they were clearly aliens, and came from some extraterrestrial organism obviously, no big deal to me, some planet that had extraterrestrials and preds let an alien egg somewhere there
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for aliens to colonize planets theyr entirely dependant in something carriyng them, otherwise theid stick to their planet and destroy all, and wait till small surviving organisms evolved enough so aliens cud again destroy all and the cycle continues
in their planet there possibly existed some natural enemys!
small creatures like vermin (cud make a good snack) or worms, or simply damn huge guys that were no good for hosts (but cud be used for food if aliens were in big enough numbers.....) wud certainly survive alien infestation and evolve in some million years so aliens cud prosper again, (there would survive eggs only tough....)
aliens werent intended to space travel
thats my two cents