Mark Zuckerberg must be smiling right now.

Instagram passed Twitter in daily active users on mobile in August for the first time, according to new comScore data provided to Mashable. Instagram had 7.3 million daily mobile users for the month, while Twitter had 6.9 million.

In fact, comScore's data shows that Instagram's daily active user count has almost increased tenfold in the six-month period starting in March, when it had 886,000 daily active visitors. Twitter's mobile user numbers have increased as well, but at a much slower rate. Part of this may simply be due to the fact that Instagram is a younger company, but it's impressive nonetheless.

Twitter did end up having more total unique visitors in August than Instagram overall (29 million vs. 21 million, respectively), but fewer of them returned on a daily basis, and Twitter's visitors spent less time on average viewing content than visitors to Instagram. Each of Instagram's mobile users spent an average of 257 minutes on the app (or more than four hours), while Twitter's users spent an average of 169.9 minutes from mobile (or a little less than three hours.)

The data comes from comScore's Mobile Metrix 2.0 tool, which uses survey data and on-device metering to provide a more comprehensive estimate of mobile usage for various websites and apps. The data factors in visits to the apps and websites for Instagram and Twitter from iOS, Android and BlackBerry mobile devices. However, it obviously doesn't take into account the number of active users who visit a website from a non-mobile device, which would certainly tilt in favor of Twitter.

Facebook acquired Instagram for around $735 million earlier this year (the deal was initially worth more than $1 billion, but the value declined with Facebook's stock.) In an S-1 filing earlier this year, Zuckerberg explained that part of the reason he wanted Instagram was to "enable users to increase their levels of mobile engagement and photo sharing."

The latest comScore numbers clearly show that Instagram has figured out mobile engagement. Now the question is: When will Facebook capitalize on this by finding ways to monetize Instagram? Twitter may have fallen behind Instagram in daily active users, but the social network already has an advertising model in place that is expected to help it earn more in mobile ad revenue this year than Facebook.

[Via AllThingsD]

Image courtesy of Flickr, The_Next_Step