Frog defense: hiding, fighting, or both

JAC: Instead of “Readers’ Wildlife” today, we’ll have a report on frogs by Greg Mayer, who’s just visited Costa Rica.


by Greg Mayer

Although quite cryptic on the forest floors it calls home, the smoky jungle frog (Leptodactylus pentadactylus) in the photo below is too obvious to be a candidate for “spot the frog”. This large species of frog (reaching over a 150 mm in snout-vent length) sports what in the military would be called “defense in depth”– a series of defensive behaviors and adaptations that help the frog avoid becoming someone else’s meal. The one in the photo below I encountered at the Lapa Rios Ecolodge, near the tip of the Osa peninsula, on my recent trip to Costa Rica.

Smoky Jungle Frog (Leptodactlyus pentadactylus), Lapa Rios Ecolodge, Osa, Costa Rica

Smoky Jungle Frog (Leptodactlyus pentadactylus), Lapa Rios Ecolodge, Osa, Costa Rica

It was a large individual (well over 100 mm), and we found it at night in the rainforest. Its first line of defense is that it’s quite hard to see against the variegated mixture of brownish leaves, twigs, and mud of the forest floor. (The red shine of the eye is more noticeable, but fortunately for the frog, natural predators don’t carry flashlights!) When first seen, the frog was sitting up at attention, but when we approached, it pushed itself down flat against the substrate, and as I moved around in front of it for a picture, it really pushed its face into the ground, making itself less noticeable.

Smoky Jungle Frog (Leptodactlyus pentadactylus), Lapa Rios Ecolodge, Osa, Costa Rica

Smoky Jungle Frog (Leptodactlyus pentadactylus), Lapa Rios Ecolodge, Osa, Costa Rica

Since all we wanted was pictures, the frog did not move to its further lines of defense. Had we provoked it, it would have assumed an elevated defense posture, with the back raised, also inflating its body and expelling air to make a hissing sound, similar to what is seen in some toads (Leptodactylus is not a true toad).  I haven’t seen (or at least can’t recall seeing) this in Leptodactylus— the behavior was described in this species by Jaime Villa (1969)– but I have seen it in giant toads.

Elevated defensive posture of Leptodactylus pentadactylus (Villa, 1969: Fig. 6).

Elevated defensive posture of Leptodactylus pentadactylus (Villa, 1969: Fig. 6).

This of course draws a potential predator’s attention to the frog– having hidden, why would it now face up to its foe? This is where the next lines of defense come in. First, the frog is big, and this behavior makes it look even bigger. For some predators, the frog is a mouthful too far. Next, if the frog is touched, it exudes a copious and toxic mucus. This mucus induces a strong allergic response in humans, and presumably others, at least mammals if not all other vertebrates- intense sneezing, watery and itching eyes– the unpleasantness of which I can attest to from personal experience. It is said that people merely in the vicinity, who have not touched the frog, can, through aerial transmission of toxin droplets, get the same symptoms. The mucus can irritate the skin, and cause pain to any scratches or open wounds (which I fortunately did not have when catching the frogs). And the frog will also emit a loud, piercing shriek, which might well startle a predator into releasing its grip. Norm Scott reported that caimans were attracted to this cry, and even speculated that that was its function– to attract caimans to dispatch the frog’s predator– sort of like a bugle call to the cavalry!

More straight forward than the multi-layered defenses of the smoky jungle frog is the defense of poison dart frogs– aposematic, or bright, warning coloration, accompanied by very toxic skin secretions. We encountered two species at Lapa Rios. Phyllobates vittatus, with bright orange stripes, is a member of the genus which contains the three species of the poison dart frog family, Dendrobatidae, that are actually used by Indians to make poison darts.

Poison Dart Frog (Phyllobates vittatus), Lapa Rios Ecolodge, Osa, Costa Rica

Poison Dart Frog (Phyllobates vittatus), Lapa Rios Ecolodge, Osa, Costa Rica

We found three of them, during the day, along the Rio Carbonero. We also found three Dendrobates auratus along the paths at the Lodge itself, wandering about during the day, bold as brass, as is their wont. I’ve seen them quite abundant in other parts of Costa Rica, but we saw only three during 4.5 days at Lapa Rios. For neither species of dart frog was I able to get a very good picture; there’s a better picture of auratus in an earlier post, and, in another earlier post, more details and references on poison dart frogs. BBC Earth has a nice explainer on poison dart frogs, with links to interesting papers

Poison Dart Frog (Dendrobates auratus), Lapa Rios Ecolodge, Osa, Costa Rica

Poison Dart Frog (Dendrobates auratus), Lapa Rios Ecolodge, Osa, Costa Rica


Savage, J.M. 2002. The Amphibians and Reptiles of Costa Rica: A Herpetofauna between Two Continents, between Two Seas. University of Chicago Press, Chicago

Scott, N.J. 1983. in D.H. Janzen, ed. Costa Rican Natural History. University of Chicago Press, Chicago

Villa, J. 1969. Comportamiento defensivo de la “Rana Ternero”, Leptodactylus pentadactylus. Revista de Biología Tropical 15:323-329. pdf

11 Comments

  1. infiniteimprobabilit
    Posted June 4, 2016 at 7:52 am | Permalink

    “the smoky jungle frog (Leptodactylus pentadactylus) in the photo below is too obvious to be a candidate for “spot the frog”.

    Really? Well I couldn’t see it till I blew up the photo, and then only because its eye is open.

    cr

    • infiniteimprobabilit
      Posted June 4, 2016 at 8:05 am | Permalink

      “when we approached, it pushed itself down flat against the substrate, and as I moved around in front of it for a picture, it really pushed its face into the ground, making itself less noticeable.”

      It assumes if it can’t see you, you can’t see it? This is starting to remind me of the ravenous bugblatter beast of Traal. http://h2g2.com/entry/A387029

      cr

    • Posted June 4, 2016 at 8:57 am | Permalink

      I did consider making it a “spot the ..”, preparing a copy of the photo with the “red eye” edited out, but decided it was still too easy to see.

      GCM

  2. Posted June 4, 2016 at 6:26 pm | Permalink

    Reblogged this on The Logical Place.

  3. Posted June 4, 2016 at 7:32 pm | Permalink

    Reblogged this on My Selfish Gene and commented:
    It’s easy to think of animals as detached players in a drama that they never know they participate in. This nice write-up of frog defense by Greg Mayer on Why Evolution is True shows that is not true. What would you do if you saw a toad rise up on all fours and start hissing?

    • infiniteimprobabilit
      Posted June 4, 2016 at 7:49 pm | Permalink

      “What would you do if you saw a toad rise up on all fours and start hissing?”

      Stop licking toads?

      cr

  4. Posted June 4, 2016 at 7:35 pm | Permalink

    Are there any non-toxic frogs in the area with the aposematic colourings of poison dart frogs? Certainly there are a number of instances of mimicry among venomous snakes, where non-venomous species look quite similar to certain venomous species.

  5. Mark Sturtevant
    Posted June 4, 2016 at 7:44 pm | Permalink

    Very cool stuff! I find frogs in particular to be pretty amazing in their range of colors and other survival tricks.

  6. Posted June 6, 2016 at 7:39 am | Permalink

    Cool stuff, thanks! And: Lucky you!

  7. Dominic
    Posted June 15, 2016 at 4:56 am | Permalink

    Reading a week late – thanks Greg – very interesting 🙂


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