More artists need to use iNaturalist.org for nature art refs. The site is organized taxonomically & geographically. i.e. You can search "Canis" for wolves, but "Canidae" gives you all canids to compare differences. You can also browse by location to see what kind of plants live in specific places.

For invertebrates (which are generally harder to find pics of online) I specifically curate photos showing clear close ups & weird angles that are normally hard to see. All images included here are included with the photographers' consent. www.inaturalist.org/observations...