Are there comprehensive species descriptions on most species?
To suggest a new species, someone must necessarily makes a rather thorough effort of description. A good solution to get some info could be to go to the original paper however, these papers can be very old and hard to find. Also, the standards at that time might be very different from today's. After all, K. Linnaeus managed to describe 13,000 species also maybe because the description were more simple than they are today (see this related post). Andrena hattorfiana was described by Fabricius in 1775 but I could not find the original paper.

Note that the english wikpedia article for A. hattorfiana is relatively decent.

The IUCN red list is also a good source (see here)

The page for the Encyclopedia Of Life is unfortunately a little empty.

Here are some amazing pictures on flickr

You can also just search papers that refer to a given species. Here are a number of papers on A. hattorfiana.