It is raining spiders in Brazil.
February 9, 2013 12:20 PM   Subscribe

"Hundreds (maybe thousands) of spiders congregate between poles in the town of Santo Antonio de Plantina / PR."

According to G1 (Portugese), "A biologist who specializes in spiders of the Pontifical Catholic University of Paraná (PUC-PR), Marta Fischer, examined the picture and said that the phenomenon is normal and occurs mainly in the cities of São Paulo. "It is the kind of spider known as Anelosimus Eximius, which are social spiders. They are usually in trees during the day and in the late afternoon and early evening construct a sort of sheet webs, each makes his and then they come together. The goal is to capture insects," she explains, "During the day they destroy the webs to prevent birds do it," concludes Marta, who also said that the venom of this species causes no risks to humans."

These spiders work together to take down much larger prey than they could otherwise alone, as David Attenborough beautifully demonstrates on film
Benefits of cooperation with genetic kin in a subsocial spider
Interaction within groups exploiting a common resource may be prone to cheating by selfish actions that result in disadvantages for all members of the group, including the selfish individuals. Kin selection is one mechanism by which such dilemmas can be resolved This is because selfish acts toward relatives include the cost of lowering indirect fitness benefits that could otherwise be achieved through the propagation of shared genes. Kin selection theory has been proved to be of general importance for the origin of cooperative behaviors, but other driving forces, such as direct fitness benefits, can also promote helping behavior in many cooperatively breeding taxa. Investigating transitional systems is therefore particularly suitable for understanding the influence of kin selection on the initial spread of cooperative behaviors. Here we investigated the role of kinship in cooperative feeding. We used a cross-fostering design to control for genetic relatedness and group membership. Our study animal was the periodic social spider Stegodyphus lineatus, a transitional species that belongs to a genus containing both permanent social and periodic social species. In S. lineatus, the young cooperate in prey capture and feed communally. We provide clear experimental evidence for net benefits of cooperating with kin. Genetic relatedness within groups and not association with familiar individuals directly improved feeding efficiency and growth rates, demonstrating a positive effect of kin cooperation. Hence, in communally feeding spiders, nepotism favors group retention and reduces the conflict between selfish interests and the interests of the group.
More information on the spider:
Social spiders catch larger prey: a study of Anelosimus eximius (Araneae: Theridiidae)
During a 1-year-study in tropical Panama, prey of the social theridiid Anelosimus eximius was analysed at two locations and compared with the potential prey spectrum according to sweepnet catches, pitfall traps and bowl traps. Compared with other web-building spiders, A. eximius catch an unusually high number of large insects: about 90% are flying ants, beetles,lepidopterans hemipterans, cockroaches and grasshoppers. This is the result of a communal strategy to overwhelm prey. Webs are maintained commonly, and several spiders attack an entangled insect simultaneously. More spiders participate on insects that are larger and struggle more. The ability to catch large prey insects is discussed as a major driving factor for sociality in spiders.

Population genetics of Anelosimus eximius (Araneae, Theridiidae)
Anelosimus eximius is a cooperative, group-living neotropical spider. Colonies consist of up to several thousand individuals, and colonies may be aggregated into local colony clusters. The colony clusters are patchily distributed, and are often separated from their neighbors by a km or more. In this study individuals were collected from colonies located in Panama and Suriname. These individuals were subjected to horizontal starch gel electrophoresis and screened for polymorphisms in 46 enzyme systems. A total of 51 scorable loci were found, of which seven were polymorphic. The results were analyzed with Wright's F statistics which were used to investigate the amount of genetic differentiation in the population attributable to subdivision of the population into colonies, colony clusters, local populations and the geographic regions of Panama and Suriname. Most of the genetic differentiation in the A. eximius sampled was due to subdivision of the population into colony clusters and into geographic regions. There was no evidence of differentiation among colonies in a colony cluster, and little differentiation among collection sites within Panama or Suriname. In contrast, within a local population, samples from adjacent colony clusters were sometimes fixed for different alleles at one or more loci, and the Panama and Suriname samples were fixed for different alleles at three loci.
(The spider previously)
posted by Blasdelb (32 comments total) 32 users marked this as a favorite
This is so cool, Blasdelb! The video itself was really something to see, and I appreciated all the extra info you posted about their cooperative behaviour. Super neat (if a little freaky--I am not sure what my lizard brain would do if I saw that in real life).
posted by hurdy gurdy girl at 12:31 PM on February 9, 2013

The rise of Spider Communism is a historical inevitability
posted by The Whelk at 12:31 PM on February 9, 2013 [2 favorites]

Excellent post! Nightmarish subject, however :)
posted by sbutler at 12:33 PM on February 9, 2013

posted by rtha at 12:35 PM on February 9, 2013

This is incredibly fascinating, and very useful. Few posts give us so exactly the location where we do not want to be.

(Pro-spider, anti spiders falling on my head.)
posted by louche mustachio at 12:37 PM on February 9, 2013 [7 favorites]

Well, there is ONE spot I won't be travelling to.
posted by St. Alia of the Bunnies at 12:38 PM on February 9, 2013 [1 favorite]

Very cool. Giant floating spider invasion fleet.
posted by toadflax at 12:41 PM on February 9, 2013

I made Himself watch these too, so that later tonight when I wake up screaming he'll know why.
posted by Mary Ellen Carter at 12:43 PM on February 9, 2013 [1 favorite]

Wow, amazing! Relatedly.
posted by Westringia F. at 12:45 PM on February 9, 2013 [1 favorite]

I am thinking about 350KT will solve this problem.
posted by ROU_Xenophobe at 12:49 PM on February 9, 2013

posted by ramix at 12:54 PM on February 9, 2013

Echoing: Very cool, but NIMBY.
posted by maxwelton at 12:59 PM on February 9, 2013

*compulsively scratches scalp*
posted by TheWhiteSkull at 1:03 PM on February 9, 2013 [3 favorites]

I had suspicions Fritz Leiber faked his death and moved to South America. Only a matter of time before the Snakes show up.
posted by Smedleyman at 1:09 PM on February 9, 2013

Wow. I did really well until he zoomed in. And then it had to go.
posted by roomthreeseventeen at 1:13 PM on February 9, 2013

posted by Drexen at 2:01 PM on February 9, 2013 [1 favorite]

I actually witnessed it raining spiders in San Martin, California back when I was about ten years old.

It was during our recess on a somewhat blustery spring day. It was what I would describe as "kite flying weather", unsettled, with a lot of updraft and higher winds overhead. We were out playing and running around in a large grass field or near the school playground... and suddenly, you had visible spider threads everywhere, you were running into webs, and spiders flying through the sky everywhere. Some landed, most kind of seemed determined to bump into things, but keep flying wherever the wind would take them.

As you might expect, lots of the boys were fascinated, while several girls screamed and left the playground. I stayed in outside and got "spider whacked" once or twice, but only one landed on me, as far as I know. Most of them were pretty small, if I recall... but not tiny or unnoticeable. You could definitely see them flying through the air, on long webs.

I found out later that it's a phenomena known as ballooning, and not entirely uncommon. In fact, it's probably how islands like Hawaii got many of their spiders.
posted by markkraft at 2:31 PM on February 9, 2013 [1 favorite]

posted by Fists O'Fury at 3:02 PM on February 9, 2013

They're more afraid of you than you are of them.

No, I'm just kidding. You're much more afraid of them.
posted by not_on_display at 4:05 PM on February 9, 2013 [1 favorite]

I really like spiders, but this kind of creeped me out.
posted by mudpuppie at 4:23 PM on February 9, 2013

Shaky-cam footage, horrific creatures raining from the sky... J.J. Abrams must definitely be involved in this somehow.
posted by wolfdreams01 at 4:23 PM on February 9, 2013 [1 favorite]

Reminds me of this, but on a larger scale.
posted by SpacemanStix at 4:59 PM on February 9, 2013

Somebody posted this on the purple blobs in the desert thread from yesterday, and after the completely CGI UFO thread from earlier that day, I just assumed this was completely fake, like not just CGI spiders, but CGI everything.

Are you saying this is real? Because I was okay with it being CGI, but if this is real, I would like to unsee this please.
posted by etc. at 5:59 PM on February 9, 2013 [1 favorite]

jeebus fuck me running, my body just tried to turn itself inside-out to avoid any part of me touching a spider. I'm still kinda shaking. Don't these people have access to flamethrowers?
posted by Purposeful Grimace at 6:41 PM on February 9, 2013 [1 favorite]

posted by six-or-six-thirty at 7:04 PM on February 9, 2013 [4 favorites]

Wow, amazing! Relatedly.

Ha! Sorry, Westringia F. I missed that you had posted that already.
posted by SpacemanStix at 7:14 PM on February 9, 2013

I saw this video earlier, and I was quite sure that it was some sort of colonial spider, not a social spider, and definitely not Anelosimus. I have studied a related species, Anelosimus baeza, here in Mexico, and the webs are completely different. These spiders look like from a different family, though its really hard to tell with that ridiculously dizzy video. I would bet, that it's either Parawixia or Metepeira, but I haven't checked if Metepeira is found in Brazil.
posted by dhruva at 7:22 PM on February 9, 2013 [2 favorites]

Anelosimus eximius, on the other hand, are really cool. They also show this very weird sort of synchronization in movements, wherein they suddenly all stop moving at the same time, as if to listen to the prey without vibrational interference from other spiders.
posted by dhruva at 7:25 PM on February 9, 2013

Oh wow, I am in complete awe. This is equally fascinating and beautiful. I'd love to dream up a trip to witness this in person. Thank you for this fantastic post, Blasdelb.
posted by mayurasana at 8:48 PM on February 9, 2013

It's simple... some spiders lay their eggs in places where they're up high or otherwise unable to climb down, or simply find themselves overcrowded in a given area... and it behooves them to scatter themselves to the wind.

Having seen this before, I don't find it all that scary. This, however, is really messed up.
posted by markkraft at 10:26 PM on February 9, 2013



posted by lumpenprole at 1:21 AM on February 10, 2013

I am fascinated by spiders at a distance and totally creeped out in person. This posted video trips all my eeeeek-out wires.

I was similarly fascinated/creeped out by reading about the draping that spiders often do post-floods: See Pakistan and Wagga Wagga. The idea of surviving the horrors of a flood and then having to share my little survival patch of dry land with a teeming mass of millions of spiders is beyond horrific.

This is an interesting clip on ballooning spiders - how they move and spin.
posted by madamjujujive at 9:58 AM on February 10, 2013

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