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As information regarding New World screwworm (NWS) spreads, it’s important to stay up to date on what’s happening in Louisiana. This guide is intended to help provide some quick information to better assist you with rapid identification requests. Be sure to continue to monitor the AgCenter website for up-to-date information on NWS.
The key distinguishing feature with New World screwworm is the black stripes on the thorax. We do have a few common species that might add to the confusion. Secondary screwworm fly (which does not feed on living tissues), is incredibly abundant in Louisiana and looks very similar to New World screwworm. The key difference between these two will be the coloration. While this is not a comprehensive list of all metallic flies in Louisiana, these will be the most common look-a-likes you will come across.
| Chart Label | Species | Common Name | Thorax Stripes | Color | Notes |
|---|---|---|---|---|---|
| A | Chrysops rufifacies | Hairy maggot blow fly | No | Blue/green metallic | Maggots are very distinct, as they are hairy. |
| B | Phormia regina (Winter) | Black blow fly | No | Often bluish-black metallic, sometimes with shades of green | This is a cold weather species. |
| Chrysomya megacephala (Summer) | Oriental latrine fly | No | More blue metallic, but can have some subtle green | Large red eyes and short, stout body. | |
| C | Sarcophagidae | Flesh flies | Yes | Gray/black and nonmetallic | These are not metallic and are much bigger, but they are common. |
| D | Lucilia cuprina | Bronze bottle fly | No | Bronze metallic | Another common bottle fly. |
| E | Cochliomyia hominivorax | New World screwworm | Yes | Blue metallic | Anything matching this description should be properly identified by a specialist. |
| F | Lucilia sericata | Sheep blow fly | No | Color varies from blue/green to yellowish and bronze metallic | Another common bottle fly. |
| G | Calliphora vicina/vomitoria | European blue bottle fly | Yes | Blackish-blue, dull metallic | The thorax will appear almost black, and the stripes will be subtle. Abdomen has vertical stripes. |
| H | Cochliomyia macellaria | Secondary screwworm | Yes | Green metallic | Very common species in the same genus as NWS. While these do not feed on living tissue, individuals should still save or submit these for proper identification. |
Common flies in Louisiana that might appear similar to the New World screwworm. E is the New World Screwworm. Illustrated by Rodrigo Diaz.
