Passage Summary: Guam is crawling with spiders compared to other islands, and scientists think it's because snakes ate all the birds that used to eat the spiders.

Conclusion: The massive increase in Guam's spider population was caused by the decline of native bird species.

Reasoning: Brown tree snakes eliminated most native birds, and birds are natural predators of spiders and consumers of their webs.

Analysis: We need to bolster the causal link between the bird disappearance and the spider explosion. Look for an answer that rules out other causes or shows that islands with birds don't have this spider problem. It would be particularly helpful to confirm that the spider boom happened chronologically after the birds vanished, rather than before the snakes arrived.