Using Keys Effectively

Many misidentifications result from workers using keys improperly. Inexperienced users often jump to conclusions about what they are keying. A common problem, for example, is attempting to use calliphorid keys to identify metallic muscids. They are superficially very similar to blow flies, but muscids lack meral setae, while calliphorids have them. The key user should first verify they have the right family. They also often assume they know the genus and don’t run the specimen through the genus key. Several entomologists have sent me specimens of what they thought were Calliphora because they did not key properly with my keys. When I examined the specimens, I immediately realized they weren’t Calliphora at all, but a similar genus, Cynomya. They failed to first determine the correct genus before trying to key to species. Always make sure you have the right family and genus (or even order) first.

Another serious mistake is to skip couplets in a key, because you are sure you know where a specimen belongs in the key. In my Calliphora keys for North America 2006, the first 3 couplets address rare species. If you skip to couplet 4 where more common species start, you may miss a rare species and misidentify your specimen.

Anyone who wants to become an expert at identifying species in an insect group should develop a reference collection. This collection should have numerous specimens exhibiting intra- and interspecific variation within and between each known species that has been positively identified by an expert. Beginners often get bogged down by variation within and between species. Until you learn the range of variation in a group, this can be a problem. The other common challenge for taxonomists is keying poor quality specimens which are often distorted, damaged, or discolored. With experience, you can accurately identify most specimens, no matter what their condition, as long as important characters are present. Also don’t ignore factors like “known range” for species which can help you narrow down the probable species to choose from. Recently I was sent a “rare African blow fly species” that had been found in the United States. It was a common North American muscid, not a blow fly. Occasionally an exotic species is discovered in a new location, but, in my experience, it is more likely to be mistaken identity. However, you never know until you have properly keyed it.

For researchers struggling to identify species with traditional keys, I recommend our recently published pictorial keys to the blow flies of North America, the link is http://dx.doi.org/10.3752/cjai.2019.39 (Jones, Whitworth &Marshall 2019). This key includes a variety of updates to my original keys published in 2006. Key users are welcome to contact me at blowflies@twhitworth.com for help keying specimens.

Article:

Blow flies of North America: Keys to the subfamilies and genera of Calliphoridae, and to the species of the subfamilies Calliphorinae, Luciliinae and Chrysomyinae - Click Here To View The Complete Article

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Terry Whitworth, Ph.D.
Entomologist
3707 96th ST E
Tacoma, WA98446
Phone 253-531-7925
email: twhitworth@blowflies.net