Continuity mistake: In the scene where the spiders are starting to attack the city, it shows the guy in the barber shop closing up. He shuts the blinds then his friend gets attacked by the spiders, then he goes back out in front and the blinds are still open.
Continuity mistake: Something weird happens as the sheriff rolls under the closing gate. She's holding a shotgun before she drops to the floor, rolls under with empty hands (seen from both sides), and as she stands up she's got it back. What's weird is that her dropping and rolling is one continuous shot, so she must have deliberately thrown the gun offscreen as she fell to help her fit through the narrow gap. She doesn't throw it through the gap - we'd be able to see it on the other side.