Answer: blow fly larvae; either
Phormyia regina (black blow fly) or
Cochliomyia macellaria (secondary screwworm)
This was a tricky one given the somewhat overlapping features of these two species' third instar larvae. If you follow the CDC's pictorial key, you get to the following branch point where you have to decide if:
1. There is a clearly visible button
2. The walls of the slits have lateral swellings
Having examined the maggots myself, I can say that the button is present, but not very distinct, and I believe I see faint lateral swellings on the slides. Therefore, my interpretation is that this is
Cochliomyia macellaria. Here is my best attempt to capture these diagnostic features:
There is little clinical difference between
P. regina and
C. macellaria. Both can colonize the wounds of livestock and humans and feed on dead tissue. Fortunately neither feed on living tissue and therefore don't pose the same risk to livestock as the primary screwworm,
Cochliomyia hominivorax, which has been eliminated from the United States using a sterile fly release program. Of note,
C. hominivorax recently made a comeback in the Florida keys, necessitating a renewed sterile fly release program to eliminate the population. The University of Florida Entomology and Nematodology Department has a nice educational piece on the primary screwworm that you can read
HERE.
Thanks to all of my entomology-minded colleagues who took the time to write in on this post!
1 comment:
Great challenge and images. Sometimes, I find it useful to shave off the terminal segment and clear it in KOH or lactophenol, then slide mount and examine the spiracles. That may offer a better view of fine features.
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