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)
Other mistake: Irv and Blaire's death scene doesn't make sense. When Irv poured butter on the popcorn, he should've noticed the spider in the bowl. Also, when Blaire picked the spider up, she should've felt it. Both of them still appeared to be watching the TV after being bitten, which also didn't make sense. Why didn't they have seizures like the other victims?
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.
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.
Other mistake: The king spider moving up the docs leg at the end is animatronic, considering the way it moves, like a typical Halloween effect. But understandably because it was too risky to use a real one.
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.
Answer: The small spiders are Avondale spiders from New Zealand. They are totally harmless to humans.
Hamster ★