If you ask a group of friends what their biggest fear is, more than likely you’ll hear at least one person say “spiders”. The sight of just one spider will make them jump. How about thousands of spiders that appear to be raining down from the sky? This phenomenon of raining spiders was seen recently in Santo Antônio da Platina, Brazil. It was captured on video by a 20 year old graphic designer after leaving a friend’s party.
The type of spider witnessed in this video is called a Anelosimus eximius. It’s among a group of spiders that are considered to be social or communal spiders. Unlike other types of spiders, Anelosimus eximius work together to spin very large overlapping webs. They work together to take down prey that is much larger than themselves, which they share among all members of the group. Unlike non-social spiders, they take care of their young, and sometimes will take care of the young of other spiders who are in the group.
These spiders are more often found high in the canopy of a rainforest. Their massive webs catch anything that happens to pass through. The wind is stronger at these heights, so occasionally these tiny spiders, about the size of an ant, will be picked up by a strong gust of wind. For this reason, it might appear that the spiders are raining down. Their distribution is as far north as the Lesser Antilles, as far west as Panama and as far south as Argentina.
I’m sure the man who shot the video above has nothing to worry about, but that doesn’t mean that these little spiders aren’t a threat to smaller prey that lands in the web. While they are small, their cooperative nature and ferocity has been likened to a pack of lions. Watch this video as they attack and kill a much larger cricket.
The video above shows a colony in its natural habitat – a rainforest. It begs the question, why was the colony seen in the first video found in an urban setting strung between utility lines? While it’s not completely clear, there are several possibilities. One reason may be found in a study that showed that colonies located on the edges of the Amazon tended to have a much shorter lifespan. However, the concentration of colonies was higher on the exterior of the rainforest. While fewer trees is correlated with more colonies, the clear cutting and smoke associated with deforestation of the Amazon surely drives out many of the prey that would the spiders’ food source.
While climate change itself doesn’t seem to directly affect a colony as much as other insects, a colony is especially vulnerable to lack of genetic variation. One disadvantage of communal life is that there’s lots of interbreeding. If a parasite comes along, it can wipe out the whole colony in a short time. Could the group of spiders be adapting to its environment in the forest to the environment in the city?
While the level of deforestation has lessened a bit in the last few years, the overall loss of forest may explain the migration of these spiders from forested area to an urban area. It may also be a function of one predator leaving and another one moving in. When there’s a break in the food chain, one group dies out and another one takes over. One fact that is known about these spiders is that they do tend to congregate in places where other spiders used to be. While nothing is known for sure, it’s a possible explanation.
While I think these spiders are very interesting and amazing, there is probably a large group of you who are even more afraid of arachnids after seeing that helpless cricket. There’s no reason to fret. They’re probably more afraid of you, than you are of them, or are they? Mwhahaha!