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 he has the right family. Workers 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 different genus, Cynomya. They failed to first determine the correct genus before keying 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, 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 interspecific variation in a 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 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.
Summary of updates to blow flies of North America keys
Since I published my 2006 paper "Keys to the genera and species of blow flies of North America north of Mexico," it has been relied upon by many researchers to key North American blow flies and I have received numerous comments and questions about it. Following are some tips to aid those using this key. Feel free to contact me if you find a new error or have a question. This key with these corrections included can be found in the book “Forensic Entomology, the utility of arthropods in legal investigations” edited by Jason Byrd and James Castner. The key and corrections in Spanish can also be found in my literature list.
Tips For Using The Keys More Effectively And Errata
Keys to the genera and species of blow flies (Diptera: Calliphoridae) of America North of Mexico. 2006. Proceedings of the Entomological Society of Washington. 108(3): 689-725.
These changes are incorporated in the version of my key in Forensic Entomology edited by Byrd and Castner, see my literature list.
P. 697. Keys to Genera. Couplet 13 separates the genus Lucilia from other genera. The second half of couplet 13 states abdomen metallic blue with whitish microtomentum, but Cynomya and Cyanus both have shining abdomens with no whitish microtomentum which is similar to Lucilia. However, you can still separate these genera from Lucilia because the thorax of each genus (Cynomya and Cyanus) is covered with whitish microtomentum while it is not in Lucilia.
P. 697, Couplet 15. Separating species based on calypter color can be confusing, because species that fall in the “dark” category vary from light to dark brown. Sometimes the margin is white, but the center is always, at least, light brown. Most of the species with “white” calypters are rarely collected (except Cynomya) and occur only in the far north or at high elevation. White calypters sometimes darken in specimens killed in alcohol or left in kill jars too long. In Cyanus the upper calypter often has a light tan margin, but a white center, the lower calypter is all white.
P. 699 Couplet 4. Calliphora latifrons has an orange anterior spiracle which will help separate it from most of those Calliphora found later in the key. The exception is C. vicina which also has an orange anterior spiracle. Also note C. grahami, which comes earlier in the key, has an orange anterior spiracle.
Couplet 6, says the genal dilation of C. coloradensis is reddish, but only the anterior half to two-thirds is reddish.
P.716, Fig. 84, the left side of the sketch (male Pollenia angustigena) shows the density of setae on the venter of the abdomen, but it is drawn too sparse. It is about twice as dense as shown, but still much sparser than in male P. rudis.
P. 718. Couplet 2. Palp black or brown versus orange or yellow - specimens with light colored palps can be confusing as they darken in specimens killed in alcohol or left too long in a kill jar. Check other characters before confirming ID.
P. 719. Couplet 8. In my key, it was difficult to separate female Lucilia cluvia from L. coeruleiviridis. The following character works for both sexes. In L. cluvia the color of the setae on the gena is pale along the rear 1/3 to 1/2. In L. coeruleiviridis the setae on the gena are all dark. Note however, the postgena of both species has pale setae. See Whitworth (2010) on West Indies blow flies where this character is illustrated.
P. 722, There were several errors in the section on Pollenia griseotomentosa. I stated that Rognes listed Pollenia griseotomentosa from Ontario, Canada in his 1991 book, but that was incorrect. He actually verified the specimen from that location in 1997 and relayed this information to me via personal communication. Under couplet 5, I listed P. griseotomentosa from the Northwestern U.S. and Wisconsin, based on the absence of the outer posthumeral seta. However, I have since concluded these specimens were aberrant P. angustigena, not P. griseotomentosa. I have subsequently verified this species from Newfoundland, British Columbia, New York and Pennsylvania. See Jewiss-Gaines, Marshall and Whitworth (2012) for further information.
Errors in the Literature cited:
P.725, For Shannon, R.C. 1926. the correct pages are 115-139.