San Antonio Express-News reporter Paul Stephen said he was shopping at the North Side San Antonio H-E-B when he picked up the decoration outside the store. He saw the spider hanging onto one of the tree's branches.
"I saw the spider, snapped the requisite Instagram pic, put it down and moved on to the next tree," Stephen told mySA.com. "Black widows aren't that uncommon, so it didn't occur to me to freak out."
H-E-B spokesperson Dya Campos told the site that the trees are sent to stores within 48 hours of being chopped, so they can have "elements of nature" with them.
"It's wise to shake out insects while shaking out the needles before putting a tree in a house. Similar to, in Texas we are accustom to shake out our boots before putting them on," Campos said in a statement.
Black widow spiders are famous for the red hourglass mark on their abdomens. Their venom is toxic, but David Ragsdale of the Department of Entomology at Texas A&M University told mySA.com it is not usually lethal to humans.
"Although the venom in a black widow is fairly toxic, the spider has a difficult time piercing human skin and most people are large enough that the venom is not lethal," Ragsdale explained.
Lifehacker points out that they rarely bite, with one study finding that repeatedly poking them made them run away instead of bite.