An insect from the planet Shaggai.

The Insects from Shaggai, or Shan, are a race of pigeon-sized, interstellar refugees who arrived on Earth centuries ago. The Shan hail from the planet Shaggai, a world that orbits twin emerald suns. In its heyday, the technologically advanced Shan lived in globular dwellings in huge cities. As devout worshippers of the Outer God Azathoth, they erected pyramidal temples containing "multidimensional gates" whereby "that from Outside" (an aspect of Azathoth called Xada-Hgla) could enter.

One day, a mysterious object appeared in the sky. Day by day, this object drew closer to Shaggai, until the third day when the strange celestial visitor emitted a red glow that destroyed the planet. Only those Shan in their teleporting temples of Azathoth survived the catastrophe. The survivors teleported to their colony on the planet Xiclotl, where their brethren had enslaved the native inhabitants.

The Shan remained on Xiclotl for some time, but upon discovering the frightening nature of their slaves' singular religious practice, they teleported to the planet Thuggon. A horrific find on this world prompted the Shan to flee once more, this time to the planet L'gy'hx, aka Uranus. When this world proved unsuitable, a small band of the Shan teleported to Earth, in a curious cone-shaped temple, arriving in the Severn Valley region of England sometime in the Middle Ages.

Most Shan have an aversion to sunlight because the electromagnetic frequency of the Sun's rays poisons their metabolism. As a result of contact with Azathoth, the head of the mythos pantheon, the Shan developed the ability of Kirlian Phasing, allowing them to pass into the skulls and brains of organic life. On Earth, they usually meld with their new favorite hosts, humanity. Once ensconced within the cranium of a human victim, they use cruel alien telepathy to gradually dominate and control their puppet. 

Their destruction was later carried out by the Outer God, Ghroth.