So, I've made a start. First up is Yahoo's image search, which I've wrapped as http://darwin.zoology.gla.ac.uk/cgi-bin/yahoo.cgi. You just append "q=" and the search terms to get a result. Try an example search for images of the ant Atta mexicana. Note that I currently just support the return format, not the query format (that'll come later). The query result is RSS 1.0 because it contains RDF (RSS 2.0 and Atom don't, and hence for my purposes are beside the point). The upshot is that I can now use this search in other projects, and making a better iSpecies becomes simply a case of adding a bunch of OpenSearch sources together.
Generating the RSS proved "fun", but the feed now validates as RDF, although Feed Validator grumbles slightly. It's all a bit of a black art, but I had to nest the RDF payload in <content:item> tags, like this:
<dc:description>Leaf-cutter ants (Atta mexicana ) ... </dc:description>