Other mistake: The wood coffin that Jerry Manley is placed in has no bottom. Right after showing him in the coffin they seal the top, insert handles and somehow carry him off.
Revealing mistake: At the end when the dock 'kicks' the king spider off him into the fire, we hear it scream like a stuck pig. Then additional screams from the 'burning' spiders inside the pulsating nest, and when the doc torches both the king spider afterwards.
Suggested correction: Not sure how this is a mistake. Sure real world spiders don't making squealing noises but real world spiders also don't jump 30 feet or have venom potent enough to kill a human within seconds of being bitten.
It's a mistake because spiders cannot vocalize at all. The film creates a new spider species with exaggerated aspects of real life spiders: extremely potent venom, highly aggressive behavior, jumping ability, etc. What the film can't do is give the spiders traits they couldn't possibly have in real life.
Factual error: The shadow of a spider climbing up the window makes a 'tick'ing sound as it moves, when spiders don't make sounds.
Revealing mistake: When the General is lowering himself towards Jennings on a string of web, there's a couple of shots where the spider is completely immobile, revealing the spider to be a prop. Most noticeable just before Jennings smacks him with a wine bottle.
Revealing mistake: When Atherton is using his fog machine to spray up into the tree look to his left, you can see another spray of the fog being added to the tree by an unseen stagehand.
Visible crew/equipment: Near the end when the doctor and his family are getting attacked by the spider's, half are CGI and the others fake as you can see the Tech wires making them move. Then when he's lying on the floor collecting himself, there's a pulsating sack in the corner, with a fake spider leg sticking out.
Visible crew/equipment: When the explorer goes up into the loft to find the king spider, he taps the fake web string, says 'suppers ready" and then the fake spider dramatically shoots out from a tech wire 'screaming", and attacks him. (01:49:24 - 01:49:50)
Revealing mistake: When Margaret (the blood pressure lady?) gets settled for the night, one of the baby spiders is crawling toward the couch where she's sitting. In the very next shot that same spider is suddenly 'hiding' inside the lampshade above her and bites her.
Visible crew/equipment: Near the beginning when the men are hauling the equipment to their camp, you can see a crew members hand in the bush literally toss the fake giant spider on top of the passing equipment. (00:13:10)
Continuity mistake: After Becky's dad comes into the bathroom, and she screams, covering herself with the shower curtain, you can see her brother, who had died at the football game considerably earlier in the movie, through the bathroom's doorway, standing in the hall. It's only for a split-second, but as long as you're looking in the right spot, it's very clear.
Other mistake: When Dr Atherton injects the mouse with venom, the syringe is pointing up. But as the plunger is pulled nearly all the way back and the syringe is too large to be filled with venom, he would have injected the mouse with air. (01:17:00)
Revealing mistake: Near the end it is way obvious that the king spider is animatronic as it goes for the doctor, considering it's tech string is quite visible in the closeup. And it "hisses" as it's lowered.
Other mistake: When the exterminator steps on the little spider it makes a loud dramatic 'crunch' and then when he lifts his boot the bottom is overcovered in fake brown goo.
Revealing mistake: Two very different types of spiders are used in most of the shots. In the closeups they are larger, with bulbous legs, defined hairs, and big eyes.
Continuity mistake: It's way obvious that the king spider attacking the doc at the end is animatronic as its appearance changes. In the far shots the legs are wide spread and it's a purplish color. But in the closeups it's black and half the size.
Other mistake: Near the end when the doctor is pursuing the fake king spider moving along inside the pipes, it makes loud, exaggerated tapping sounds, and then "jumps" out at him from the end pipe and attacks.
