Monday, December 16, 2013

Mystery of the Amazon (1/2)

[1]
Photos of this structure have been bouncing around the web, leading to rampant speculation as to what constructed them. The structures are about 2 cm across and were found on tree trunks and artificial surfaces.

The first images were taken 07June2013 in the Peruvian Amazon by chemistry grad student Troy S. Alexander (Decapod73 on Reddit) and were posted to the Reddit "What's this bug" discussion forum in hopes of finding some clue to the identity of the creature which made them.

Lots of ideas were tossed around. Aliens? Fungus? Moth? Spider? Alien spider? Moth that got lost?

Later in the discussion, user Julgr posted a picture of one of the structures that they had found on a leaf in French Guiana. They had initially assumed it was a peculiar fungus.


[2]
Since the sightings were at both the western and eastern ends of the Amazon rain forest (green in the figure at right), it is possible that they could be found throughout most of the Amazon. The small size of the structures, paired with the rarity of individuals who would both go looking for and report to the wider world about such finds, readily accounts for the sparse reporting so far.

Hopefully, there will be more sightings now that the whole of the world has heard about this mystery of the Amazon.



Following the wide-ranging conversation about this creature eventually led to the BugTracks Blog, where a tentative ID was suggested of a Cribellate spider. This group of spiders produce a characteristically fuzzy type of silk that is seen in this close up of the fence structure.

According to the Wikipedia, Cribellate spiders fall into 21 families, with thousands of species living in a wide range of habitats. Eight families (Austrochilidae, Desidae, Gradungulidae, Hypochilidae, Nicodamidae, Psechridae, Stiphidiidae, & Zoropsidae) have no known representatives in the Amazon region. Two (Amphinectidae & Eresidae) have some representatives in some of the Amazon region, but not covering the sites where the mystery structure has been found. The remaining eleven families (Agelenidae, Amaurobilidae, Ctenidae, Deinopidae, Dictynidae, Filistatidae, Miturgidae, Oecobiidae, Tengellidae, Titanoecidae, & Uloboridae) are found throughout most or all of the Amazon region and are likely candidate families for our unknown spider.

Going through the various Wikipedia pages for each of the families, along with selected google searches, gives some general family trends for maternal behavior. The Amaurobilidae and Miturgidae guard their eggs in a special brood chamber. The Agelenidae, Filistatidae, Oecobiidae, Tengellidae, Titanoecidae, and Uloboridae guard their egg mass in their hunting webs. The Ctenidae carry their egg mass until the brood is about to hatch, then construct a nursery web.

The Deinopidae and Dictynidae spiders hide their egg mass and leave, which is basically the sort of parenting behavior our mystery spider is acting out. Though our mystery spider could easily represent one of the other Cribellate spider families, I'm placing my bet on it eventually falling into either of these. (I might even extend my bet to place it in the Dictynidae, based only upon the typical body form of the family seems more consistent with how I imagine a spider crawling around to make the mystery structure.)

Fortunately, I'm not an arachnologist with his reputation on the line. I can make statements like this and not really be concerned at how they play out in the end.

According to the National Geographic article on the topic, an entomologist will be traveling to the Tambopata Research Center to track down the maker of the mystery during the winter of 2013. We may soon have more data to work with!



Lacewing eggs. [3]
Another topic relates to what selection pressure would encourage the evolution of such a peculiar structure. Ants are a constant threat to small arthropods in most ecosystems and many organisms have evolved mechanisms to protect themselves from them.

Lacewings place their eggs on long silken hairs, out of reach of ants.
Mimetus notius [4]


Other spider species have been noted to construct elaborate egg defense systems.

The mystery structure is the right scale to act as an ant deterrent. The fence-webbing would tangle and trap a single ant trying to climb over (though a swarm of ants would readily overtop the wall). If the fence-webbing is loaded with some scent which ants find irritating, it would discourage any marauding ant from testing the fence.



Moths have also developed some elaborate defense systems (including fences) to protect pupating larvae from ants (and other similar-sized predators).



Urodus sp. [5]
Bucculatricidae [7]
Unidentified moth. [6]

Part 2