Noah Navarro Duarte was in his cousin's kitchen in Guará, São Paulo, earlier this month when he noticed the large arachnid scuttling on the floor.
He subsequently called his mum and sister over to see it, with the former recording the creepy-crawly.
But as Noah went to kill the creature with a flip flop, mum Lillyan captured the moment the spider's unborn babies were released across the tiles.
She gasped: "My God, she was pregnant!"
Providing some background to the viral video, Noah told Brazilian news site BHAZ: "It was a drizzly day and the house has a very big garden. It wasn't the first time a spider had turned up there.
"I was alone in the kitchen, saw the spider and realised it was very big. I was going to kill it straight away, but as it was a bit different, I called my mum and sister over to see.
"My mum came in already filming with her mobile phone. When I started to whack it with my flip flop, I realised why the spider was so big: it was expecting spiderlings."
Noah said he had thought about exterminating the animal with spider killer but was worried about it running away, so opted for the flip flop instead.
He was criticised for his course of action on social media though, with the spider identified as a harmless wolf spider; however, Noah insisted he had no choice.
He said: "I'm not in favour of killing, either; I know how important spiders are for the environment.
"It's just that my cousin lives with her young daughter and the spider had 200 spiderlings. I was scared of returning it to the garden only for the spiderlings to come back to her house.
"The scene might not have been pretty, but I think I did the right thing. It was necessary."
Hold on, I thought you said you didn't know it was pregnant until you whacked it? Get your story straight Noah, jeez.
Anyway, Noah would have been better off placing a glass or container over the spider, before slipping some paper underneath and releasing it somewhere suitably far from your house.
That way, no spider or spiderlings die, and no kitchen floor ends up with a thousand crushed legs on it.
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