Morphological characters have a molecular basis. The characters we can see are the products of genes and proteins. Structural differences are the products of gene or protein differences. Postive identification can just as well be based on molecular characters as morphological characters. A group of scientists* applied mass-spectrometry (MS) to fleas. MS of extracts from fleas with abdomens removed gave consistent profiles according to speices examined. Profiles of cat fleas and dog fleas are easily distinguished by this method. The MS method works best on fresh specimens and less well on fleas preserved in alcohol. Molecular analysis of flea species could potentially be used as an aid for diagnosing diseases that require a flea vector. Analysis and identification can be done quickly by a technician trained in standard lab techniques. This would be faster than shipping the fleas to a trained expert for identification.
*Amina Yssouf, Cristina Socolovschi, Hamza Leulmi, Tahar Kernif, Idir Bitam, Gilles Audoly, Lionel Almeras, Didier Raoult, & Philippe Parola. Identification of flea species using MALDI-TOF/MS. Comparative Immunology, Microbiology and Infectious Diseases, Volume 37, Issue 3, May 2014, Pages 153-157.