Quickly, now knowing what he was fighting, Simon looked down at the ground and the walls around him. Wand pointed, he shouted out, "Incendio!" Fire shot out of his wand in the direction of the spiders. He repeated this every time he found a new one crawling away from the fire.
When one got just a bit too close to him, Simon lifted a foot and stepped on it, smashing it beneath his shoes. When they were all on fire and finally smoldering down, Simon turned back to the two girls. "Can you stand?" He knew it was a stupid question as soon as he asked. If she could stand, she would have been doing so and killing the spiders on her own. "I can't lift both of you with my wand." That would have been a bit more concentration and skill then he had at the moment. He was already out of breath as it was.
Bending down, he checked out Hermione, two fingers at her neck to check that she was still breathing and her heart rate was somewhere near normal.