In mid-April, Gemma McLean noticed that her Instagram account was getting some stealthy attention from her ex-boyfriend.

Instagram’s stories feature lets users see who has viewed their posts, and McLean saw that her ex had viewed her stories for four days in a row. So she decided to make sure he knew she could see his snooping.

McLean posted a screenshot to her Instagram story of the television show “Riverdale” with the message: “Hey PSA: if ur my ex I dumped in literal 2012 when I was still at high school: I can see u checking my insta story everyday lmfao.”

Such is the tangled web that Instagram users now weave thanks to a small feature that has developed an outsize impact on the social zeitgeist.

“My thought process was honestly just getting the message across to him that I can see him being a creep without having to actually talk to him in the hopes that he would stop,” McLean, 24, who lives in New Zealand, said. “Nothing like being lowkey publicly humiliated to put you in your place.”

There’s a riverdale screen cap for every occasion pic.twitter.com/SktTi1kenM — 𝓖𝓮𝓶𝓶𝓪 (@chiisaitamago) April 14, 2019

Instagram first introduced stories in 2016 and now more than 500 million users access it daily. Stories allow users to compile pictures, video and text snippets throughout the day, with those posts available for only 24 hours unless the users asks to save them.

But stories has a quirk rarely seen in social media. Users generally have to make a conscious decision to look at another person’s story by tapping on the small bubbles that appear at the top of the app, and the people who post stories can see which users opted to see their posts.

While that might sound like a small detail, it has given rise to a peculiar social dynamic, creating a cat-and-mouse game for users looking to catch exes, crushes, former friends and parents looking at their posts. Tales of teens and young adults wondering about why a certain person, like a new boyfriend’s ex-girlfriend, is watching their Instagram story are now commonplace on sites like Reddit and Twitter. Others have posted about their excitement when they catch their crush watching their stories.

But the stories feature has also been something of a reality check. For younger people who have grown up with social media, stories have provided a window into just how many people are actually seeing their posts.

McLean said Instagram’s stories feature has given her a private glimpse of who’s looking at what she posts on the platform — not just who decides to publicly comment or tap a heart.

“It is also handy to be able to see if unsavory folk are being nosy so you can take the best course of action,” McLean said, adding that the feature can help her identify people she needs to block.

Why we love to look

Stories first appeared on the messaging app Snapchat, but were soon copied by Instagram, Facebook and a variety of other social media platforms.

Instagram’s stories feature has outperformed its competitors, even surpassing Snapchat, according to CNBC. While other apps like Snapchat and Facebook allow users to see who has watched their stories, Instagram has dominated the feature.

Instagram declined to comment to NBC News for this story.

Stories are beloved and used religiously, and it has also caused people to adjust their behaviors on the app.

Instagram has already been criticized for its propensity to exacerbate some of human nature’s worst social media instincts, and the stories feature adds another layer to the issue. While the main Instagram feed can play into insecurities and warped beauty standards, the stories feature preys upon user’s desire to know their exact social status.

One reason we have a need to know who’s looking is the drive to know where we fit in in our social world, according to Pamela Rutledge, director of the Media Psychology Research Center.

“We care about who responds because we place different weighting on who responds,” Rutledge said. “By knowing who [the people looking] are and recognizing people, we enhance the emotional engagement factor.”

The other component is the dopamine hit people get when they get feedback from a social media post, Carrie Goldman, an author, educator and speaker, specializing in social media behaviors and bullying prevention, said.

“When teens are putting out their stories, the motivation is the dopamine hit they get and the reward in their brain when they see people are looking at it,” Goldman said. “It’s a direct dopamine hit and that’s true for adults, too.”

Experts say that the ability to see who is looking at your Instagram story gives teens and young adults some sense of where they fall in their social hierarchies.

But some users say for them, it’s just fun to know who is going out of their way to view their content.

McLean, who noticed her ex-boyfriend watching her stories, said she has no plans to outright block him from her page.

“It’s honestly mostly hilarious to me that he still thinks of me after all this time,” she said.

“Representing myself”

When Sophie Evans posted a picture of herself and her partner to her Instagram story in recent weeks, she was doing more than sharing an image with friends — she was hatching a small social experiment.

Evans, 24, who lives in Wales, was fishing for answers to a question about who was looking at her posts, and she noticed the ex-girlfriend of a colleague had been watching. That person didn’t follow Evans and had a private account, leaving Evans to deduce that the ex-girlfriend was manually searching for her account in order to watch her stories.

“I love the fact I can see who’s looking at me especially when I know they’re not following me on Instagram,” Evans said. “I sometimes post stories deliberately so I can actually see who is viewing me and if they follow me or not.”

Imani Gayden, 24, a social worker in Las Vegas, often switches the settings on her profile between public and private. She said she’s been on Instagram for the past seven years, but recently started using it more.

Gayden said she’s careful about what she posts on her story, knowing some of her family members can see her posts. Instagram recently introduced a feature that allows users to share their stories with only “close friends.”

“I want to share what I’m doing but make sure I’m representing myself well,” Gayden said.

Evans and Gayden said they have both checked out Instagram profiles that they didn’t follow, scoping out the content of a mutual friend or distant connection, but Gayden said she’s careful not to view the person’s story.

“I try not to watch their story because that lets you know I’ve been on their page,” Gayden said.

Evans, on the other hand, said she had viewed stories of people she didn’t follow.

“I know I can be bad for looking at other people’s Instagrams without following them because I like to be nosy too at times,” Evans said.

Evans said she’s completely unbothered knowing her colleague’s ex-girlfriend is looking at her posts. She said, if anything, it has become more of a game for her, attempting to see what that person will look at next.

“Now I’m aware she has been looking at my Instagram, it’s made me want to post more stories,” she said.