Thursday, May 27, 2010

The reign of rain frogs

An unfortunate aspect of growing up is that we lose our early sense of wonder. We quickly learn to name things and pigeon-hole them, and take them for granted. The world loses its sparkle.

But now and again, we encounter something that defies our expectations, and encourages us to marvel again.
A few nights ago I came across just such a something creeping around my cats' food bowls. I don't know if a cat had put it there (contributing toward its upkeep?) or if it trundled in by itself, but I usually only see them after rain.

It was a frog. The moment you read that, a preconception forms in your mind. Frogs hop. Frogs hang out near water. And they start life swimming about as tadpoles.
Forget it! I'm talking rain frogs.

This bushveld rain frog (Breviceps adspersus) is about one inch long, but they can grow to an impressive two inches. There are 14 different species creeping about South Africa.

Rain frogs spend their lives in holes, and they're shaped to fit. Their stumpy little legs preclude even a hope of hopping (a sensible safety precaution in a burrow dweller). At night, rain frogs crouch at their burrow entrances, licking up any bug that wanders past. And when it rains, they'll even come creeping out – slowly and cryptically – to find their own true love.

When agitated, rain frogs puff themselves up until they're almost spherical, and some species ooze a distasteful, milky fluid that deters potential diners. Photo by Jens Reissig and borrowed from here.

Being so portly and short-legged has its draw-backs; it makes reproduction tricky. Normally, a male frog mounts the female and clasps her in his arms (called amplexus) while he fertilises the eggs she's laying. But with rain frogs it's the ole 'corgi-mating-with-a-collie' problem. So how does the male manage? Fortunately, female rain frogs have it sorted. The skin on their backs secretes an adhesive, so the male only has to scrabble into position once, and he's set. Literally. The bond between them is so tenacious that you can't pull them apart without tearing the male's skin. Only after the pair has dug a burrow together, and the female has laid her 20-40 eggs inside, does her skin secrete a solvent that releases the male. Pretty nifty, huh?

Rain fogs dig their burrows while in reverse. They back into the hole-to-be, slowly revolving, and scratch out the soil with a special horny 'tubercle' on the heels of their hind feet.

Along with their other bizarre characteristics, rain frogs have given up on the whole idea of tadpoles. Their eggs consist of a large whitish yolk coated in thick jelly-like goo. The little rain frogs grow up within the safety of the burrow, sustained entirely by their egg yolk and bathed in fluid from the melting jelly. Only when they're fully metamorphosed frogs, do they creep out to face the world.

A bad day? This cape rain frog (Breviceps gibbosus) isn't feeling grouchy (actually I can't vouch for that). Its flattened face and forward facing eyes give it close-up, stereoscopic vision; all the better for nabbing small bugs. Photo borrowed from here.


  1. This has to be one of the most interesting articles I have read for a LONG time Lynda!! Thank you so much for it. What a cute little frog. I have unfortunately not come across one before but reading its habits, I can see why. It sure is something to go out hunting for next time I am near a river or dam and I'll bet I still won't find one. LOL!! It is like the elusive flower mantis I am searching for high and low and I bet I have walked right passed many. :)

    Well I cannot say much for its way of attaching men to their backs. :) But I guess if it works, it works. :) I would hate to have one stuck to my back though, then again... LOL!! Just kidding!!

    I find it interesting about the way they hatch their eggs too. Nature is wonderful once again!!

  2. Joan,
    I'm afraid that I see these little guys much more often than I'd like. The mongooses frequently dig them out and munch them with great enthusiasm. So much for their defence strategies!

  3. Hi Lynda, Thanks for sharing your great stories! We've visited Kampersrus near Hoedspruit when the roads were peppered with frogs... Where near Hoedspruit do you study? Would love to visit and learn more about what you do there. Also, is it possible to subscribe to this blog - to get your updates? Thanks!

  4. Deirdre,
    I've added a subscription box to the blog (over on the right) which hopefully works!
    I'm based about 30km north of Hoedspruit. Next time you're headed up this way, get in touch (my email is: and we can arrange something.

  5. What a fascinating alternative to the tadpole option for reproduction. Sounds like it's a highly developed adaptation for dealing with a very dry climate.

  6. Fabulous - I had never heard of their weird eggs or their amplexus alternative.

    Thanks for the great post,
    Bernard Brown

  7. Fascinating frog! And what a fascinating life you must lead.

    I am especially amazed at the puffed-up defense, though it sounds like it is not very effective against a determined mongoose.

    Thanks for this great post! This is my first visit, but I will drop by again soon.

  8. JSK,
    I'm not sure whether it's an adaptation to dry conditions or a means of avoiding aquatic predators. Although several rain frogs hang out in arid environments, a lot of species live in well-watered habitats. Either way, it must be very costly for Mum, who also hangs around the breeding burrow - protecting her investment - until the froglets complete their development.

    Thanks for dropping by.
    Rain frogs put a whole new slant on persuading males to 'stick' around.

    I wondered if the puffed-up defence (rather than being a size bluff) was designed to wedge the frog firmly inside its burrows, thus making it difficult for non-digging predators to extract it.

  9. Fascinating to read about so many adaptations of such a small animal. You must be watching carefully to notice such detail.

  10. Cindy,
    Hi, nice to hear from you.
    I'm afraid I'm no frog expert; other people have done the careful watching to glean these facts. I just watch in horror as they're munched by mongooses!

  11. I believe that if humans spent as much time truly observing as is devoted to meddling with things the world be in much better shape. Your blog is one of the places that continually elucidates this, with humor and humility.

  12. Retrun,
    Thank you for the lovely compliment. Sadly, finding funding for observational studies is almost impossible these days. Experimental meddling is the 'in thing'.


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