Identifying Allograpta in North America

Allograpta is a genus of hover flies with 2 species common in the US. At first glance they look pretty similar but I think after learning how to distinguish them they’re relatively easy from most observations. And there are a lot of observations of them as they’re very common.

The species are Allograpta obliqua and A. exotica. A. obliqua is common pretty much everywhere in North America, while A. exotica is common mostly in the southern half of the US (I think both are common in Central and South America, but there are lots of other Allograpta species there). Florida also has the very distinctive Allograpta radiata. The most similar genera to Allograpta in North America are Fazia, Sphaerophoria, and Toxomerus.

The most reliable feature to separate the 2 common Allograpta species is a section of the thorax called the katepimeron. In A. obliqua it is white, while in A. exotica it is black. It’s located about halfway between the base of the wings and the base of the middle and hind legs. It's marked with arrows in this image: (note that the face stripe mentioned there is not reliable for separating them).
Here are photos of each species as well to compare:

Unfortunately most observations don’t show the katepimeron, but they almost always show the abdomen pattern. There are some features there that can generally be used to separate the species (copied from here):

  1. 2 narrow yellow bands/triangles near the base of tergite 2 (basically the very base of the abdomen) narrowing out towards the centre (present in obliqua, absent in exotica so that the base of T2 is all black).
  2. Narrow yellow band along the entire base of tergite 4 (obliqua has it, exotica does not).
  3. The “leaf-shaped” spots on the side of tergite 4 are usually closer to parallel to the centre pair of stripes, whereas in exotica they are usually closer to 45* or more away from them (exotica also has these spots connected to the centre pair of stripes like this more often, but both can have that).
  4. obliqua seems to often have more orangey-yellow stripes, whereas exotica often has more creamy or whiter yellow stripes.

That probably sounds complicated, but once you get an idea of what it looks like it’s not that bad. Just try to make sure most of those features are in alignment. The first image is a pretty clear A. obliqua, while the second one is a pretty clear A. exotica:
They are variable and there are some that are intermediate, but I think most are identifiable. You can get an idea of the variation possible within each species by looking through their image galleries:
Allograpta obliqua
Allograpta exotica

And finally, in Mexico 3 more species have been observed on iNaturalist:

If you’re interested in helping identify these, here is a filter for all Needs ID observations of the genus in Canada and the US:
Or all of North America:
If you want clarification on anything, please don’t hesitate to ask here or tag me in an observation. Feel free to skip over any that you’re not sure about. Please also let me know if I should correct anything here.

(copied for the most part from this forum post)

由使用者 upupa-epops upupa-epops2019年12月19日 16:17 所貼文


Thank you very much, Caleb!

發佈由 raycama 超過 4 年 前

Extremely helpful explanation; thanks!

發佈由 laurenjansensimpson 超過 4 年 前

Thank you for the nice guideline, it is easy to follow and helpful :)

發佈由 melissadilara 約 3 年 前


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