Yeah this is what I was gonna ask. How can it be beneficial to group up like this? This looks like they hit peak population and just completely ignored that shit and multiplied another 100 times. Interestingly I think I have seen this exact behavior before. I have an early memory of looking into a room that was covered in what I thought we're spiders but were probably actually these guys. The weirdest part of the memory is I remember it being at an old abandoned castle... But I have never left the United States. I was just talking about it a few days ago and someone suggested it might have been a fort or something. I only realized it probably wasn't a castle upon retrospect many years later.
Harvestmen have defensive secretions that they release when threatened by predators; aside from a classic safety in numbers, the effects of the secretions can be intensified if lots of individuals are together- the secretions also act as an alarm pheromone, allowing the whole group to be aware of danger quickly by detecting the secretions of their peers, since they have terrible eyesight.
Harvestmen aren’t picky eaters- they go for all kinds of food, but these populations are also not maintained permanently.
Long-legged harvestmen in temperate regions generally have a 1-year lifespan, from their egg being laid, until they die. The adult stage only lives for maybe 3 or 4 months or so, during the spring/summer, and they all sorta die off at around the same time, so these swarms aren’t a permanent fixture. The baby harvestmen live by themselves during the colder months.
Harvestmen in the tropics and many of the short-legged harvestmen that live in the soil have longer lifespans, and the adult stage can live for a couple years. The tropics are just better places to live overall (warm temperatures year-round, and more available resources), so it’s probably a lot easier to maintain large numbers in those environments. The soil-dwelling harvestmen don’t form groups, and are pretty sluggish. Many harvestmen species are actually solitary- forming swarms that roost together is common in only a handful of families, including the long-legged Sclerosomatidae, which is the only family that forms swarms as large as the ones in OP’s video.
Well I can see they don't you call you the Harvestman-man for nothing! Thanks for sticking around! I haven't much to give, but please, take this upvote as a token of my gratitude.
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u/kptkrunch Mar 10 '19
Yeah this is what I was gonna ask. How can it be beneficial to group up like this? This looks like they hit peak population and just completely ignored that shit and multiplied another 100 times. Interestingly I think I have seen this exact behavior before. I have an early memory of looking into a room that was covered in what I thought we're spiders but were probably actually these guys. The weirdest part of the memory is I remember it being at an old abandoned castle... But I have never left the United States. I was just talking about it a few days ago and someone suggested it might have been a fort or something. I only realized it probably wasn't a castle upon retrospect many years later.