Reddit reviews Keeping the Praying Mantis: Mantodean Captive Biology, Reproduction, and Husbandry

You might also want to ask r/mantids , but a quick amazon search turned this up. Assuming your friend has an interest in raising them, it seems like a great choice. I've raised a few myself, and they're really a lot of fun and pretty easy to take care of. This store sells them, and r/invertpets can always answer his questions.

As for more general insect ecology, A Buzz in the Meadow is a great read. The Forest Unseen covers more than just insects, but is very engaging and well written.