WEBVTT - From the Vault: The Glorious Hermit Crab, Part 1 0:00:06.000 --> 0:00:08.600 Hey, welcome to Stuff to Blow your Mind. This is 0:00:08.680 --> 0:00:11.160 Robert Lamb. Today is Saturday, of course, so I have 0:00:11.240 --> 0:00:14.240 a vault episode for you. And oh, this one published 0:00:14.360 --> 0:00:17.800 a year ago this very day. This published on one 0:00:17.880 --> 0:00:21.280 four twenty four. It is part one in our series 0:00:21.320 --> 0:00:29.479 on the Hermit Crab. I hope you enjoy. 0:00:26.920 --> 0:00:30.760 Welcome to Stuff to Blow Your Mind, a production of iHeartRadio. 0:00:36.920 --> 0:00:39.160 Hey, welcome to Stuff to Blow your Mind. My name 0:00:39.200 --> 0:00:39.720 is Robert. 0:00:39.600 --> 0:00:42.680 Lamb and my name is Joe McCormick. And we're back 0:00:42.720 --> 0:00:45.680 after the holidays. All right, I guess you've already been back, Rob, 0:00:45.720 --> 0:00:47.000 I'm back for the first time. 0:00:46.840 --> 0:00:51.720 Now, Yeah, that's right. I left a little early and 0:00:51.840 --> 0:00:54.480 then and then I came back to you know, scrambled 0:00:54.520 --> 0:00:58.120 together a few episodes. But now it's time to return 0:00:58.280 --> 0:01:02.000 proper with a true core episode of Stuff Below Your Mind. 0:01:02.280 --> 0:01:05.200 But we're ringing in the new year once more with crabs, 0:01:05.240 --> 0:01:08.200 because of course, crab content is suitable for any holiday, 0:01:08.720 --> 0:01:11.200 and there is an abundance of it, you know. 0:01:11.280 --> 0:01:13.480 I don't know if it's just the name of Christmas 0:01:13.480 --> 0:01:16.960 Island that created this correlation, but I think we tend 0:01:16.959 --> 0:01:19.679 to do crab content in the winter have you noticed 0:01:19.720 --> 0:01:23.000 that that's not on purpose, at least not on my part. 0:01:23.000 --> 0:01:26.160 No, this is great. I think the Christmas Island crab 0:01:26.240 --> 0:01:29.760 thing kicked it off a bit a while back. That's 0:01:29.840 --> 0:01:34.000 part of it. For sure. There's something maybe holiday centric 0:01:34.000 --> 0:01:38.120 about crabs. It also helps that sometimes my family and 0:01:38.160 --> 0:01:41.399 I travel during the winter break and go somewhere where 0:01:41.480 --> 0:01:45.600 crabs are abundant. And yeah, I'm excited to talk about 0:01:45.640 --> 0:01:47.800 crabs once more because over the holidays, my family and 0:01:47.800 --> 0:01:51.200 I were fortunate enough to once more visit Glover's Reef, 0:01:51.560 --> 0:01:55.800 a partially submerged atoll located off the southern coast of Belize. 0:01:56.720 --> 0:01:59.040 Tremendous fun. We stayed on a small island all week. 0:01:59.120 --> 0:02:02.360 There were other human certainly, but we spend as much 0:02:02.360 --> 0:02:04.960 time as possible getting into the water to snorkel to 0:02:05.040 --> 0:02:07.559 check out the fish and the coral. But the predominant 0:02:07.640 --> 0:02:11.880 land organism was, without a doubt, the terrestrial hermit crab. 0:02:12.480 --> 0:02:14.520 So this is a holiday with crabs underfoot. 0:02:14.960 --> 0:02:17.560 Yes, I mean, I don't think anyone ever stepped on one, 0:02:17.600 --> 0:02:22.280 but they were everywhere. Most hermit crab species are aquatic, 0:02:22.320 --> 0:02:26.239 as we'll probably touch on several times during this episode. 0:02:27.120 --> 0:02:30.919 But I'm going to be talking mostly about the terrestrial variants, 0:02:30.720 --> 0:02:33.399 like those that I encountered on this island, that still 0:02:33.440 --> 0:02:36.200 depend on the ocean for reproduction, but which live most 0:02:36.240 --> 0:02:39.720 of their lives on land, and that comes with various 0:02:39.840 --> 0:02:45.080 complications and innovations. And also they're very visible. You know, 0:02:45.360 --> 0:02:47.560 you don't need a snorkel, you don't need a dive 0:02:47.639 --> 0:02:51.760 suit to engage with the world of the hermit crab 0:02:51.840 --> 0:02:54.280 because on places like this they are everywhere and they 0:02:54.280 --> 0:02:56.560 are widespread. You don't also don't have to go to 0:02:56.680 --> 0:03:00.680 Belize to encounter hermit crabs, terrestrial hermit crabs, even they 0:03:00.720 --> 0:03:01.320 are out there. 0:03:01.560 --> 0:03:04.400 So roughly, how big were or how big was the 0:03:04.520 --> 0:03:06.360 range of the ones you were seeing? Is are we 0:03:06.400 --> 0:03:10.960 talking like silver dollar size or hand size? Like what 0:03:11.000 --> 0:03:11.880 are we dealing with here? 0:03:12.320 --> 0:03:14.520 Yeah? The size differential is one of the things that 0:03:14.680 --> 0:03:17.680 makes hermit crab watching in the wild so fun because 0:03:17.880 --> 0:03:19.960 you never know exactly what size you're gonna encounter. Like 0:03:20.000 --> 0:03:22.400 some of the very small ones, you know, oh so cute, 0:03:22.440 --> 0:03:25.400 it's the size of a dime or something, you know, 0:03:25.400 --> 0:03:28.520 it's very small. But other times it'll be like I'm 0:03:28.520 --> 0:03:30.920 probably exaggerating to save the size of a catcher's met 0:03:32.080 --> 0:03:34.400 but at least the size of a very large fist, 0:03:34.480 --> 0:03:36.760 you know, just a just a big chonker of a 0:03:36.760 --> 0:03:39.880 hermit crab. And as you're going, as we were going 0:03:39.920 --> 0:03:43.520 about on the little pathways on the island, you know, 0:03:43.640 --> 0:03:45.920 they would be moving around pretty much all the time. 0:03:46.800 --> 0:03:50.880 That they're very busy. They're constantly trooping about, they're scavenging, 0:03:51.200 --> 0:03:53.440 they're competing for shells. Though I don't think we ever 0:03:53.760 --> 0:03:57.560 directly observed this, but clearly it is happening. And if 0:03:57.560 --> 0:04:00.600 you come across one while it's say, crossing the sand path, 0:04:01.440 --> 0:04:03.640 they'll suddenly stop, and then if you get a little 0:04:03.640 --> 0:04:06.240 bit closer, they'll retreat into their shells, and as they 0:04:06.240 --> 0:04:08.400 do that, that'll cause them to roll over onto their back, 0:04:08.680 --> 0:04:11.080 and then of course they cap the shell opening with 0:04:11.280 --> 0:04:13.840 their larger claw and then give them enough time and 0:04:13.880 --> 0:04:15.880 then get back up and they continue on with their business. 0:04:16.040 --> 0:04:16.440 Mm hmm. 0:04:17.560 --> 0:04:20.760 So yeah, there's just something magical about her crabs, at 0:04:20.839 --> 0:04:22.640 least to someone like me who doesn't get to observe 0:04:22.680 --> 0:04:25.000 them all the time. But even the team on the 0:04:25.000 --> 0:04:26.800 island here, they seem to find a certain amount of 0:04:26.880 --> 0:04:29.800 joy in the creatures, despite how accustomed they were to 0:04:29.839 --> 0:04:33.120 their presence. I heard that one of the cooks brought 0:04:33.760 --> 0:04:38.599 some shells for the crabs with her from the mainland, 0:04:38.160 --> 0:04:41.039 with the names of each of her children written on them, 0:04:41.480 --> 0:04:44.880 and then and then would enjoy like running into various 0:04:44.880 --> 0:04:48.039 crabs who would claim these shells and make them their homes. 0:04:48.320 --> 0:04:51.200 Oh, that's funny. So like when people write funny things 0:04:51.200 --> 0:04:53.680 on a dollar, you know, it's like, are you expecting 0:04:53.720 --> 0:04:54.799 to encounter this again? 0:04:55.600 --> 0:04:58.520 Yeah? Yeah, And yeah. There's just something they're like a 0:04:58.520 --> 0:05:02.680 little like io machines, you know. There's just something about 0:05:03.120 --> 0:05:06.640 how industrious and relentless they are as they scavenge the terrain. 0:05:07.360 --> 0:05:10.359 For instance, at this place that we were staying, this 0:05:10.400 --> 0:05:13.360 a place called Off the Wall. The communal dining area 0:05:13.440 --> 0:05:17.440 at the place has a sand floor, and Jim and Kindre, 0:05:17.480 --> 0:05:19.200 who run the place, told us that first thing in 0:05:19.200 --> 0:05:21.640 the morning, when you go in there, the sand is 0:05:21.680 --> 0:05:25.520 completely devoid of human footprints because during the night the 0:05:25.560 --> 0:05:28.320 crabs have come, the hermit crabs have come, and so 0:05:28.600 --> 0:05:31.280 in the morning they are only crab tracks, and not 0:05:31.960 --> 0:05:34.800 even the slightest crumb left behind, because they have come 0:05:34.839 --> 0:05:35.840 and claimed everything. 0:05:36.320 --> 0:05:37.120 Crab wipe. 0:05:37.520 --> 0:05:41.640 Yeah, so I love it. After experiencing all that, I 0:05:41.680 --> 0:05:43.240 was like, well, we've got to find some more things 0:05:43.240 --> 0:05:45.680 to talk about with hermit crabs. We've talked about them before, 0:05:46.200 --> 0:05:47.839 but now we're going to go in a little more depth. 0:05:48.080 --> 0:05:51.200 Well, it turns out I think hermit crabs are very 0:05:51.200 --> 0:05:54.080 interesting and there is a lot we can talk about. 0:05:54.160 --> 0:05:57.120 So I guess we will start with the basics. What 0:05:57.279 --> 0:06:01.279 are hermit crabs? Are hermit crabs crab? The answer is 0:06:01.760 --> 0:06:06.839 sort of. Hermit crabs are decapod crustaceans that means decapod. 0:06:06.839 --> 0:06:11.839 They're ten legged invertebrates with a hard exoskeleton that grow 0:06:11.960 --> 0:06:15.680 by molting, so they shed their old exoskeleton and emerge soft, 0:06:15.720 --> 0:06:18.160 and then a new exoskeleton hardens when they need to 0:06:18.160 --> 0:06:21.440 get bigger when they grow bigger. But they are considered 0:06:21.480 --> 0:06:25.320 distinct from what are called true crabs. True crabs belong 0:06:25.400 --> 0:06:30.120 to the infraorder Brachyuria. Hermit crabs belong to the related 0:06:30.200 --> 0:06:34.320 infraorder animura a n O m U r A. They're 0:06:34.480 --> 0:06:38.720 close cousins to true crabs, but different. Other animurins or 0:06:38.760 --> 0:06:43.360 false crabs include the lithodoidea or the king crabs. And 0:06:43.440 --> 0:06:47.880 the Porcelinidae, which are the porcelain crabs. And one thing 0:06:47.960 --> 0:06:52.560 animurins generally have in common is that. Okay, so these 0:06:52.640 --> 0:06:55.800 decapods all have five pairs of legs ten legs total, 0:06:56.279 --> 0:06:59.640 and in the animurans, the last pair of legs farthest 0:06:59.640 --> 0:07:03.680 away from the head is fun sized. So these animals 0:07:03.720 --> 0:07:06.880 are still decapods, but a lot of them look like 0:07:06.960 --> 0:07:09.840 they have only eight legs instead of ten, or maybe 0:07:09.920 --> 0:07:14.000 six legs and two claws. Those front legs, the chelli 0:07:14.160 --> 0:07:17.040 or the claws are legs, but in crabs they're often 0:07:17.240 --> 0:07:20.160 claw shaped, but they look like they have only eight 0:07:20.480 --> 0:07:24.600 legs instead of ten because the hindmost pair is tiny 0:07:24.640 --> 0:07:27.600 and often hidden or tucked away under another body part. 0:07:28.000 --> 0:07:31.600 Yeah, and we'll get back to this particular detail later 0:07:31.640 --> 0:07:34.000 on in our discussion. If not this episode, then perhaps 0:07:34.080 --> 0:07:35.200 the second episode. 0:07:35.440 --> 0:07:38.240 So animurans have ten legs, a lot of times it 0:07:38.240 --> 0:07:39.160 looks like they only have. 0:07:39.240 --> 0:07:39.440 Eight. 0:07:40.240 --> 0:07:45.600 Hermit crabs belong in the taxonomic superfamily Pagurroidea, and with 0:07:45.800 --> 0:07:50.000 a few exceptions, they are mostly notable for exactly what 0:07:50.040 --> 0:07:55.000 you're thinking of their dependence on externally scavenged material for 0:07:55.280 --> 0:07:59.760 armor and shelter. Usually this armor is a shell that 0:08:00.080 --> 0:08:04.640 once belonged to a gastropod, such as a snail, a periwinkle, 0:08:04.840 --> 0:08:07.800 or a whelk, though there are some animals in the 0:08:07.840 --> 0:08:10.960 family that don't need scavin shelter at all. We can 0:08:11.000 --> 0:08:12.960 talk about those in a minute, and there are a 0:08:12.960 --> 0:08:16.720 few that rely on things other than mollusk shells. One 0:08:16.760 --> 0:08:18.720 example cited in a paper that I'll get to in 0:08:18.760 --> 0:08:24.000 a minute is the discorso Pagurus schmitti, which takes up 0:08:24.000 --> 0:08:27.600 shelter not in a gastropod shell, but in empty polyheat 0:08:27.680 --> 0:08:32.680 worm tubes. The hermit crabs that do rely on external 0:08:32.720 --> 0:08:37.280 mollusk shells have bodies that are actually shaped by this need. 0:08:37.840 --> 0:08:42.520 So while true crabs have hard exoskeletons covering their entire bodies, 0:08:42.960 --> 0:08:48.080 hermit crabs have what you might call non calcified abdomens. 0:08:48.440 --> 0:08:51.200 So the front facing part of a hermit crab's body 0:08:51.240 --> 0:08:54.240 the head, the thorax, and the front pairs of legs 0:08:54.240 --> 0:08:58.400 and claws. These all have hard exoskeletal coating like any 0:08:58.440 --> 0:09:01.760 other crab, but the part of the hermit crab the 0:09:01.800 --> 0:09:04.880 abdomen in what you might call the tail or the Telson. 0:09:05.920 --> 0:09:09.600 This doesn't really resemble a crab body at all in 0:09:09.679 --> 0:09:11.400 a lot of species. It looks kind of like a 0:09:11.520 --> 0:09:16.000 curly fat worm, and it does not have a hard exoskeleton. 0:09:16.360 --> 0:09:20.920 The abdomen is flexible, soft and vulnerable. It is covered 0:09:20.960 --> 0:09:24.960 in an external coating, but it's just very thin and soft. 0:09:25.040 --> 0:09:28.680 It's very uncrab. This is the part of a hermit 0:09:28.720 --> 0:09:32.800 crab that curls up inside the externally sourced shell. 0:09:33.440 --> 0:09:36.199 Yeah, so if you're just encountering hermit crabs out in 0:09:36.240 --> 0:09:39.880 the wild, or even seeing them in a an enclosure somewhere, 0:09:40.480 --> 0:09:43.080 you're probably not going to see this part of the 0:09:43.240 --> 0:09:48.360 organism with its abdomen inside the shell. As we've been discussing, 0:09:48.400 --> 0:09:50.760 it actually walks on its second or in third pairs 0:09:50.800 --> 0:09:54.120 of legs. The first pairs are modified to form pinchers, 0:09:54.640 --> 0:09:57.040 and its fourth and fifth pairs of legs are small 0:09:57.080 --> 0:10:00.840 and specialized to grip the inside of the shell. It 0:10:00.880 --> 0:10:03.719 also has appendages called europods at the end of its 0:10:03.720 --> 0:10:06.440 abdomen to aid and securing that shell. So, you know, 0:10:06.840 --> 0:10:09.439 all these things aiding to sort of grip and hold 0:10:09.480 --> 0:10:12.640 on to that shell that it has taken on as 0:10:12.679 --> 0:10:17.800 its shelter. The larger left europod hooks the central post 0:10:17.960 --> 0:10:20.559 of a shell, and they can also use this europod 0:10:20.600 --> 0:10:22.800 to hold on to other things when they are out 0:10:22.840 --> 0:10:25.520 of the shell, Like I've read about how they can 0:10:25.640 --> 0:10:27.839 attach to say like a tree or something, and it 0:10:27.880 --> 0:10:29.720 can also use it to maintain balance. 0:10:30.559 --> 0:10:33.199 Yeah, so I think it's interesting that the hermit crab 0:10:33.320 --> 0:10:37.760 is an animal. Its body is shaped in for double purpose. 0:10:38.280 --> 0:10:41.800 So the front end of it is shaped for facing 0:10:41.880 --> 0:10:44.440 the external world. It has the chelly, it has the 0:10:44.520 --> 0:10:47.800 claws like many other crabs you would think of, but 0:10:47.840 --> 0:10:50.800 the back end of it is shaped entirely for holding 0:10:50.960 --> 0:10:55.000 on to this piece of mobile shelter. And the concept 0:10:55.120 --> 0:10:59.960 of mobile shelter, while not completely unique, is pretty unique. 0:11:00.000 --> 0:11:03.000 What makes the hermit crab interesting To read a quote 0:11:03.040 --> 0:11:06.360 from a highly cited paper on hermit crabs that I 0:11:06.400 --> 0:11:10.040 was looking at by a biologist named Brian Hazlet. The 0:11:10.080 --> 0:11:14.480 paper is called the Behavioral Ecology of Hermit Crabs. Haslet writes, quote, 0:11:14.559 --> 0:11:19.360 Many animals utilize exogenous shelters, but almost all eight hundred 0:11:19.400 --> 0:11:24.600 species of hermit crabs are mobile while sheltered, the combination 0:11:24.720 --> 0:11:29.520 of mobility and protection afforded by this lifestyle must contribute 0:11:29.559 --> 0:11:32.720 to the large numbers of these crustaceans found in virtually 0:11:32.880 --> 0:11:37.360 all marine environments as well as in tropical terrestrial shores. 0:11:38.280 --> 0:11:42.680 So Hazlit is sort of saying the hermit crab plan 0:11:43.080 --> 0:11:46.920 is a successful plan, clearly shown by the diversity of 0:11:46.960 --> 0:11:50.200 these species found all around the world. That this is 0:11:50.240 --> 0:11:54.560 a plan that works because sourcing shelter from outside the 0:11:54.600 --> 0:11:57.600 body that you can take with you when you move 0:11:58.160 --> 0:12:02.480 works really well. But it also comes with costs, and 0:12:02.520 --> 0:12:05.920 we'll talk about those costs as we go on. One 0:12:05.960 --> 0:12:09.520 thing I think to understand is that in general, while 0:12:09.600 --> 0:12:13.760 a hermit crab can leave its externally acquired shell and 0:12:13.800 --> 0:12:17.920 it can survive for some time outside of its external shell, 0:12:18.520 --> 0:12:21.560 the acquisition of a shell for external armor is not 0:12:22.080 --> 0:12:24.680 optional for a hermit crab. It's not like a nice 0:12:24.720 --> 0:12:28.720 to have. It is essential for survival in the wild, 0:12:29.080 --> 0:12:31.960 and the hermit crab's evolution has been shaped by the 0:12:32.080 --> 0:12:34.960 need for these externally sourced shells. 0:12:35.720 --> 0:12:38.280 Yeah. Yeah, this is not just somewhere it goes to 0:12:38.320 --> 0:12:40.400 sleep at night like. It has to have this with it, 0:12:40.480 --> 0:12:42.640 and if it does not have the shell, then it 0:12:42.679 --> 0:12:47.320 is highly vulnerable to predation. Exposure. It very well likely 0:12:47.360 --> 0:12:48.600 will not survive without it. 0:12:48.920 --> 0:12:52.120 Right, So I want to turn to a paper I 0:12:52.160 --> 0:12:55.360 was reading for a general overview of hermit crabs and 0:12:55.400 --> 0:12:58.920 related species. This was an overview published in the journal 0:12:58.960 --> 0:13:03.000 Current Biology called the Hermit Crabs by Mark Brifa and 0:13:03.200 --> 0:13:06.800 Sophie L. Moles in two thousand and eight. And they're 0:13:06.840 --> 0:13:08.200 going to pat the picture here of the kind of 0:13:08.240 --> 0:13:12.680 hermit crab family tree. So there are currently more than 0:13:12.760 --> 0:13:16.720 eight hundred known species of hermit crabs. Most of these 0:13:16.760 --> 0:13:20.640 species live in the ocean their marine, with a few exceptions. 0:13:20.920 --> 0:13:25.840 One is a species called Clibinarius fontic cola, and this 0:13:26.000 --> 0:13:31.640 is the only known freshwater hermit crab which lives in Vanuatu, 0:13:31.760 --> 0:13:35.959 that's a volcanic archipelago in the Pacific. And there are 0:13:36.080 --> 0:13:39.480 other freshwater and amurans, but they are not hermit crabs. 0:13:40.000 --> 0:13:43.240 So this is the one freshwater hermit crab out there. 0:13:43.600 --> 0:13:45.880 I should throw in that the hermit crabs that we 0:13:45.880 --> 0:13:48.360 were observing in the wild, I believe are the Caribbean 0:13:48.400 --> 0:13:53.240 hermit crab, and this is a variety that's common to 0:13:53.679 --> 0:13:57.439 the West Atlantic, Belize, Southern Florida, Venezuela, and the West Indies. 0:13:57.679 --> 0:13:59.480 Yes, and the ones you were observing you were saying 0:13:59.679 --> 0:14:02.719 were terrestrial or semi terrestrial, right, they spend a lot 0:14:02.720 --> 0:14:03.520 of time on land. 0:14:03.800 --> 0:14:06.679 Yeah, these were land boys. We did see one variety 0:14:06.760 --> 0:14:09.959 and I didn't identify this one one variety of aquatic 0:14:09.960 --> 0:14:13.400 hermit crab out law snorkeling. But yes, the ones that 0:14:13.440 --> 0:14:17.600 I'm mostly talking about here are hermit crabs of terrestrial 0:14:17.640 --> 0:14:18.320 hermit crabs. 0:14:18.720 --> 0:14:22.200 So there are about a dozen species of land dwelling 0:14:22.280 --> 0:14:25.800 or semi land dwelling hermit crab descendants in a family 0:14:25.880 --> 0:14:31.280 called Sinobotids. This family includes one famous species that has 0:14:31.400 --> 0:14:35.080 shed its need for an externally acquired shell altogether, and 0:14:35.120 --> 0:14:38.760 that is the coconut crab or robber crab. We've talked 0:14:38.840 --> 0:14:41.680 extensively about these before, but the coconut crab is the 0:14:41.840 --> 0:14:45.920 largest land dwelling invertebrate in the world. I can have 0:14:45.960 --> 0:14:48.120 a leg span of up to one meter and can 0:14:48.160 --> 0:14:51.600 weigh almost five kilograms or about ten pounds. They live 0:14:51.680 --> 0:14:55.160 mostly in coastal areas throughout the Indian and Pacific oceans. 0:14:56.000 --> 0:14:58.680 I think we talked a good bit about coconut crabs 0:14:58.680 --> 0:15:01.040 in our series on the Christmas Island crabs that we 0:15:01.080 --> 0:15:04.240 did several years back. This was the the animal where 0:15:04.480 --> 0:15:06.760 we were talking about the field notes of Darwin from 0:15:06.800 --> 0:15:08.880 the Voyage of the Beagle, where he's like, you know, 0:15:08.920 --> 0:15:12.120 they make really good eat and you boil the fat 0:15:12.200 --> 0:15:14.760 under their tail and it makes a quart bottle of 0:15:14.800 --> 0:15:17.680 limpid oil. And then he also tells a story about 0:15:17.720 --> 0:15:20.920 how they like locked one inside of a biscuit tin 0:15:21.120 --> 0:15:24.120 with wire and using its claws it was able to 0:15:24.320 --> 0:15:27.360 essentially like rip the tin out and escape the box. 0:15:28.000 --> 0:15:31.280 Oh man, there's a whole horror movie for you right there. Yeah, 0:15:31.360 --> 0:15:34.680 it would be Charles Darwin and crew on the Beagle 0:15:34.760 --> 0:15:36.960 having to fight off the killer coconut crab. 0:15:37.320 --> 0:15:39.520 They come and they just find the empty box. They're like, 0:15:39.560 --> 0:15:45.120 it's loose. No one knows where, you know, as long 0:15:45.160 --> 0:15:46.040 as we're throwing around. 0:15:46.320 --> 0:15:49.880 Charles Darwin quotes there's another place in the Voyage of 0:15:49.920 --> 0:15:53.880 the Beagle where he mentions hermit crabs. This is not 0:15:54.000 --> 0:15:57.360 a particularly insightful quote. It's just a mention, but I 0:15:57.400 --> 0:16:00.000 still had to drag it out. Quote. In every part 0:16:00.080 --> 0:16:03.160 art one meets hermit crabs of more than one species, 0:16:03.440 --> 0:16:06.160 carrying on their backs the shells which they have stolen 0:16:06.400 --> 0:16:10.120 from the neighboring beach stolen. And yes, there is a 0:16:10.160 --> 0:16:14.480 fair amount of shell theft as we'll get into. As 0:16:14.480 --> 0:16:17.440 long as you're thrown around quotes unrelated, I want to 0:16:17.520 --> 0:16:20.400 throw in this quote from Aristotle from the History of Animals. 0:16:20.600 --> 0:16:22.040 Is he going to tell us where they come from? 0:16:22.480 --> 0:16:25.800 Yes? Yes, you will reveal the at the time, you know. 0:16:25.960 --> 0:16:31.240 Non controversial hypothesis on crab origins quote. The hermit crab 0:16:31.280 --> 0:16:35.000 grows spontaneously out of soil and slime and finds its 0:16:35.000 --> 0:16:39.320 way into untenanted shells. As it grows, it shifts to 0:16:39.360 --> 0:16:42.400 a larger shell, as for instance, into the shell of 0:16:42.440 --> 0:16:46.640 the neartes, or of the strombus or the like, and 0:16:46.760 --> 0:16:50.160 very often into the shell of the small cirrix. After 0:16:50.320 --> 0:16:52.920 entering a new shell, it carries it about and begins 0:16:52.960 --> 0:16:55.560 again to feed, and by and by, as it grows 0:16:55.600 --> 0:16:58.240 it shifts again into another larger one. 0:16:58.920 --> 0:17:03.520 Okay, I give Aristotle half credit on this. I think 0:17:03.520 --> 0:17:06.320 he's a bit wrong on the spontaneous generation out of 0:17:06.359 --> 0:17:10.760 slime and soil, but he correctly observes the shell shifting 0:17:11.000 --> 0:17:15.040 behavior of hermit crabs, which is a major feature of 0:17:15.080 --> 0:17:17.720 hermit crabs society that we'll have to talk about later 0:17:17.760 --> 0:17:18.480 in the episode. 0:17:19.000 --> 0:17:23.119 Yeah, he's absolutely wrong on spontaneous generation. We don't ever 0:17:23.119 --> 0:17:25.840 really have to drive that home. But in a weird way, 0:17:26.320 --> 0:17:29.040 like in a very general way, the idea of like 0:17:29.840 --> 0:17:34.560 matter becomes crabs, nature becomes crabs. Maybe not that far off, 0:17:34.640 --> 0:17:35.760 as we'll discuss later on. 0:17:36.480 --> 0:17:39.880 But apart from the coconut crab, there are various other 0:17:39.920 --> 0:17:43.600 species of hermit crab that live basically would live their 0:17:43.640 --> 0:17:46.720 adult lives on land, though they still usually live out 0:17:46.800 --> 0:17:49.680 part of their life cycle in the water, with females 0:17:49.760 --> 0:17:54.160 releasing larvae into the sea, and apart from these exceptions, 0:17:54.160 --> 0:17:56.240 hermit crabs are marine species. 0:17:56.520 --> 0:17:58.679 Absolutely. We'll come back to some of the ramifications of 0:17:58.720 --> 0:18:09.800 this in a bit now. 0:18:09.800 --> 0:18:13.119 According to Brifa and Moles, there are five families of 0:18:13.119 --> 0:18:16.560 hermit crabs, and it breaks down like this. You've got pagurity, 0:18:16.680 --> 0:18:20.879 which are the right handed hermit crabs, and you've got diogeneity, 0:18:21.080 --> 0:18:25.359 which are the left handed hermit crabs right handed, left handed, 0:18:25.400 --> 0:18:27.879 What does that mean? We'll come back to that. Then 0:18:27.920 --> 0:18:31.640 you've got cenobitity, which are the land hermit crabs. You've 0:18:31.680 --> 0:18:35.639 got parapagurity, which are the deep sea hermit crabs, and 0:18:35.680 --> 0:18:40.439 you've got pilochelady, which are symmetrical hermit crabs. Though the 0:18:40.640 --> 0:18:43.960 more than eight hundred species of hermit crabs display different 0:18:44.160 --> 0:18:48.600 local adaptations and behaviors, for the most part, it seems 0:18:48.640 --> 0:18:53.040 like hermit crabs take what you can get foragers, which 0:18:53.160 --> 0:18:57.240 is true of many true crabs as well, But hermit crabs, 0:18:57.280 --> 0:19:00.000 for the most part, they will eat bits of dead 0:19:00.080 --> 0:19:03.280 organic matter, both animal and vegetable. They will eat live 0:19:03.400 --> 0:19:06.440 prey when they can catch it. Like true crabs, most 0:19:06.440 --> 0:19:10.000 hermit crabs are not very picky about food. Whatever they 0:19:10.000 --> 0:19:11.880 can get in their mouth, they're probably gonna eat. 0:19:12.920 --> 0:19:15.679 Yeah. Yeah. Both times that I was in believes there 0:19:15.720 --> 0:19:17.159 was a lot of fun to be had, especially with 0:19:17.240 --> 0:19:20.640 the kids, of leaving something out for them with permission 0:19:20.640 --> 0:19:23.359 of course, like I'm talking about the like like a 0:19:23.400 --> 0:19:28.080 cracked coconut, and then seeing the hermit crabs eventually swarm 0:19:28.200 --> 0:19:29.000 over the material. 0:19:30.560 --> 0:19:33.960 So while foraging for food is of course essential for survival, 0:19:34.080 --> 0:19:38.359 so is foraging for shelter. We will have more to 0:19:38.359 --> 0:19:40.199 say about this as we go on, but obviously a 0:19:40.320 --> 0:19:45.000 huge part of the hermit crab's survival revolves around acquiring 0:19:45.080 --> 0:19:48.000 a good shell to live in, and the majority of 0:19:48.040 --> 0:19:51.680 these shells come from As we've said, mollusks like snails, 0:19:52.040 --> 0:19:55.960 but hermit crabs don't have to fight the snail for 0:19:56.119 --> 0:19:59.439 its shell. They generally move into the shell that is 0:19:59.520 --> 0:20:04.159 left behind behind after a snail dies. Also, finding a 0:20:04.200 --> 0:20:07.840 shell is not a one time pursuit. Hermit crabs grow 0:20:07.960 --> 0:20:11.040 larger throughout their lives, which means they need to trade 0:20:11.160 --> 0:20:14.400 up for bigger shells, which can lead to very interesting 0:20:14.480 --> 0:20:18.320 mass behaviors. More on that later. One thing the authors 0:20:18.359 --> 0:20:21.760 of this overview point out is that the gastropod shell 0:20:21.920 --> 0:20:25.160 filled by a hermit crab is not only a hard 0:20:25.200 --> 0:20:27.919 surface to protect the soft part of the body, the 0:20:27.960 --> 0:20:31.400 soft abdomen, it also forms a kind of shelter against 0:20:31.400 --> 0:20:35.119 the external environment. Now what kind of shelter against the 0:20:35.200 --> 0:20:38.280 environment would a hermit crab need. One example I recall 0:20:38.320 --> 0:20:41.919 from some documentary footage I saw years ago, was the 0:20:41.920 --> 0:20:45.119 idea that a hermit crab that's on land is under 0:20:45.119 --> 0:20:48.479 the hot sun, and if it's got soft body parts 0:20:48.520 --> 0:20:51.000 exposed outside of the shell, it could quickly sort of 0:20:51.040 --> 0:20:54.440 bake and dry out without the shelter and moisture provided 0:20:54.480 --> 0:20:55.000 by a shell. 0:20:55.760 --> 0:20:58.320 Yeah, absolutely, Yeah. There again, we have to keep in 0:20:58.359 --> 0:21:02.200 mind that even they are terrestrial, they are linked inherently 0:21:02.240 --> 0:21:05.920 to the ocean, and especially when you're dealing with tropical 0:21:05.960 --> 0:21:09.040 heat environments. Yeah, they've they have to use that shell 0:21:09.080 --> 0:21:11.560 also to protect themselves and carry around some moisture. 0:21:11.840 --> 0:21:13.840 So I think it makes sense to look at a 0:21:13.880 --> 0:21:17.879 hermit crab's external shell in two different ways that both 0:21:17.960 --> 0:21:21.280 have some truth to them. On one hand, you could 0:21:21.280 --> 0:21:25.960 look at the external shell as an outsourced exoskeleton. It is, 0:21:26.160 --> 0:21:28.680 you know, it's like doing the role that would normally 0:21:28.760 --> 0:21:33.480 be done by the hard kiteness outer skeleton of a 0:21:33.520 --> 0:21:36.280 true crab. But another way to think of it is 0:21:36.320 --> 0:21:39.200 that it's like a portable burrow. And this is the 0:21:39.240 --> 0:21:41.760 point that Brian Haslitt was making in that quote I 0:21:41.800 --> 0:21:45.080 read earlier about the idea of mobile shelter. Lots of 0:21:45.160 --> 0:21:48.400 animals find holes to hide in, and rocks or other 0:21:48.480 --> 0:21:52.440 objects with recesses to provide a protective home. Hermit crabs 0:21:52.560 --> 0:21:57.720 find protective recesses that can actually come along anywhere with them. Now, 0:21:57.760 --> 0:22:00.560 I wanted to come back to the concept of ace symmetry, 0:22:00.560 --> 0:22:03.840 which we already mentioned Rob, you brought it up earlier, 0:22:03.880 --> 0:22:06.520 and it came up in the idea that there are 0:22:06.560 --> 0:22:11.000 these different families of hermit crabs, the right handed hermit crabs, 0:22:11.040 --> 0:22:15.280 the pagurady and the left handed hermit crabs. The diogeneity. 0:22:15.760 --> 0:22:18.960 Yeah, this is all very important because we think about 0:22:18.960 --> 0:22:22.840 the asymmetry of the crab in this case, and this 0:22:23.520 --> 0:22:26.360 lines up with the asymmetry of the shells that they 0:22:26.359 --> 0:22:27.600 are probably going to be inhabiting. 0:22:28.040 --> 0:22:31.119 Right, So, one thing is that hermit crabs have a 0:22:31.160 --> 0:22:34.520 directional curve in the abdomen. The abdomen can kind of 0:22:35.480 --> 0:22:39.040 curl in a spiraling direction one way or the other. 0:22:39.400 --> 0:22:41.800 But there's also an important difference in the size of 0:22:41.840 --> 0:22:44.679 the claws. And from what I could tell, it was 0:22:44.720 --> 0:22:47.760 the claw asymmetry that was primarily used to sort these 0:22:47.800 --> 0:22:52.080 animals into the different families. One claw is often bigger 0:22:52.119 --> 0:22:55.119