Tetrapod Zoology

Shocking inter-racial sex scenes


During the breeding season male frogs are compelled to grab moving objects and engage them in amplexus, the tight ‘breeding clasp’ that occurs either under the forelimbs (axillary amplexus) or around the waist (inguinal amplexus), depending on the species. Amplexus is assisted by roughened pads of tubercles or even small spikes on the male hand, wrist and/or forearm. If it’s obvious that the moving object is not a female of the same species (because it feels wrong or makes an objectionable noise [as male frogs do when grabbed by other males]), the male lets go.

Nevertheless, male Eurasian common frogs Rana temporaria – the anuran I’m most familiar with – have been reported to grab goldfish, people’s hands and, as you can see from this photo, members of other anuran species. Here, a male R. temporaria has engaged in amplexus with a Common toad Bufo bufo: presumably a female based on size and colour (males are generally small and grey, females big and brown). I don’t know what the outcome of this photo was, but if mating occurred, there is no possibility of successful hybridisation between these very distant relatives.

Even more remarkable is the photo below (from wikipedia) in which a R. temporaria is clasping a very dead Fire salamander Salamandra salamandra. The salamander is dead now: was it that way when the frog first became interested in it? Obviously, male anurans don’t seem fussy when it comes to selecting mates. They literally grab at passing animals and hope for the best. By selecting a big, fat female full of eggs a male would be maximising his chance of reproductive success, but I really doubt if they’re that selective. Once in amplexus a male hangs on for days or weeks, and once the female gets to a pond the male then has to fend off competitors. Toads are far more aggressive than ranid frogs when it comes to this competition, sometimes forming large balls of fighting, kicking toads with one poor female in the middle. On occasion she may be drowned as a result.


Once spawning has occurred, it’s game over for the female and she leaves and gets on with her life. The male, however, may now try and find another female [insert hilarious quip about parallel with human behaviour]. In fact males spend so much time doing nothing but searching for, and grabbing hold of, females that they gradually starve and many of them die immediately afterwards (don’t forget, they’ve only just emerged from hibernation: here in England spawning used to begin in January or February but seems to be occurring earlier and is now sometimes reported in December). It’s recently been discovered that males can still fertilize eggs even if they fail to grab a female: they simply hang out near a spawning pair and shed their sperm into the water as the adjacent pair spawns. One egg clutch may therefore include embryos that have more than one father (Laurila & Seppä 1998). Even more amazing is ‘clutch piracy’: only reported in 2004, this is where males grab hold of egg clutches and then fertilize them as if they were mating with a female. In one studied population of R. temporaria, 84% of clutches were fertilized this way! How the hell did the frogs ‘realise’ that they need to shed sperm on eggs without the involvement of a female? The mind boggles.

Anyway, this was meant to be nothing more than a cheap joke and a picture-of-the-day, so I’ll stop there. Lest we forget, the global effort to prevent amphibian extinction [Tet Zoo introduction on that subject here] is still continuing: keep an eye on Frog Matters for the latest news. In the news right now is the discovery that atrazine – the second most widely used agricultural pesticide in the US – has been linked to anuran decline.

Thanks yet again to Markus Bühler for hunting out the neat pictures!

Refs – –

Laurila, A. & Seppä, P. 1998. Multiple paternity in the common frog (Rana temporaria): genetic evidence from tadpole kin groups. Zoological Journal of the Linnean Society 63, 221-232.

Vieites, D. R., Nieto-Román, S., Barluenga, M., Palanca, A., Vences, M. & Meyer, A. 2004. Post-mating clutch piracy in an amphibian. Nature 431, 305-308.


  1. #1 Jerzy
    October 31, 2008

    Yep, amorous male frogs grab almost all objects of approximately right size, including fish, plastic bottles and other rubbish etc.

    Males swimming away with unfertilized eggs is fascinating fact. Calls for a good sci-fi story about attics of externally-fertilizing aliens.

  2. #2 Neil
    October 31, 2008

    I have come across the scenario shown in the first photo, but with the actually female laying (toad) spawn, so she obviously wasnt that fussy either – but maybe thats just essex toads 😀

  3. #3 Bob O'H
    October 31, 2008

    Whilst we’re on cheap jokes, I co-authored a paper explaining this behaviour (pdf), which we called “Male Adaptive Stupidity”.

    The title was thought up before the female co-author joined us.

  4. #4 Dartian
    October 31, 2008

    Hmm. I would have thought that embracing a common toad or especially a fire salamander would be quite dangerous. Don’t they emit highly toxic body secretions?

    Incidentally, these pictures also illustrate the variability of colouration in Rana temporaria. (The individual that’s trying to do the toad is the more typical in that regard.)

    Oh, and hi Bob!

  5. #5 Hai~Ren
    October 31, 2008

    Here’s a similar sighting in Singapore.


    Male Asiatic Toad (Duttaphrynus melanostictus) trying to mate with introduced American Bullfrog (Rana catesbeiana), and a male bullfrog at that!

  6. #6 Darren Naish
    October 31, 2008

    Wow, talk about a bad match. Incidentally, if you’re using the ‘new’ generic name for the Asian toad, you may as well go the whole hog and use Lithobates for the bullfrog (which then becomes L. catesbeianus).

  7. #7 Hai~Ren
    October 31, 2008

    Darren: Ah yes, I meant to use Lithobates catesbeianus, but I’m a little unsure of what to make of this paper, which seems to propose that Rana be retained for the sake of utility.

    Hillis, D. M. (2007) Constraints in naming parts of the Tree of Life. Mol. Phylogenet. Evol. 42: 331–338. (Available for free here)

  8. #8 Robert Jaques
    October 31, 2008


    The most extreme case of this I’ve ever heard of.

  9. #9 Moai
    October 31, 2008

    Grrrrrr!! They called toads reptiles in the article that Robert Jaques posted. I realize that people in the general public aren’t as interested or knowledgeable in zoology as the readers of this blog, but for crying out loud, they should at least be able to classify common tetrapods into the correct class. Jeepers creepers!
    Ahem, anyway, your blog posts have been especially interesting lately, Darren. Keep up the good work.

  10. #10 David Marjanovi?
    October 31, 2008

    they should at least be able to classify common tetrapods into the correct class.

    Class? Piffle. They should learn what Amniota is!!!

  11. #11 Sven DiMilo
    October 31, 2008

    You want inappropriate amplexus? Here’s some inappropriate amplxus!

  12. #12 Bourgeois Nerd
    October 31, 2008

    He certainly looks pleased with himself, doesn’t he?

  13. #13 Rahne
    October 31, 2008

    This is so hot.

  14. #14 Chelydra
    November 1, 2008

    I have seen male Wood Frogs (Lithobates sylvaticus) in amplexus with significantly larger spotted salamanders (Ambystoma maculatum) and spring peepers (Pseudacris crucifer) much smaller than themselves. After the first breeding night last spring, I found several dead female peepers and a wood frog which I assume were drowned by the overenthusiastic wood frog males. I’ll have to try for photos this coming spring.

  15. #15 Mad Hussein LOLScientist, FCD
    November 2, 2008

    @ Sven: That truly gives a new meaning to the phrase “Yes we can”! LOL

  16. #16 Felicia Gilljam
    November 3, 2008

    How the hell did the frogs ‘realise’ that they need to shed sperm on eggs without the involvement of a female? The mind boggles.

    Umm… Isn’t that the way fish do it? Amplexus is the derived trait here, not shedding sperm directly on the eggs. And given how stupid the anurans seem to have gotten, it seems like going back to the old ways of doin’ things is a good idea!

  17. #17 Graham King
    November 22, 2008


    How the hell did the frogs ‘realise’ that they need to shed sperm on eggs without the involvement of a female? The mind boggles.

    Maybe the eggs smell of female. Or maybe the male remembers mating before and seeing eggs then, and now associates eggs with females, or simply with that earlier scenario (similarly-mating-mood-saturated). Associative memory, hormonal-state-facilitated.


    Hmm. I would have thought that embracing a common toad or especially a fire salamander would be quite dangerous. Don’t they emit highly toxic body secretions?

    Highly toxic… or highly arousing?!? (Couldn’t a substance be both?)

    [insert hilarious quip about parallel with human behaviour]

    Seriously, same comment applies. Maybe just a smell suggestive of ‘female’ (or similar enough!), and convenient shape, and seeming compliance, is enough to trigger mating response?

    [insert hilarious quip about parallel with human behaviour]

New comments have been disabled.