|The color and size range of Lucilia coeruleiviridis is amazing, from blue to green, even bronze. The absence of certain little hairs and other traits unite these guys and gals.|
... but not your home. This is about the many dead specimens of blow flies (Calliphoridae) that take up residence in the North Carolina State University Insect Museum.
It all started one day in December when I came across a lovely blow fly resting on the side of the university parking deck. I couldn't help but capture it in the little bag I keep in my wallet - it would make a great subject for photos once I got into the clinic! After settling in and letting the fly calm down under a container on a piece of white paper (a tried and true technique), I snapped some pictures:
|Male Chrysomya megacephala have different sized facets on the top and bottom of each eye.|
Looking in the three drawers of blow flies we have in the museum using our online GigaPan images, I found not a single specimen of the fly that just got away! In fact there wasn't even a tray for the genus Chrysomya. This had to be rectified. So my project for the winter was to organize the drawer and a half of unsorted specimens to see how many species we might have, awaiting identification.
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When the samples started to slow down in the clinic around January, I walked upstairs to retrieve the drawers of potential treasures. My first step was to find the main literature on identifying blow flies. Luckily, I knew they were a relatively small (84 species in the continental US) and easily identified group, in part because of their importance to humans and animals. Terry Whitworth's key to the genera and species of most of our blow flies served me very well, as did the very nice web key put out by the Canadian Journal of Arthropod Identification. I also knew there were some exotic specimens and luckily a few were covered in the generic key in the Manual of Central American Diptera Vol. 2.
After finding the means to sort through the flies, where would I start? First I got rid of all the obvious non-blow flies, mostly other calyptrates (Tachinidae, Muscidae, Anthomyiidae and Sarcophagidae), but also some shiny Syrphidae.
I didn't want to tackle the two most common blow fly genera (Lucilia and Calliphora; see below). So next I started grabbing out the most obvious: the striped ones! I am talking about screwworm flies (Cochliomyia). The primary screwworm, Cochliomyia hominivorax, is considered to have been eradicated from North America since 1966. It was eradicated because its larvae infest and damage healthy tissue in both animals and man, sometimes leading to death. This is certainly a fly we don't want around. I didn't find any specimens of that species in the unsorted material, but did find many of its common, close relative the secondary screwworm, C. macellaria. These differ greatly from their medically and veterinarily important cousins, in that they only feed on rotting carrion (so unless you're a zombie, there's nothing to be worried about).
|A male primary screwworm fly (Cochliomyia hominivorax) tagged for research.|
Peggy Greb, USDA Agricultural Research Service, Bugwood.org
At this time I also noted many other specimens with dark faces and dark blue/green bodies, which turned out to be black blow flies (Phormia regina). They made up a large portion (114 specimens) of the material I was looking at, so once they and the Cochliomyia (64 specimens) were sorted out it looked like I was making progress.
Now I felt like Neo from The Matrix: which color pill do I take? In front of me was a sea of large blue flies interspersed with equally as many green or copper flies, all with varying degrees of shine. I decided to go with the smaller green ones that I assumed were all Lucilia, the very common green/bronze blow flies. Most people are familiar with these since they enter homes in search of rotting meat on which to lay their eggs. They are also commonly used in post-mortem forensics (along with other blow flies that feed on remains). Some are even used in maggot therapy - the process where maggots are applied to a wound and feed only on the decayed, bacteria-ridden tissue, effectively cleaning the wound and allowing it to heal properly. If you've seen the epic movie Gladiator you know what I am talking about (and it is still used today).
|Green bottle/blow flies (Lucilia) have a blue-green or coppery bronze appearance and are commonly encountered.|
Most (174 specimens) of this genus turned out to be Lucilia coeruleiviridis (see title picture), while we also had some L. cuprina (26 specimens), L. sericata (59 specimens) and L. illustris (20 specimens). The most interesting was one specimen of Lucilia silvarum. The species was formerly placed in the now defunct genus Bufolucilia, whose name relates to the fact that females have a habit of laying eggs on toads (genus Bufo) or frogs. The larvae hatch and bore into the amphibian's skin, sometimes in the nose or eyes, and often kill the host. Truly grotesque (for those who are not squeamish, here is what it can look like).
Not all small, metallic green flies were blow flies, however. Among the Lucilia were some impostors, most of which (51 specimens) were a species called Neomyia cornicina. This member of the family Muscidae breeds in cattle dung and, although very similar, has some small differences including a much more metallic face and only one pair of postsutural acrostichal bristle (all blow flies have at least two pairs).
Now onto bigger and bluer flies: Calliphorinae! This group includes the largest blow flies around. Most are dull to shiny blue with some golden or silvery areas on the head or abdomen, and are carrion feeders (though will also come to dung).
|Calliphora (like this C. livida) are large, blue blow flies that are often are the loudest flies buzzing inside homes.|
I found a number of Cynomyia cadaverina (45 pretty blue-green-purple flies with an ominous name) and a single specimen of Cyanus elongatus, which I was happy to add as a new species to my favorite website Bugguide.net (specimen here). Most of the large blue flies, though, were one of several species of Calliphora, of which the following species (specimens) were identified: Calliphora stelviana (2), Calliphora aldrichia (1), Calliphora latifrons (3), Calliphora vomitoria (12), Calliphora vicina (74), Calliphora terraenovae (9), and Calliphora livida (7).
The last group of blow flies to receive my attention, also happens to be the oddest of the bunch. Cluster flies (Polleniinae: Pollenia sp.) are dull brown or gray with lots of crinkly golden hairs on their thorax - very different from their metallic brethren:
|A male cluster fly (Pollenia sp.) resting on a leaf. Note the golden hairs on the thorax, diagnostic for the genus.|
Unlike most other blow flies that mainly feed on carrion or dung, cluster flies are parasites with an unusual host: earthworms! Females lay eggs on the ground where earthworms are present. The young larvae are able to attach to and penetrate the worm to feed on its insides, all the while sticking its back end out of the host to breathe. Sometimes multiple specimens infest a single host, though this can lead to the death of all parties involved. Cluster flies are also known for entering homes in the fall to overwinter, as discussed previously on this blog. Pollenia in the US were traditionally treated as a single species, P. rudis, but more recently have been divided into a several species. I took all the specimens labeled as P. rudis and all the unsorted specimens and found the following three species (specimens): Pollenia rudis (73), P. pediculata (28), and P. angustigena (33).
And what about those Chrysomya? Well, I ended up finding four specimens of the species (C. megacephala) that got away and another two specimens of the other species, C. rufifacies. So at least we have a few, and I will be sure to collect more when I see them.
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All together I looked at over 800 blow fly specimens and added 11 species previously unidentified for the collection. Many were from NC, but there were also some from the North or out West, and good series from Alaska. We also had one specimen of Hemilucilia segmentaria from Costa Rica, new for our collection. The oldest specimens (but still surprisingly pristine) were collected in the early 1900's, some even by our most famous entomologist Clement S. Brimley (who together with his brother, Herbert H., helped found and grow the NC Museum of Natural Sciences).
I hope to do this for other groups in the museum as it serves many important purposes. Specimens are easier to find for loaning to researchers and we have a better idea of what holdings we have. We can also better organize the little insects on pins to free up room for more specimens. On a personal note, doing these identifications gives me practice with these groups and allows me to see the literature and types of features that are used to identify them.
Maybe I'll tackle the crane flies next...only 15,000 species in the world!
Keys to the genera and species of blow flies (Diptera: Calliphoridae) of America north of Mexico (2006) T.L. Whitworth. Proceedings of the Entomological Society of Washington 108: 689–725, 2006: http://www.birdblowfly.com/images/Publications/Keys.pdf
Blow flies (Diptera; Calliphoridae) of eastern Canada with a key to Calliphoridae subfamilies and genera of eastern North America, and a key to the eastern Canadian species of Calliphorinae, Luciliinae and Chrysomyiinae (2011) S.A. Marshall, T. Whitworth, and L. Roscoe. Canadian Journal of Arthropod Identification No. 11, 11 January 2011, available online at http://www.biology.ualberta.ca/bsc/ejournal/mwr_11/mwr_11.html, doi: 10.3752/cjai.2011.11