As far as youkai go, Wriggle is quite young, only about 70 years old (though to any member of the insect kingdom, this is positively ancient), and so her power as a youkai is rather weak. Wriggle was alive during the flower incident of 1945, but at that time was still just another firefly, so at this point she hardly remembers that incident, much less comprehends the importance of it.
During the events of Imperishable Night, Wriggle sensed that there was something off about the moon that night. For whatever reason, the strange moon made the insects in the Forest of Magic go crazy. Wriggle was attempting to calm them down and make sure they didn't cause trouble in the human village. Wriggle could sense that there were humans traveling through the forest even this late at night and originally began following them to make sure that the insects didn't cause them trouble, but when she got closer, she could sense that there were youkai traveling with them. Wriggle saw this as very suspicious and attacked them, presuming that they might have some knowledge of why the moon was like this, but was handily defeated.Wriggle decided not to get involved in the more recent flower incident on the basis that getting involved really wouldn't do any good. With this many flowers blooming, the insects would have much more nectar to eat this spring. No sense in looking a gift horse in the mouth, right? A week or so after that however, she was suddenly beset upon by a certain crow looking for her next prey (so to speak). She eventually drove Aya away, but not before she managed to get a few embarrassing photos of her.
Currently, she lives in the Forest of Magic and is most often seen near Marisa's house. Marisa can sometimes be rather careless when disposing of failed magical experiments and Wriggle needs to make sure that they don't adversely affect the insects or plants (since Marisa would certainly blast her into next week if Wriggle actually tried confronting her about it...).
Despite what some fans might think, Wriggle is not really associated with Cirno at all and, in fact, can hardly stand her presence. Only part of it has to do with Cirno's childish personality though. Wriggle's main problem with the fairy is that it's always cold when she is nearby.
Wriggle has a naturally aggressive and combative personality balanced out with a strong sense of responsibility and a hint of shyness. Left to her own devices, she is a quiet and unassuming individual, though she doesn't take insults well and is quick to pick a fight. True to her insect nature, Wriggle is easily surprised, but because of her antennae, it's very difficult to actually sneak up on her, so she is more likely to be spooked by sudden, unexpected movement. She quickly gets defensive whenever her subjects are concerned. Concerning humans though, Wriggle realizes that she should set an example for her subjects to follow and at least attempts to be polite to humans (at least the ones that don't purposefully kill her subjects), but sometimes her mouth gets ahead of her, especially if she's in a sour mood. In spite of her impulsive personality, Wriggle is actually rather intelligent and is one of the few youkai that can read.
ZUN states that Wriggle's special power is the ability to manipulate insects. However, in his usual vague fashion, it's never really explained how this ability works. Most tend to assume it's simply magic, but I wanted to take it in a bit of a different direction. The true answer is not magic, but biology.
While Wriggle looks human enough, If a skilled surgeon were to cut Wriggle's throat open, he would find a small gland just above her larynx that isn't present in humans. This gland creates pheromones that are released into the air whenever Wriggle exhales. Other insects can smell these pheromones and, depending on what they smell like, they can be interpreted as a message. Wriggle, while she isn't aware exactly how it works, has more or less conscious control over what messages these pheromones transmit, and it is through these messages she is able to "command" large numbers of insects in quite a wide radius.