Indonesia – Putting the Fun in Fungus

Written by and Photos Courtesy of Benjamin Maples

This summer I joined an eight week expedition to Indonesia with Operation Wallacea. While I spent some of my time joining the ‘usual’ monitoring surveys, I also devoted as much time as possible investigating the fascinating and poorly-studied invertebrates found in the area. I was incessantly looking for, and taking pictures of, as many insects and other strange creatures as I could on the islands of Kabaena, Buton and Hoga – in total I took about 2800 photos on my trip.

During my explorations, I found something that has piqued the interest of the Opwall forest staff: Endoparasitoid fungi of arthropods which alter the host animal’s behaviour to make it climb and cling to a higher position, then kill the host and sprout fruiting bodies. Perhaps the most well-known example of this is the genus Cordyceps – David Attenborough narrated a well-known documentary involving them (which can be found on Youtube) – but there are other such genera, and I am no mycologist; I cannot identify them (though I bet some of them were Cordyceps). They are interesting, though; according to Tom Martin (Opwall Indonesia’s Lead Scientist), fungi with this peculiar lifestyle had not previously been recorded on these small islands. At his request, I show them off here.

Here is such an endoparasitoid fungus on what appears to be a Hersiliid spider, the first one I found. I saw three of these infested spiders on the bark of two nearby trees in Teomokole, Kabaena, on 24 June.

I cannot even tell what sort of creature lies underneath this pile of fungus. Maybe some sort of hemipteran, like a scale insect? I saw this near the forest camp in northwest Buton on 2 July.

Another set of fruiting bodies on a moth, at a bridge near the forest camp on 3 July.

I found another instance of endoparasitoid fungus on Buton, an orange one spiking out of its indecipherable host, but I neglected to take a photo since it was on one of our transects, and we tended to hurry along faster than my usual stop-and-stare-at-everything pace.

I was able to watch the growth of a Cordyceps in action. On 6 July, alongside the river next to our forest camp in northwest Buton, I found this:

This is a very dead ant (possibly genus Polyrhachis), clinging tightly and stiffly to the edge of a leaf with its mandibles. It had no apparent fungus growing out of it, but I had my suspicions, and returned daily over the next week to see if anything came out of it.

It did. Four days later, on 10 July, you can see some white, hairy stuff coming out of the ant’s joints where it was not before, most obviously behind the head and on the ‘knees.’ This may not seem like much, but it can take weeks for a Cordyceps fruiting body to fully emerge and spread its spores. I was fortunate to catch this one right on the cusp of emergence.

Now, on 13 July, you can clearly see much more fungal hyphae coming out of various openings on the ant, including between abdominal segments. If I had stayed much longer, I might have been able to see the fungus grow from its initial hyphal forays out of the ant up to fully grown fruiting bodies!

Those are all I found of this phenomenon. I did not find any endoparasitoid fungi on Hoga island, but that does not preclude the possibility of them being found there in future investigations. I was not going out into the forest there every day, after all.

If any readers are interested in my other observations, a collection of my photos and their associated details can be found here:

https://www.inaturalist.org/observations/eccentric_entomophile

I am now in the long process of uploading thousands of photos one-by-one, so not all of my pictures are there yet.