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The Fat Coneheads of Gorongosa

12 Setembro, 2013

By Piotr Naskrecki - A few years ago I was at the Museum of Natural History in London to examine several type specimens of African katydids. One of them was the holotype of a conehead katydid Lanista africana, a species described by the infamous 19th century entomologist Francis Walker. (Stories abound about the quality of his taxonomic work, such as the time when he described the same set of insect species twice, each time giving them different names. This, of course, is not unusual and happens to this day, but in his case it was the same box of specimens which he first described in the morning, and then again after lunch, without realizing that he had already given them names.) What caught my eye was an inscription on the label attached to the specimen. In addition to the typical 19th century exactitude in the locality information (“From Africa”) it bore the following note – “Lived 18 months without food.”


Photo: Conehead katydid Lanista annulicornis (a.k.a. L. africana) showing its huge, sharp mandibles designed for cutting and crushing grass seeds. They also do an admirable job on human skin.


Now, without getting into speculations as to why anybody would torture a poor katydid for so long, I was of course highly skeptical about the veracity of such a statement. Eighteen months? That seemed unlikely, to say the least, considering that the average lifespan of an adult katydid is only a few months. But that was before I had a chance to see a live individual of Lanista.


Photo: The body of the conehead katydid Pseudorhynchus pungens looks just like a blade of grass and few predators can spot them.


Gorongosa National Park is defined by its extensive grasslands and woodland savannas, just the kind of habitat that African conehead katydids love. If you walk through the tall grass here (and you better have an armed ranger with you if you decide to do so – it is surprisingly easy to miss an elephant hiding a few feet away) chances are that the first insect you see will be a conehead katydid scurrying away. Fourteen species of coneheads can be found here, and one of them is the aforementioned Lanista africana(Which, incidentally, is now known as L. annulicronis. Shockingly, L. africana turned out to be a synonym of L. annulicornis, a species described earlier by – who else? – Mr. Francis Walker.)


Photo: Conehead katydids’ mortal enemy, the Black-bellied Bustard (Lissotis melanogaster) – I have watched this bird slowly walk in tall grass and expertly pick katydids and grasshoppers that were invisible to me.


When I caught my first Lanista I was surprised at how fat and heavy it felt. Since I needed to preserve a few specimens of this species for the Gorongosa synoptic collection and my own work, I dissected them and discovered that their entire body was absolutely loaded with fat tissue. It was difficult to discern any internal organs in the abdomen because the layer of thick, white fat filled every bit of space – these guys were in a serious need of liposuction. All katydids that I had seen up to that point were rather lean – where did all that fat come from and why did they have it?


African coneheads, as opposed to their New World counterparts, are almost exclusively herbivorous, and the food that they are particularly fond of are grass seeds. Grass seeds are loaded with carbohydrates and lipids, and if you can feed on them effectively you will start storing fat very quickly. (That tasty Big Mac that goes straight into your hips? It is mostly the bun – pure carbs – that does the damage.) Coneheads’ mandibles are seed grinding machines, very sharp and propelled with powerful muscles – this is why coneheads have such huge, elongated heads. Few insects are as good at stripping the husk of a grass seed and getting to the tasty kernel as a conehead katydid.


Photo: The genus Ruspolia is represented in Gorongosa by at least six species, some of which may be new to science. R. consobrina is one of the few katydids that are routinely eaten by people in Africa.


Grasslands in Africa are seasonal – the seed bonanza of the rainy season quickly turns into near starvation of the dry one – but if you can store enough energy to survive those few very lean months then your chances of producing the offspring at the onset of rains, perhaps even a second generation of the species in the same year, are greatly improved. I strongly suspect that this is what the coneheads of Gorongosa are doing. The individuals I am seeing now, at the peak of the dry season, are significantly thinner than those I saw here just a few months ago, but I believe that they belong to the same generation. And while I am not going to test it, I now find it more believable that an individual with all its fat reserves intact may be able to survive for a very, very long time without food. And, incidentally, the one species of katydids that is routinely eaten by people in Africa is a conehead Ruspolia consobrina, whose body also contains high levels of nutritious fats.


Photo: The large, elongate head of the conehead katydid Pseudorhynchus hastifer hides powerful grinding muscles and helps this animal blend in among blades of grass.


Read more on Piotr's blog The Smaller Majority