Thursday, February 17, 2011

Sarawak: Maludam Dragonflies

Maludam - as you might expect of a national park protecting a swamp forest and bisected by a river - is a very good place for dragonflies. They were constant companions for Yeo, Kho and I on our river trip, and we turned up a few more in the forest itself. Here, then, to round off my account of our trip to Maludam last May, is an odonate gallery.

This rather stocky little damselfly was very common along the river. This one decided that our boat made an ideal perch. It is probably a male Libellago hyalina, a common member of the jewel family, Chlorocyphidae.  The male hyalina has a strong purple gloss on the abdomen, though, something I don't recall seeing in this individual.

I realize that there are a number of different families of dragonflies. However, it seems to me that almost every dragonfly I manage to get within camera range turns out to be a member of one family, the Libellulidae (which surely says more about my status as a dragonfly neophyte than it does about the insects themselves). I was therefore gratified in the extreme to finally come across this Ictinogomphus (probably Ictinogomphus acutus), a member of a quite different family, the Gomphidae. [July 2017: confirmed as Ictinogomphus acutus by Rory Dow, who pointed out the reddish colour at the end of the abdomen as a dustinguishing mark; this otherwise uncommon species is apparently common at Maludam).

Gomphids are unusual-looking, at least to me, because they lack one of the libellulids' most characteristic features: huge swollen compound eyes that meet over the top of the head. In gomphids the compound eyes are small and widely separated, like the eyes of their cousins the damselflies. The swollen tip of the abdomen is another clue that this dragonfly is not a libellulid. Now where are the aeshnids, corduliids, and the other members of the odonate clan?

This dragonfly looks a lot like Ictinogomphus, but it is, in fact, a libellulid -- in fact, a very common one, Orthetrum sabina. Its narrow needle of an abdomen sets it apart from the other common Borneo Orthetrums, but the evolutionary significance of this I cannot tell. Surely it is not mimicking the far less common Ictinogomphus? Mimics, for their mimicry to work, need to be encountered less often than their models, not the other way round -- so, dragonfly experts, what (if anything) is going on here?

Here are some more portraits of Orthetrum sabina, if only to show what a common dragonfly it was.

These bright red dragonflies exhibit the more typical, swollen abdomens of  many libellulid genera. I believe that these are male crimson dropwings (Trithemis aurora). [July 2017: this is Orthetrum testaceum]

We encountered this beautiful little dragonfly not along the river, but in the midst of the forest, where it practically glowed in the narrow shafts of sunlight along the trail. It is a male Brachygonia oculata, one of the smaller libellulids in southeast Asia, and I think it is one of the prettiest and daintiest dragonflies I know.

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