboid, a worm-like reptilian creature with similar features. Unlike a Graboid, Shriekers have flaps of tissue that detect thermal signatures of their prey- they are deaf.
Physiology
Shriekers are much smaller than the Graboids, about 5 feet long and 4 feet tall, though despite this they have great strength. Shriekers are very agile and can run up to 25 mph or faster (speculation), on three-toed feet and stubby legs. The Shriekers have distinctive patches of red on their necks and tails, as well as the inside of their mouths. Born in 'litters' of three, Shriekers are very social, living in huge herds of hundreds if possible. Parent Graboids die while giving birth due to the fact that the Shriekers seem to eat their way out of the Graboid.
They have flaps for infrared detection on their heads, though these do not have to be fully open to function. It was said in a Stampede Entertainment FAQ that this is similar to opening eyes wide. This also enables communication, which they achieve by letting out heat in screams. Certain parts of their body also seem to have a greater concentration of blood vessels, so perhaps these also allow communication or identification (as they never seem to attack each other).
Shriekers have long prehensile tongues that they use to manipulate objects such as door handles. The tongue is about three feet long, and covered in bristles. It is capable of distinguishing between foodstuffs and other materials, indicating an ability to taste.
Like all other stages of the Graboid's lifecycle, Shriekers have thick orange-red blood.
Intelligence
Shriekers have been shown to create novel ways to beat problems, such as climbing over each other to reach prey out of their normal grasp. However, they seem to be generally governed by an instinctual desire to attack hot things.
Reproduction
When shriekers consume sufficient food, for example MREs, people or chickens, they reproduce asexually and the new, smaller shrieker is dropped from the mouth. This new shrieker is cocooned in membrane, and is quickly able to grow and move.
Development
The Shriekers molt and develop into the Ass-blaster, a lankier version that combusts chemicals produced in its rear to fly through the air.