The Mist

After a violent thunderstorm, David Drayton (Thomas Jane) leaves his wife Stephanie (Kelly Collins Lintz), and with their neighbor Brent Norton (Andre Braugher) goes into town to buy supplies for repairs. David brings his eight-year-old son Billy (Nathan Gamble) and Norton to a grocery store, where the patrons notice unusual police and military activity. Moments after a panicked and injured man, Dan (Jeffrey DeMunn), runs in warning of danger, a thick mist envelopes the store, accompanied by earthquake-like tremors and the town's tornado siren. A man disregards the warnings and is attacked while running to his car.
A mentally unstable religious woman, Mrs. Carmody (Marcia Gay Harden), decides that this is the beginning of Armageddon. A shaken woman (Melissa McBride), against objections from the others, leaves the store to go home to her children and disappears. While investigating the store's generator, a bag-boy named Norm (Chris Owen) volunteers to go outside, but is snatched and pulled into the mist by a tentacle connected to an unseen monster.
Norton heads outside with a small group to seek help, only to be attacked and killed, prompting the rest of the survivors to barricade the shop-front windows. That night, enormous insects land on the windows and pterodactyl-like animals attack them, breaking the glass and allowing the creatures to begin fighting inside the store. One of the insects lands on Mrs. Carmody, but doesn't sting her because she keeps still during her prayer. As a result, she starts preaching more and quickly gains followers among the distraught survivors.
A trip to the neighboring pharmacy to gather medical supplies goes horribly wrong and two people are killed by giant spiders. Mrs. Carmody's faction now contains most of the survivors. Two soldiers commit suicide, and a third, Private Jessup (Samuel Witwer), reveals that the local military base was filled with rumors about the Arrowhead Project, the government's attempt to look into other dimensions, and that the scientists responsible for the experiment may have inadvertently opened a doorway into a dimension containing the creatures that are now invading the town. Mrs. Carmody convinces her followers to blame Jessup and he is stabbed and ejected from the store, quickly falling prey to a large praying mantis-like creature.
David and a handful of other survivors secretly gather supplies to flee, but are discovered by Mrs. Carmody. She attempts to have David and his group sacrificed, but Ollie (Toby Jones) shoots and kills her with Amanda Dumfries' (Laurie Holden) gun, horrifying her followers. Realizing all that they have done, they stand down and allow David's group to leave, but only David, Billy, Dan, Amanda, and Irene (Frances Sternhagen) make it to the car.
Driving through the mist, David finds his house destroyed and his wife dead. Devastated, he drives the group south, passing destroyed vehicles and seeing a gigantic six-legged, tentacled beast. When they run out of gas, the group decides there is no point in going on. David shoots the others rather than have them endure horrifying deaths, but is left with no bullet to use on himself. He leaves the car and waits to be killed, but the mist suddenly recedes, revealing that the U.S. Army has arrived, rescued whatever survivors, and restored order. Among the survivors is the woman who left the store at the phenomenon's onset, accompanied by her two children. David breaks down with the realization that they were only moments from being rescued and had likely been driving away from help the entire time.

Question: what are  breaking the glass and and fighting inside the store?
Answer: Enormous insects; Enormous insects