Damn Mexicans. But to answer the OP, no. As God created all life on earth only six thousand years ago obviously no extra-terrestrials have come to earth.
Why do you ask, Mammalian Sub-Creature?
:D:D:D:D
What makes you think accelerating to 25% of the speed of light is “very doable” ? Everything we know says it is extremely unlikely.
I’ve met many people who struck me as sub-human but not necessarily ETs. If ETs did come here and if we DID meet them, how would we identify them?
But this is pure speculation. If they used their magic wormhole generator, or rode frozen hyperspace, or used matter teleporters or just flew their dragons that can instantaneously move from one place to another by simply visualizing it then they could equally be here. But we have no evidence of any of that stuff…it’s just Sci-Fi and fantasy.
As for your idea here, first off getting something large enough to put people (or presumably space aliens) on up to 25% of the speed of light is beyond even our ability to conceive of it. It would take massive amounts of energy. Secondly, unless the ship instantaneously goes to 25% of the speed of light and has the ability to also stop from 25% of the speed of light instantaneously (which means they have some method to keep the crew alive through massive changes in inertia…1000’s of gravities that would otherwise turn the crew to paste) it’s going to take time to get the ship up to 25% of the speed of light (and keep the crew from becoming paste) and then time to spin it down from 25% the speed of light so that you could actually orbit the Earth or where ever you were trying to go. Then you have the problem of simply stocking enough provisions for such a long journey (hundreds of years at least). Plus, while space is vast and MOSTLY empty, it’s not completely empty, and when you are moving at relativistic speeds hitting even a small object would be…very bad. Hitting something bigger is going to be even worse, and if you are moving that fast it’s going to be difficult to dodge without, again, turning the crew to paste. Plus there is all that radiation stuff out there you have to worry about.
Oh, and about a thousand other things. None of which we, as a species currently know how to do…or even have a good theoretical model that could be worked up to engineer the solutions to such problems. What we have right now is Sci-Fi writers who can envision stories that incorporate those things into their stories. Now, I’m as big a Sci-Fi fan as anyone, but it’s fiction…not reality. So…bottom line is that ETs coming to Earth is an extraordinary claim that requires extraordinary proof, or it shouldn’t be taken seriously.
-XT
The difference between belief in God, angels and et cetera and the belief in alien life visiting earth is most religious people will openly and honestly admit that their belief is based on faith. A few extremists will try to say they can scientifically “prove the existence of God” but that’s a relatively rare position to take. Sans proof, you’re talking about faith. That’s fine if you’re witnessing, but if not then your claims are subject to the same burden of proof as anything else. Under that rigorous framework there is just no credible evidence that aliens have visited Earth, period.
This elicits a “wtf” reaction from me.
Do you understand where you’re posting these comments?
The number of active participants here who believe in the things you mentioned… I wouldn’t be surprised if it was less than 10.
Now I am sad. I’ve seen many aliens but no bobcats.
Well, we could start here…
I have to go feed my Venus Fly-Trap 
Sorry but that just tickled me for some reason.
Yeah, no kidding. This is clearly a poster who hasn’t taken the time to look around and get the feel of the place.
They do require good green blooded alien steak to keep them in fine health. 
No worries. That’s what I get for posting from my iPad.
-XT
I admit that I’m taking the above quote slightly out of context, but to answer this part of your question, I think it is easy for some people to believe in such things because of the way they were raised. For example, I am a product of a Christian home and anything I might have said as a little boy that supported a Christian worldview would have stood a good chance of being validated by some member of my church or family. This leads me to the following:
For the record, I am not trying to belittle you, your family, or your ideas. Rather, I’m just trying to give you food for thought. I hope this is taken in the friendly manner that I intend it.
(edited because of typos)
Oh, we’d identify them alright. Given the creature evolution that would have had to independently occur without the slightest help from Earth, don’t you think that their appearance would be so different from us (BEMs, large green, slimy lizard things, whatever)? If you postulate they have a way of knowing human language and changing their shape to blend in, well, you are piling much fantasy upon fantasy.
I’d like to thank the OP for visiting earth and wish him a safe ride home.
I’ve seen an ET. It had 3 of them…
Oh, you meant “Terrestrial”. I thought you meant “Testicle”.
The funny bit for me is that Carnivorous plants like the Venus Fly-Trap are mentioned in very persistent legends as coming from outer space because of their peculiar chemistry and native locations close to meteorite impact sites.
Alas, that idea did not came from serious researchers, but likely from the woo-woo 70’s book "Strange Creatures From Time and Space”. by John A. Keel.
Here’s the thing. Any species capable of traveling across interstellar distances must necessarily be far more technologically advanced than us, right? And they either want us to know about them, or they don’t. Well, whichever they want, they have the technology to easily accomplish it. If they wanted us to know about them, they could introduce themselves in such a way that would leave no possible doubt for anyone on the planet, and if they wanted to hide, they could hide so effectively that we’d never notice any trace at all of them. Any phenomenon you care to name that you would argue is evidence of aliens among us must, then, be something else, because true alien visitors (if they exist) would never be so clumsy.
Depending on how you define “extraterrestrials,” I suppose it’s within the realm of physical possibility that some kind of anaerobic microbial life forms, or maybe fungus or something that is capable of surviving indefinitely in outer space could make it’s way to earth on a meteorite. It would also have to be able to survive burning up when it hits the atmosphere, I guess, but I think, while such a possibility is extremely remote, it’s non-zero.
The kind of thing the OP is talking about, though - virtually no chance. I also don’t think you can solve the distance problem by saying the “come here metaphysically.” That is semantically no different than saying, “they travel by magic.”
This makes assumptions about their motivation. Isn’t it also possible that they don’t much care about the future of this little blue planet one way or the other, but are instead indulging in some recreation, perhaps an advanced version of Town vs Scum, with the teams competing to recruit humanoids just for their own amusement?
Hmmm. Come to think of it, this seems not unlikely. I can think of a few politicians who may be Scum recruits (if not actual ET’s themselves).