Try Eric Carle. He writes and illustrates children's books, but does
beautiful and creative insects. Also Northern Renaissance Dutch painters did
beautful vases filled with flowers, but when you look closely, there are all
sorts of insects. Claesz comes to mind, but there are others. Picasso
and Franz Marc did wonderful horses, not to mention paleolithic sites like
Lauscaux in France. Marc is very interesting, and I love his blue horses.
Emile Nolde, Van Gogh, Monet, Manet, Cezanne were all taken with nature.
Monet's cypresses in which he plays with synthaethesia are fascinatingl...but
I don't know if they include insects. Can't recall any right off. Bosch
and Heronymous Cock (15th cent) also did really fanastic images, but you have
to be sort of careful what you pick and choose for younger children (that
includes fifth graders). Also Durer did intricate wood cuts and Mauritus
Escher did beautiful wood cuts, many of insects crawling up and and down
stairs, etc. Hope this is helpful.