If you are going to be teaching a class or doing an art project and you need images of insects or spiders, check out Insects Unlocked. Their goal is to supply high quality public domain insect photographs for anyone who needs to use them.
Examples downloaded from their Flickr photostream:
How about an image that shows the diversity of beetles?
I also like how the credits are included with the image. Its always a good idea to make sure the source and/or photographer gets credit even with public domain images. This site makes it easy to do.
If you use one of their images in a project, feel free to leave us a comment telling us about it. We'd like some ideas about how they are being used.