Having grown up on a farm and learning from the time I could walk how to handle them, interact with them or best leave them alone (certain snakes) it never really bothered me to find a lizard or two running along the wall boards or trying to make a mad dash across the floor. They are perfectly harmless (unless eaten, so make sure cats and dogs are not involved).
In fact, lizards tend to show up in areas that have high insect activity. While this is likely the outside of your home, they sometimes find their way inside in their quest, out of confusion or because of extreme weather conditions such as heat, rain or even cold.
I open the door and tap a broom along behind them to guide them in the right direction.
If they'll fit underneath a paper cup, put the cup over them and slide a piece of cardboard gently underneath (cut a paper plate in half to get that edge that will slide under a cup). Carry them out and let them go. Remember, they are natural pest control!
They are pretty innocuous biters too - their displays makes it look worse than it will actually be (a pinch that even as kids we never minded), but be careful to scoop them rather than grab by the tail ! They DO drop their tails and this is probably the most disconcerting thing you'll witness. The tail wiggles and squirms for quite some time after coming off, which is a distraction and bait for the predator trying to eat the lizard. Meanwhile the lizard is off and running! Don't worry, they re-grow a new tail in a relatively short time, but until then they have nothing to leave behind if they encounter a new predator that may be serious about eating them!
Blocking vents with screens and other points of entry might help keep them out, but to be honest, I've had them inside and there's no way I can imagine them entering other than following me in through an open door without me noticing.
Finally, it is really important to show them the way out one way or another. If these lizards stay inside, they will die. Our homes are not the environment they need and will not supply the food and conditions required to support their life.
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