Human are mostly bind and naive to consider things including our environment that we wrongly assumed that the environment can be really designed and decided by us and planed by us and we indeed ignored a whole lot of reality.
Bacteria Virus Micro Organisms Insects etc shares the same environment with us, we neglected and ignored them most of the time. We don't really have the kind of control which we wished we had, to determine what gets into our living space and what does not. And then we come to this sort of question about how things got there without our design and approval.

The bacteria and bugs and lizards are there at the location's environment ever since before human arrived on this red dot. Weather the building was a new construction or redevelopment it is still done within the same environment. They are there during the entire construction phase and they will be there even after the building became so old and abandoned or pulled down. If you had been to construction sites you would see them. Ants lizards cockroaches bugs mosquitoes etc. They are not including within the building material list nor drawn in the blue prints but they are there. They did not received your house warming invitation cards, but they are there, and they are there before all the human occupants.

:p
Planet earth is wrongly perceived by human that we are in full control or permanently occupy. It existed for hundreds of billions of years before human and will still be here way after human existence. We are temporary form of live here in planet's lifespan, and planets' lifespan will also be over, as we know that is happening in universe.
Human would be more humble and honest if we really knew how minute and temporary we are within the universe & time. Our silly civilization had very wrongly impressed and misled ourselves about our own existence and made us so foolish and self-centered and myopic and greedy.
http://www.ibtimes.com/articles/213401/20110914/x-ray-attack-space-planet-attack.htm
Planet Under Ferocious X-Ray Attack by its Star
By IBTimes Staff Reporter | September 14, 2011 2:44 AM EDT
Our planet is not under attack by aliens, but astronomers have found a star that is bombarding its planet with a barrage of X-rays that are almost 100,000 times stronger than what Earth receives from the sun.
(Photo: )<br>Photo: NASAStar lashes out on close- by planet
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(Photo: )
Photo: NASAStar lashes out on close- by planet
For now the planet, dubbed CoRoT-2b, has a mass about three times Jupiter's, but data gathered by NASA's Chandra X-ray Observatory and the European Southern Observatory's Very Large Telescope suggest that its survival is in doubt as it is losing about 5 million tons of material every second due to the high-energy radiation.
The study was published in the journal Astronomy and Astrophysics.
"This planet is being absolutely fried by its star," said Sebastian Schroeter, an ESO astronomer of the University of Hamburg in Germany. "What may be even stranger is that this planet may be affecting the behavior of the star that is blasting it."
With an extremely active star orbiting the planet in very close proximity, CoRoT-2 is one of the most unusual planetary systems yet discovered.
The star, dubbed CoRot-2a, is located about 880 light-years from Earth and its estimated age is between 100 million and 300 million years,, which makes it fully formed and mature. Although old, the star is still very active and is capable of producing very high X-ray emission levels like younger stellar bodies.
Destruction of the planet may be useful, as some scientists pointed out that the size of CoRoT-2b is "too big." It is believed to be a form of self-correction, by some researchers, that will eventually die down with time, io9.com reported.
"We're not exactly sure of all the effects this type of heavy X-ray storm would have on a planet, but it could be responsible for the bloating we see in CoRoT-2b," said Schroeter. "We are just beginning to learn about what happens to exoplanets in these extreme environments."