The small energy beings are a race which inhabits the moon known as M4C-862. They are able to pass through matter such as trees, stone and other living beings, seemingly causing burns to whatever matter they pass through. They are harmless unless provoked, but they do have the capability to kill.
The entities of light are perfectly harmless and do not pass through mortal flesh unless one of two factors occurs:
- Cadet Jennifer Hailey's hypothesis: The moon's energy fields are in a state of magnetic flux while it passes over the magnetic pole of the gas giant it orbits, causing the light aliens to go into an angry frenzy.
- Major Samantha Carter's hypothesis: The beings are capable of communicating and relaying threats to one another. Not only does this mean they're intelligent, but they are also territorial and possibly sentient.
Either is likely, but the SG teams being attacked by the creatures were not going to wait around and find out. When penetrating the body, the light beings essentially "cook" the surface of the flesh, and possibly the inside of the body as well. Repeated attacks can be fatal.
The SG teams determined an erratic disturbance in an electromagnetic field, such as a human's, repels the creatures. Colonel Jack O'Neill volunteered to be zapped by a Zat'nik'tel in order to reach the Stargate and dial Earth.
For a matter of minutes O'Neill's bio-electric alteration repelled the creatures, but not long enough. It took a rescue by Teal'c with the zat to continue to fight off the creatures until the Stargate was active. Once done, the enormous superconductor created its own, greater field of electromagnetism, allowing the teams to escape. (SG1: "Prodigy")
A similar, if not identical race was encountered by the Atlantis expedition on Light Bugs' Planet. However, they seemed harmless and had a taste for military-issued energy bars. (SGA: "The Defiant One")