Preamble: The fly family Chloropidae (the frit flies or grass flies or eye gnats) is one of the most geographically widespread, abundant, species-rich, and ecologically diverse families of flies on Earth. Although almost 3000 species have been described, and some species are pests of crops, livestock and humans, we still have much to learn about the taxonomy, natural history, and phylogenetic relationships of chloropids. They’re also my favorite group of flies.
We’ve just published a new paper (see Wheeler and Solecki, 2013 in Publications) in the excellent journal Zootaxa, in which we describe three new species of chloropid flies from South Africa. That, in itself, isn’t terribly big news — there are likely thousands of undescribed species of chloropid flies, and the African species are particularly poorly known. So, in order to make this post marginally more interesting, I’ll mostly talk about the weirdest of these new flies.
All three new species are in the genus Calamoncosis, a group that is most diverse in Eurasia, although a few species have recently been recorded in North America. Most species of Calamoncosis whose natural history is known feed, as larvae, in grasses, either on their own or by invading the galls made by other chloropid flies. Prior to our study, there were only two species of this genus known in Africa. Our three new species not only more than double the number of species known from the continent, but also give a little insight into just how many more species of this group may remain to be discovered from that continent. Why? Because specimens of all three of our new species were collected in one place, on the same dates, in one single Malaise trap. Imagine how many more species might be out there in other places, waiting to be collected in other traps, by other keen collectors.
The giant head below belongs to a male of Calamoncosis unicornis. It’s a weird fly. I’ll explain why.
Most higher flies (the group that chloropids belong to) have a pretty typical antenna. In plain language, there are a couple of little segments at the base, a bigger, round segment (the first flagellomere) and a bristle-like section (the arista) sticking out of that big round segment. House flies have that. So do fruit flies. And blow flies. And almost every chloropid fly that we know of. Except Calamoncosis unicornis and one unrelated species from Japan.
Calamoncosis unicornis males have no arista, just a tiny stub that’s only visible under very high magnification. Having no arista is a potential problem for a fly because the arista plays a pretty important role in sensing and detecting the world. Deprived of some of its important senses, a fly will have some serious issues. So, apparently to compensate, the male of Calamoncosis unicornis has evolved an extremely long, and very hairy, first flagellomere (it’s that big thing sticking out to the left in the top photo) that may take over the sensory functions of the arista. There are a few other flies in which the arista is missing, and in most cases the first flagellomere is also enlarged and hairy, so this seems like a common solution to the challenge of life without an arista. Another interesting thing about Calamoncosis unicornis is that this weird antennal modification occurs only in males; the female has a fairly normal chloropid antenna.
I know of only one other chloropid fly that has such strangely modified antennae — a Japanese species called Kurumemyia ongamea. But the situation is reversed; the male has normal antennae, and the female has no arista but a very large and V-shaped first flagellomere.
So the obvious question is: Why? What sort of evolutionary pressures could lead to this weird modification in antennae in these two species of a very large family? And why only one sex? And why the male in one species and the female in the other? The answer, as with many other questions about insect evolution, is: We don’t know. Many insect species are described only from preserved museum specimens; they have never been observed alive. This means that we often know little or nothing about how they actually live their lives, or use their sometimes strangely modified body parts. Taxonomy — giving names and identities to new species — is only the first step in really understanding the lives of insects. Once we can attach a name to a species, we then have a framework for exploring and describing their natural history, behavior, morphology, interactions, and more. But we’ve only really done that for a tiny fraction of insect diversity. Lots of mysteries remain. And lots of great reasons to get out there and explore the world of little, under-appreciated, flies.