The fallen trees gave them all the best place that they could go to to rest. Without even waiting, they began to prepare the area. Jerold had learned to set a few basic traps. The easiest way to have some form of alerts to what was happening around them.
While they were basic trip wires or bell traps, this was a jungle. The wind was not strong enough to set them off unless it was a beast that was able to make enough wind to cause the bells to go off. Therefore, the trap was an excellent warning. However, Clark knew that these meager traps were not enough.
The spiders had a very fine way of traveling. They were used to using delicate movements and silently moving through the forest when they were hunting or waiting for prey. Therefore, it was very easy to imagine that they would be able to sneak up. But there were more beats to worry about.
Creation is hard, cheer me up!