Sloth crosses road: insert joke here

The poor beast can’t help it: the species evolved before there were roads!

The video describes this as “a sloth attempting to cross a busy road in Manuel Antonio, Costa Rica.”  This looks to me like the brown-throated sloth (Bradypus variegatus), of which I saw many during a summer in Costa Rica. Note the algae growing in its fur; one sloth expert describes its biological significance:

What I find most interesting about the three-toed sloth is the symbiotic relationship it has with other organisms. One effect of the sloth’s languid pace of life is that it can’t be bothered to groom itself. This turns out to be beneficial to several varieties of algae and mold that grow inside the sloth’s hollow hairs. The algae effectively turn the sloth green, giving it excellent camouflage among the leaves. The camouflage is crucial to the sloth’s survival, because its inability to move quickly makes it an easy target for the harpy eagle.

But the symbiosis doesn’t end there. The algae in the sloth’s fur provides food for a great many insects. (I should point out, incidentally, that sloths have extremely long fur, making them appear much larger than they really are.) Beetles have been found by the hundreds living on a single sloth. Another insect that calls the sloth home is a type of moth—Bradipodicola hahneli (or “sloth moth” to most people). The sloth’s fur provides both food and protection for the moth. Not only does it feed on the algae, but it also deposits its eggs in the sloth’s droppings, where they pupate and hatch, and then fly off to look for another sloth to live on.

h/t: Matthew Cobb


  1. Damnyankees
    Posted May 18, 2011 at 2:05 pm | Permalink

    I don’t know why, but I felt bad for the sloth. There’s no logical reason I should, any more than I would feel bad for a video of a human trying to climb a tree.

    • TrineBM
      Posted May 18, 2011 at 2:27 pm | Permalink

      I felt awful, because I couldn’t help laughing. Poor thing, though.

    • Dominic
      Posted May 18, 2011 at 2:43 pm | Permalink

      It is a remarkable creature with the huge fore limbs & tiny rear legs! The guy who picks it up has clearly done so before as he seems wary of the claws. I am curious – are they always so easy to catch? Do they taste bad & is that why they have not been wiped out?

      • Posted May 18, 2011 at 2:53 pm | Permalink

        I think they are damn near invisible when in the trees, where they spend most of their lives.

      • Posted May 18, 2011 at 3:25 pm | Permalink

        Do they taste bad…?

        Sinfully good. But deadly.


        • Dominic
          Posted May 19, 2011 at 1:53 am | Permalink

          🙂 very good!

  2. Posted May 18, 2011 at 2:29 pm | Permalink

    Oh boy, the “gringos” at the end are the cherry on top!

  3. Diane G.
    Posted May 18, 2011 at 2:45 pm | Permalink

    Watching sloths on the ground always gives me a squicky feeling–something too humanoid-looking about it.

    The sloth mini-ecosystem occasioned one of my favorite article titles: “Cryptoses choloepi: A Coprophagous Moth That Lives on a Sloth.”

    • Dominic
      Posted May 19, 2011 at 1:54 am | Permalink


      • Dominic
        Posted May 19, 2011 at 2:09 am | Permalink

        …though another reason to not to believe in a creator god – it would surely be more convenient for the sloth to defecate while in a tree than descend to the ground onece a week!

        I see sloths are also coprophagous –

        • Ichthyic
          Posted May 19, 2011 at 2:45 am | Permalink

          just checking… You do know why it is proposed that they climb down to defecate?

          If not:

          If they defecated from the tree they are in, it would alert ground dwelling, tree-climbing predators where they are like waving a bright red flag.

          they climb down to defecate so they can do it away from the tree they are currently hanging most in.

          they aren’t like monkeys, that move from tree to tree quickly.

          You probably knew this already, but just in case.

          • AR
            Posted May 19, 2011 at 7:52 am | Permalink

            Neat. I didn’t know this at all, so thanks! 🙂

          • Sven Dimilo
            Posted May 23, 2011 at 12:04 pm | Permalink

            just so

  4. colluvial
    Posted May 18, 2011 at 2:49 pm | Permalink

    From the shadows of the cars at the beginning of the video, it looked like there was no one to stop traffic and that it was going to be a sloth snuff film. Thankfully the guy on the motorcycle came by and knew how to pick it up.

    • Posted May 19, 2011 at 4:51 am | Permalink

      I was worried too. I watched it first to make sure the sloth made it before showing to my daughter.

      Those short back legs are really strange.

  5. freedtochoose
    Posted May 18, 2011 at 3:12 pm | Permalink

    It was a good stress test for me.

    • Posted May 18, 2011 at 4:11 pm | Permalink

      Ditto that! I sat there cringing the first half as every car went by saying “abunai! abunai!” (as if he could hear me telling him it was dangerous).
      I was struck by how clearly *well* adapted they are to living in trees by how pitiful they look on the ground.
      @Dominic– really long forelimbs! When they’re sitting in a tree, you don’t realize what a difference there is between the length of the forelimbs and the legs!

      Great video, Jerry–thanks! Will be showing this one to the kids since we (coincidentally) *just* watched a whole program about sloths on Animal Planet last weekend (where they went into the algae turning the hair green, the insects living off the algae, and so on). Sloths turned out to be much more interesting than ever I knew!

  6. Posted May 18, 2011 at 3:31 pm | Permalink

    That sloth looks a bit like me at the end of a marathon.

    • TrineBM
      Posted May 19, 2011 at 4:59 am | Permalink

      I looks a bit like me yesterday at the end of the 5 k race I participated in. (Trying to beat my own best time by running FAST the first three km.s – Stoopid)
      Sorry I laughed at you earlier, sloth. You could have had a good reciprocal laugh at me yesterday.

  7. Grania Spingies
    Posted May 18, 2011 at 3:33 pm | Permalink

    Is it just me, or does Motorbike Man’s sudden appearance remind you of Batman arriving in the nick of time to save the day?

    • Ichthyic
      Posted May 18, 2011 at 5:52 pm | Permalink

      It seemed to me like the scooter guy might have been wearing some kind of uniform?

      maybe some kind of park ranger type?

      • Ichthyic
        Posted May 18, 2011 at 5:53 pm | Permalink

        on second though, he might just be dressed to stay alive on the roads there (reflective vest, light shirt, etc.)

        • agentwhim
          Posted May 19, 2011 at 2:09 am | Permalink

          Sadly his protective clothing didn’t extend to trousers, gloves or a helmet.

          • Ichthyic
            Posted May 19, 2011 at 2:31 am | Permalink

            good point.

  8. Paul g
    Posted May 18, 2011 at 3:37 pm | Permalink

    What do the insects do for the sloth? Anything?

    • jay
      Posted May 18, 2011 at 5:03 pm | Permalink

      That is a key question. If there is no benefit to the sloth, then this is not symbiotic and could not be due to natural selection on the part of the sloth.

      • Ichthyic
        Posted May 18, 2011 at 5:57 pm | Permalink

        no, it is a form of symbiosis, it just might be of benefit to one party.

        mutualism: Both host and symbiont benefit

        commensalism: symbiont benefits, little or no host benefit

        parasitism: symbiont benefits to detriment of host

        Ammensalism: neither benefits, one is harmed.

      • Diane G.
        Posted May 19, 2011 at 12:00 am | Permalink

        jay, don’t know your age, but these definitions underwent a shuffle sometime after I left academia…sigh.

        • Ichthyic
          Posted May 19, 2011 at 12:29 am | Permalink

          these terms get more rigidly defined as we find more and more examples of each.

          I’ve seen modern bio curricula that still only include two, most commonly 3, and typically ammensalism is left off because of confusion as to whether it really represents a symbiotic relationship or not (it does).

          I think the basic terms were pretty well defined by the time I made it to grad school in the late 80’s, if not a bit sooner, but I can imagine a great deal of people not really being exposed to them unless they took a specific uni-level course in ecology or animal behavior.

          • Diane G.
            Posted May 19, 2011 at 1:00 am | Permalink

            I dropped out of grad school in ’72…Previously had been exposed to the terms rather a lot–did some undergraduate work on lichens.

            • Ichthyic
              Posted May 19, 2011 at 1:05 am | Permalink

              lichens are really interesting, IMO.

              It’s been one of the notable things I’ve been observing on my treks around NZ; with all the moisture here, you get ones that are just as interesting growing on buildings in the cities as you do miles away in the middle of nowhere.

              A quite common one tends to coat rocks and buildings with a bright orange carpet.

        • jay
          Posted May 19, 2011 at 8:25 am | Permalink

          yeah, I’m an old coot(61) , so that may play a part

          now get offa my lawn

    • Diane G.
      Posted May 19, 2011 at 12:07 am | Permalink

      According to this wikipedia short, not much!:

      Those of the heamatophagous guild are obviously parasites. The coprophagous spp would be at best commensalism; though one would think that at some of the population levels cited, they might be deleterious to the sloth.

  9. Posted May 18, 2011 at 3:39 pm | Permalink

    Q: Why did the sloth cross the road?

    A: (Answer will be posted November 18.)

    • Marella
      Posted May 18, 2011 at 11:08 pm | Permalink


    • Torbjörn Larsson, OM
      Posted May 19, 2011 at 6:31 am | Permalink

      To get to the sloth machine?

  10. Kudu
    Posted May 18, 2011 at 4:10 pm | Permalink

    The other people were just going to watch it get run over?

    I rescued a turtle off a busy road yesterday. I guess famously slow animals crossing the road is the theme of my week.

    I’ll be on the look out for a snail..

    • NoAstronomer
      Posted May 18, 2011 at 5:08 pm | Permalink

      Well at 0:18 they do say they’ll block traffic when the sloth actually gets to the road.

      • Kudu
        Posted May 18, 2011 at 6:01 pm | Permalink

        Ah, I didnt here that for some reason. Thanks.

  11. Tim Harris
    Posted May 18, 2011 at 4:24 pm | Permalink

    Inter-species altruism, Dr Coyne. And how do you explain that?!!! Or will you leave it to David Brooks…

    • Kudu
      Posted May 18, 2011 at 4:45 pm | Permalink

      To say that inter-species altruism doesnt make sense implies that the altruism response should be perfectly fine-tuned. Why should we expect it to be?

      Other evolutionarily programmed responses are frequently triggered by things that prove the response can be “tricked”. Feeling that a doll or teddy bear is “cute” is one example.

      Ive seen video of a light bulb or billiard ball placed near the nest of a duck sitting on eggs. The duck rolls the foreign object into the nest with the rest of the eggs.

      The response doesnt have to be perfect with regard to what triggers it to increase reproductive success.

    • jay
      Posted May 18, 2011 at 4:59 pm | Permalink

      I think that interspecies altruism is likely an artifact. Our altruism has not been ‘intelligently designed’ so that it fits one purpose, it’s a pattern of behavior to help other appealing looking (appealing in the sympathetic, not necessarily the beauty sense). The fact that it sometimes spills over to help members of other species is incidental.

      Note too that there is little evolutionary cost to this type of action so little to select against it. The human was at very little risk to himeslf… had the sloth been crossing by a mountain lion, I doubt the human would have been so helpful.

    • Posted May 18, 2011 at 5:36 pm | Permalink

      @Tim: That’s easy.

      1. Get filmed saving a cute animal

      2. Be seen on youtube by millions of chicks

      3 …

      4. Offspring

      • Tim Harris
        Posted May 18, 2011 at 9:22 pm | Permalink

        Thanks, Ralf. I think you’re the only one who realised that my comment was intended as a joke.

      • Torbjörn Larsson, OM
        Posted May 19, 2011 at 6:34 am | Permalink

        Chick dig sloths?

        Now you tell me! (Goes to untidy room.)

  12. sasqwatch
    Posted May 18, 2011 at 4:47 pm | Permalink

    Here’s one for Ben…

    Q: what’s the difference between a dead sloth in the middle of the road and a dead trombonist in the middle of the road?

    A: the sloth might have been on his way to a gig.

    • Posted May 18, 2011 at 6:43 pm | Permalink

      …and there weren’t any skid marks in front of the trombonist….


      • sasqwatch
        Posted May 18, 2011 at 6:55 pm | Permalink

        Ba-da-boom! (filing away for later).

  13. Jim Thomerson
    Posted May 18, 2011 at 6:51 pm | Permalink

    I think I read that sloths are the most abundant mammal in the jungle. I recall reading a note in BioTropica about two male sloths having a territorial dispute. The sloths were moving much faster than usual, and their speeds were given in sloth lengths per minute. I’ve only seen one sloth in the wild, but then I don’t spend much time looking up in trees.

    • jay
      Posted May 19, 2011 at 8:30 am | Permalink

      years ago I read an article (couldn’t remember where now) contrasting the sloth and the armadillo which evolved in the same environment.

      The sloth became highly specialized to the jungle environment, so while successful there, spread very little. The armadillo developed a more general strategy and spread widely outside the jungle where it evolved.

  14. Neil
    Posted May 18, 2011 at 7:08 pm | Permalink

    Q: Why did the sloth cross the road?

    A: He wanted to try life in the fast lane.

  15. Kieran
    Posted May 18, 2011 at 11:57 pm | Permalink

    Am I the only one thinking that the sloth at the end going WTF I didn’t know I could fly! Weeeee

  16. Alex, adv. diab.
    Posted May 19, 2011 at 12:30 am | Permalink

    > The poor beast can’t help it: the
    > species evolved before there were
    > roads!

    Well maybe, but I suspect Megatheria would have had less of a problem with crossing them.

    • Ichthyic
      Posted May 19, 2011 at 12:31 am | Permalink

      …or basically ignored the cars piling in to it as minor annoyances.


    • Posted May 19, 2011 at 1:18 am | Permalink

      AFAIK Megatherium (hypothetically) ate Glyptodons, which look like cars. If the floor of modern is thin enough, it might even find something to eat.

  17. Notagod
    Posted May 19, 2011 at 10:39 am | Permalink

    The christian will now need to forgo their worship of crossed death sticks. The video is clearly a message from one or several of the christian gods; the jebus was saved on Its way to the nail appointment, not during and not after. Also, the message is again clear as per usual, the jebus was treated with reverance prior to the appointment as It was picked up by Its scruff and flown first class to within feet of Its destination.

  18. Thanny
    Posted May 19, 2011 at 10:53 am | Permalink

    I was really puzzled by the way the guy picked up the sloth, because it didn’t match what physics requires would happen with a one-handed pickup of something that big. Then I read the bit about their fur being very long, obscuring their true size.

    I love learning interesting tidbits like that out of the blue.

3 Trackbacks/Pingbacks

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