WARNING: There are SPOILERS ahead for WandaVision episode 7.
When Wanda is alone in Agatha's house for the first time in episode 7 of WandaVision, she pays close attention to a cicada crawling on the curtains. At first, the bug just seems to add to the eerie atmosphere in her neighbor's home, but upon closer examination, it may very well be a reflection of the plan set in motion by the show's villain.
During "Breaking the Fourth Wall," Agnes graciously takes Wanda's kids off her hands for the day. But when Wanda goes to Agnes' home to fetch Billy and Tommy, it's clear that something isn't right. As she sits in the living room by herself, Wanda looks around and takes in everything that seems amiss. Chief among those is a cicada clinging to Agnes' curtains. The camera lingers on the bug, suggesting to the audience to pay attention.
The cicada in WandaVision represents something deeper than a dirty home. The WandaVision episode ends with Agnes revealing that she is none other than ancient sorceress Agatha Harkness. This reveal is clearly a part of Agatha's master villainous plan, and the cicada in her home is a reflection of that.
Cicadas tend to represent a state of renewal, rebirth, and transformation. That's because the bugs undergo a huge level of transformation in their own lives. Cicadas spend their entire development period burrowed underground. That timespan will last anywhere from 2 to 17 years. Once that period is over, they emerge above ground, where the cicadas spend the remainder of their lives. When they come above ground, the cicadas need to transform themselves in order to adapt to their new surroundings.
The cicada's lifecycle can be viewed as a direct reflection of Agatha and her ultimate plan for Wanda. For the majority of WandaVision season 1, the villainous Agatha was hiding in plain sight. Like the young cicada, Agatha was waiting for the right time to emerge. Once that time revealed itself to her, Agatha transformed herself into the powerful sorceress that she is. But the WandaVision antagonist appears to be taking the theme of rebirth to the next level. Agatha has proved that she is powerful enough to pull the strings in Westview. The seemingly magical items hidden in her lair show that Agatha has everything she needs to shape the world in her own image. That will likely come back into play by the season 1 finale of WandaVision.