Scalmogomphus revisited - a dream or a nightmare

Although late in the season for gomphids, we had our eyes open at the gold-diggers stream in Pia Oac this Saturday October 4 because the sun was out. Indeed, two male Scalmogomphus chased each other and then perched on the rocks. Catching them is a priority, as there is a mystery to be solved here: although I have not been able to find consistent differences in males between this location and Yen Bai, the females I caught here have very different vulvar lamina. But lucky for these males, I missed completely when trying to catch them. But a while later I noticed one of them, or another, who knows, perched on top of a bush nearby. I was able to catch it. Still carrying it in my hand, I went back to the stream and noticed another one. This seemed to be very much paler. I decided to try and net that one too and I was successful. As this second one was quite a bit lighter in coloration, I decided to take both home, scanning them would provide nice input on the extremes of variability in the species. So far so good.

Until yesterday evening under the microscope it became apparent that these two specimens are in fact different species, with rather great structural differences in their anal appendages to match the differences in coloration and size.

There has been quite a bit of confusion in the literature concerning some closely related genera in the Onychogomphids. Onychogomphus, Nychogomphus, Phaenandrogomphus and Scalmogomphus share many characteristics and species have been moved from one genus to another time and again. Chao (1990) erected Scalmogomphus for a new species, Scalmogomphus falcatus, on the basis of its peculiar penile organ. In fact, that organ also occurs in two other species that were described subsequently: S. guizhouensis (Zhou and Li, 2000) and S. weshanensis (Zhou, Zhou and Lu, 2005). Onychogomphus bistrigatus was also moved to this genus (Chao, 1990). If so, it is strange that O. schmidti, with a rather similar penile organ, has not yet been included, but remains in Onychogomphus. Onychogomphus dingavani was moved to Phaenandrogomphus by Chao. I have no knowledge of its penile organ, but this is another closely related species.

It is difficult to establish the differences in the literature between the three Chinese species of Scalmogomphus. Drawings are minimal in quality and my Chinese is extremely pour, not to say absent. There are few published photos of certain affiliation, and some on the web are clearly mistaken. It is unclear to me whether these species are true species, or whether, they just represent variants, a result of the few specimens concerned and the inherent intraspecific variability. It is simply hard to judge from the available document.

Do Manh Cuong (2008) redescribed S. guizhouensis, but cautiously states that of course his specimen should be checked against the type. Nevertheless, it is based on this work that I have identified all specimens until now as S. guizhouensis, although there is some variation in color pattern, both as a result of aging and as a result of variability. At least, that is my assumption. Several species may be involved after all.

Nevertheless, the occurrence of two types of females, similar in all outward appearance but the length and shape of the vulvar lamina, was cause for concern. It seemed unlikely that this structural and consistent difference could be explained as intraspecific variability. But no evidently different males could be associated with these long-vulvar females, on the contrary, they occurred together with typical S. guizhouensis males, just like their short vulvar counterparts did in Yen Bai.

The darker specimen of October 4 was in all aspect a normal male, albeit somewhat robust. Total length was 55mm, whereas two specimens I have are 53 and one 55mm. Its bent spoon-like superior appendages are a little more evidently spoon-like in dorsal view than usual. The other specimen was small, 49mm, had a different facial pattern, a small yellow spot between the posterior ocelli, a double yellow band over the occiput, extensive pale yellow on the dorsum of the abdomen, and only a short black streak at the top end of the first lateral suture, normally completely black. The posterior hamule is not as clearly bent at the tip, the superior appendages are not obvisouly spoon-shaped at all, and not as abruptly bent towards the apex. The inferior appendages miss the obvious dorsal tooth near the base, but instead have a more nychogomphus-like shoulder.

Of course it has the typical bifurcate anterior hamule, the anterior branch of which is very long, narrow and hooked at the tip. It also has the typical long posterior lobe to the penile head creating the double jaw wolf head like shape so characteristic of the genus. If Scalmogomphus is a valid genus, its inclusion in the genus appears straightforward.

But all Chinese Scalmogomphus species have the typical basal tooth on the dorsum of the inferior appendages. Their superior appendages are more hooked and spoon-like. In fact they are all so similar in this respect that it is hard to tell them apart. This is why I turned to S. bistrigatus. It is not clear to me whether or not that species always has a clear basal tooth or whether in fact is has more of a shoulder. It appears that the superior appendages are more clearly bent than in the present species, which appears more in between Scalmogomphus and Phaenandrogomphus in this respect. It does have the clear dorsal tooth towards the apex, typical of Scalmogomphus. On the other hand, it has even less black along the lateral suture than expected and the humeral and antehumeral stripes are connected dorsally, something more reminiscent of Phaenandrogomphus dingavani.

Having said that, S. bistrigatus has typically a yellow spot between the posterior ocelli and it has a yellow occiput divided into two by a thin blackish line, exactly as in the specimen. It also has a straighter posterior hamule compared to the other species. And surprisingly, the female has a characteristic that sets it apart from all others in the genus plus P. dingavani. It has extremely long and pointed vulvar lamina, reaching until or past the posterior margin of S10. The confusion in relation to this characteristic was solved by Fraser (1937) and illustrated by Asahina (1988).

The combination of the long-vulvar females and the occurrence of a clearly different male with character traits of Scalmogomphus bistrigatus is quite suggestive. The females have however not been seen in close association with the male. In fact the females of the males of S. guizhouensis have also not been seen in association with those males. They have not been seen at all. Long-vulvar females visit regularly to oviposit. Apparently copulation takes place away from the stream. No short-vulvar females have been observed, even with normal males regularly taking up position on rocks along the stream.

All this offers alternative possibilities: 1) The long-vulvar females in fact are the females of the "typical" males present, which is in that case not S. guizhouensis, but a dark variant of S. bistrigatus, and the a-typical male is a species novum, 2) The long-vulvar females are the females of the a-typical pale male, which in itself may be paler than average, both displaying characteristics of S. bistrigatus, but the male slightly odd, and thus better named S. cf. bistrigatus, or 3) The females are S. bistrigatus, the typical males S. guizhouensis, and the a-typical male is a species novum. For the moment option 2) seems best suited as working hypothesis.

I invite any criticism or suggestions to further help solve this problem.

On the left typical Scalmogomphus guizhouensis, on the right the somewhat smaller, more brightly colored Scalmogomphus cf. bistrigatus. Note also the bright yellow costa.

Top S. cf. bistrigatus, bottom S. guizhouensis. Note the very apparent differences in angulation of superior appendages.

Male Scalmogomphus cf. bistrigatus. Note Phaenandrogomphus/Nychogomphus like appendages and the connected humeral and antehumeral stripes

Male of S. guizhouensis

Long-vulvar female, S. bistrigatus (see also other blog entries on the females)

Facial pattern of S. cf. bistrigatus, with yellow dot between posterior ocelli, yellow occiput and yellow line over postclypeus

Facial pattern of S. guizhouensis, yellow much reduced, black occiput

Appendages on S2, note extremely long and thin anterior hamule anterior branch (extreme right in the picture) and "wolf-jaws" of penile organ (upside down) of S. cf. bistrigatus

The same for S. guizhouensis. Wolf-jaws partly covered in muck, apex of posterior hamule curved

Ventral view of the anal appendages of S. cf. bistrigatus. Note color, small row of denticles on apices and lack of spoon-like appearance

Same for S. guizhouensis. Note the distinct spoon-like shape.

Lateral view of the appendages of S. cf. bistrigatus. Note lack of basal dorsal tooth to inferiors, replaced by shoulder, and gentle curve of superiors. Inferiors and superiors squeezed together as distortion due to heat of microscope's lamp, normally more separated (see scan of lateral view for normal situation). Color a little light due to use of flash, but closer to nature than of photos with microscopic lens below.

Dorsal view of appendages of S. cf. bistrigatus. Inferiors look shorter due to squeeze described above.

Lateral view of appendages of S. guizhouensis, showing clear basal tooth and strong hooked aspect.

Dorsal view of the same. Spoon-like dilation shows in dorsal view as small flap. This is not visible in most specimens.

The Scalmogomphus mystery

This spring, on May 10 and 11, I saw many Scalmogomphus guizhouensis in the Yen Bai area. After that upon other visits to the same area I did not see them anymore. This made me think it was a species that only flies early in the season. To my surprise this proved incorrect. On July 3 and 4 I passed through Yen Bai Province again and this time found fully mature males sitting on rocks in the middle of streams or on bushes nearby. I also saw a female. Nothing was different in their structural appearance from the May specimens.

Afterwards I visited Pia Oac Nature Reserve in Cao Bang Province and posted for a long time at a spot where a larger stream exits from the woods into the open, because I had observed a Sieboldius species there that I hoped to check. On 7, 8 and 9 July time and again female gomphids came to that exact spot and hovered in the middle of the stream while dropping eggs. After I was able to catch one two very interesting things became apparent. The first was that this female had very long vulvar lamina, not just long, but also extremely pointy. The second that the thorax pattern was slightly different, but that otherwise they seemed exact copies of female Scalmogomphus guizhouensis. Subsequent females that I caught all had the same lamina. It was thus not a freak occurrence. I did not see any males, but on the third day I finally was able to first take some pictures and then also catch a male. To my disappointment I could not find any structural differences between these males and the Yen Bai males of Scalmogomphus guizhouensis. It is very unlikely that these males, caught at the exact spot where the females came to oviposit and with one male observed to chase one of the females, and with all females present consistently showing the extremely long lamina, belonged to one species and the females to another. But how then to explain the consistent structural difference in the females. In fact I took photos of one female with the thorax pattern almost the same as those from Yen Bai, so the only difference consisted of these long vulvar lamina. What does this signify? With the males exactly the same it is hard to claim it as a different species. But what then? A different subspecies? And if such obvious structural differences have no value to separate different species, what does that mean for other species that have been described based only on females that are structurally different from other females.

4 species of Scalmogomphus have been described, but the differentiating characters are not always clear. In none of the descriptions I have found reference to extremely long and thin lamina of the female. Below the strange and obvious difference is illustrated, together with the otherwise great similarities.

Scalmogomphus sp from Pia Oac. This is the specimen closest in thorax pattern to the specimens from Yen Bai. Clearly the extremely long lamina can be seen, reaching past S10.

Another Scalmogomphus sp from Pia Oac, with typical reduced black line over metepisternum. The extremely long lamina can again clearly be seen.

Female Scalmogomphus guizhouensis from Yen Bai. Extremely similar, apart from lamina.

Because this is the lamina found on females in Yen Bai. Rather robust and falling short of the distal margin of S10.

Whereas this is the lamina on the females from Pia Oac, thinner, and especially longer, reaching past distal margin of S10.

In lateral view, this is especially evident

This is a male Scalmogomphus sp caught in Pia Oac

And this is a male Scalmogomphus guizhouensis from Yen Bai. Under the microscope appendages and outward appearance of organs on S2 are identical.

Another male from Yen Bai

Another male from Pia Oac

And yet another male from Yen Bai

Scalmogomphus guizhouensis in Yen Bai

The weekend of 10 and 11 May I visited Yen Bai Province looking for dragonflies and escaping the hot (41 C) weather in Hanoi. The Saturday was mostly cloudy, but around Nam Bung and further on along the QL32 it was still great exploring. I ran into about 15 quite colorful gomphids that I could not identify. Both males and females were common and quite easily approached. At home, after some searching, I finally identified it as Scalmogomphus guizhouensis. In fact, to be fair, I identified it as S. wenshanensis. The latter was described in 2005 by Zhou, Zhou & Li. The former in 2000 by Zhou & Li. Scalmogomphus guizhouensis was redescribed based on a collected individual from Sa Pa by Do Manh Cuong (2008). I found almost no difference between the two species when comparing the drawings. Interestingly, Zhou, Zhou & Li make no mention of S. guizhouensis, even if one of the authors also described that species. They only compare it to S. falcatus and the grounds on which they do so (second tooth apically on inferior appendage, bifurcate anterior hamule) are shared between both species. Only the green stripe on the frons is cut in two by black line in the middle in S. wenshanensis. Be that as it may, the species is identical with the redescription by Do.

Male Scalmogomphus guizhouensis

The same, female

Another male S. guizhouensis

Another male

The female in the field

Apart from the bifurcate anterior hamule, also the appendages are typical, with the strongly downward hooked superiors and the inferiors with two teeth, one at basal third and one close to the tip