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The alleged three-headed frog
The BBC news item, Puzzle over three-headed frog (originally titled "'Warning' over three-headed frog") spawned this story that swept the news media and the weblog circuit over the week following March 5th 2004. Briefly: staff and pre-school children at the Green Umbrella day nursery, Weston-super-Mare, UK, found the above. After they'd taken photos and a video, it escaped and was never found. The BBC took up the story, citing one of their own wildife experts, biologist and presenter Mike Dilger, as "stunned" and saying "it could be an early warning of environmental problems" (they published the same factoid in their CBBC Newsround children's section). From there, the tale snowballed to newspapers worldwide. Here's a slideshow of images at local6.com, and videos appeared at CBS News and ITV West. But was it really a three-headed frog, or a hoax as some have suggested?
Short answer: neither. In my view, this is just multiple amplexus, typical frog and toad mating behaviour.
Amplexus
Mating of Anurans (frogs and toads) involves the male tightly clasping the female - this is called amplexus - for hours or even days, prior to externally fertilising her eggs. So we know what we're talking about, first check out these images of frog amplexus. The grip is very strong; the male develops special pads on his thumbs to hold on, and won't let go even if the couple is picked up and handled. Axolotlman comments (merci aussi!) in this Les Monde des reptiles thread, Grenouille tricéphale, that some frogs secrete during amplexus an adhesive mucus so sticky that it's impossible to separate them without tearing the skin.
Multiple amplexus
Commonly, more than one male grips the same female. For comparison, see these very clear photos of a frog three-way and frog four-way, from David Jones' excellent photo-journal Frog and Pond Diary. Note the early March date of these: in southern England, frogs spawn at this time of year, which supports the amplexus theory. With toads, multiple amplexus can be be spectacularly weird, as toads generally have many more males than females attempting to breed, My favourite so far is this wonderfully gross picture of a toad mating ball involving at least six toads (by HotShot - merci! - of the Presence PC forum).
So, the appearance of the supposed three-headed frog is entirely consistent with multiple amplexus. Have another look at David Jones' photo of frogs in embrace, and then study the above. I interpret it as a smallish female frog A being clasped by two larger male frogs B and C. The visible arms belong to A; those of B and C are hidden because they're underneath clasping A (though B's fingers are visible under A). The legs of A are hidden because it's smaller than the frogs on top, though there are toes showing below the left underside of C that may be A's left foot. There are four normal back legs in view: both legs of C and the right leg of B are on the ground, while B's left leg is lying on top of C.
Misinterpretation?
Amplexus has been misinterpreted before by untrained observers, who didn't recognise it and thought the animals were joined together. See this article by Bernd Heinrich mentioning how "a woman once brought a thus engaged wood frog couple to [him], thinking it was a two-headed frog", and this Massachusetts MetroWest Daily News report, Girl finds two-headed toad in Hopkinton, that turned out to be Mating toads, not mutants. In the Metro News story it's interesting to read the complicated, and completely mistaken, analysis of the situation: "Its front legs have grown into the back of the larger frog, and it appears the bottom jaw may be connected to the larger toad's head". Eyewitness descriptions and deductions, then, can be unreliable.
However, according to newspaper accounts, this new case has also been endorsed by wildlife experts. I am sceptical even of this, because it appears that the BBC's experts weren't given the full picture and certainly haven't correlated all the available evidence. One important point is that some of the photos clearly disprove the claim of six legs (four at the back and two at the front). The Weston Mercury picture with its account, Six-eyed monster, - and even more clearly, the Sun photo below - Frog's a triple jumper - show a further foreleg (apparently C's front left arm unclasped). What appears to be two fingers of B's left hand are also visible.
Other photos also show protruding digits suggesting hidden limbs, such as this detail of C's left side with what's probably A's left foot underneath.
One thing I find very strange is that there are no pictures of the underside. The Sun photographs show someone was perfectly capable of picking the frog{s) up, and it looks like deliberate avoidance of a viewpoint that could disprove the six-legs description.
Other problems with three-headed frogs
If this were a three-headed frog as photographed, it would require a completely unprecedented teratology. I think the BBC experts would have difficulty justifying the combination of circumstances.
1) Conjoined siblings are genetically the same individual. There have never been any substantiated examples of non-identical conjoining. These frogs are non-identical; the head and arms A are much lighter in colour than B and C; and the back of C appears a slightly different colour to B. (The occasional cases of apparently conjoined non-identical multiples, such as the kittens picture half-way down this page, are generally considered to arise by their being stuck together after birth by dried mucus, etc).
2) Although triple monsters have been described, the evidence mostly anecdotal. A three-headed turtle was reported from Taiwan in 1999, and there's another videoed on YouTube (here) but these appear to be better described as a two-headed turtle - standard left-right bifurcation - with an unclear structure - probably a stump of conjoined limb or shoulder bone - between the heads. Two heads is as far as it goes; two-headed tadpoles have been created in the laboratory (for instance, by exposure of embryos to lithium or inducing overproduction of the wnt gene) and there's anecdotal evidence of two-headed frogs observed in the wild. The US Geological Survey Field Guide to Malformations of Frogs and Toads (PDF format) has no examples, but I've been sent one current example of a two-headed toad (see below).
3) The angle of the alleged conjoining is wrong. Conjoined siblings are generally joined - or branched - symmetrically about the body axis (the wnt gene involved specifically causes left-right axial bifurcation). B and C might conceivably be conjoined, but you don't get positioning like A, with the back of one conjoined to the belly of the other.
4) If, as speculated, the deformation was caused by pollution, it doesn't match known frog teratology from this cause, which involves single individuals with problems such as missing limbs, missing eyes and obviously abnormal extra limbs (the jury is still out on the relative contributions of chemical pollution, infection by parasitic trematodes, and maybe UV levels). See the website of the Minnesota Pollution Control Agency for examples.
5) It seems vastly unlikely that such a trio would manage the necessary feeding, locomotion and avoiding predators to successfully grow from tadpole to adulthood.
Of related interest: Kentaro Mori of the excellent Brazilian skeptics weblog CetismoAberto kindly sent me a reference to two-headed Surinam toad for sale at a Tokyo rare aquatics shop for 498,750¥ (about $4600 / £2500), and apparently found in the wild.
Why?
I have no idea why this story has spread so dramatically, with the majority of news sources copying it without critical or scientific analysis. The Independent, as far as I can tell, was the only one to mention the mating-frog possibility - 'Thee-headed frog' leaves experts on the hop. Perhaps the environmental angle - mutation caused by pollution - is the emotional hook. But there's also something very mediaeval about it: monstrous births presaging disaster. In this Frogs.org article, Hidden Agenda, Russell Wangersky points out the interplay of factors that can drive a story like this (in fact, the previously mentioned two-headed toad one). My inclination was to think that the BBC deserves a slap on the wrist for rushing into publication without more stringent checking and then, unlike the MetroWest DailyNews, failing to report counter-evidence. But then again, this is an unimportant regional 'curiosity' story where lack of highly detailed checking is understandable. I e-mailed them straight away, criticising the facts of their coverage, but so far they've neither posted a follow-up, amended the story, nor replied to me. If you're a herpetologist and agree with my interpretation, maybe you could offer the BBC a reasoned refutation.
It took about four years to get a reply.
| Addendum: 14th April 2008 Approximately on the 4th anniversary of the story, I sent a further complaint to the BBC - and got a reply. Discussion, reproduced with permission, follows: Mon, 14 Apr 2008 15:11:10 +0100 / From BBC Fri, 18 Apr 2008 20:59:32 +0100 / From Ray Girvan Mon, 21 Apr 2008 08:23:32 +0100 / From BBC Mon, 21 Apr 2008 13:09:25 +0100 / From Ray Girvan Mon, 21 Apr 2008 14:11:56 +0100 / From BBC Date: Mon, 21 Apr 2008 16:24:17 +0100 / From Ray Girvan Wed, 23 Apr 2008 09:03:10 +0100 / From BBC And there the exchange stands. It's probably pointless to complain further at this stage, but it makes an interesting case study of how the BBC works in going against its own claimed guidelines - "All the relevant facts and information should be weighed to get at the truth ... checking and cross checking the facts" - to cling to a biologically stupid story. If you're a herpetologist and agree with me about the likely explanation, do contact the BBC. Maybe you can do better. , after reading this, I've convinced you that the BBC story is garbage, please contact them. The story address is http://news.bbc.co.uk/1/hi/england/somerset/3534361.stm and the complaints link is here. |
To finish on a relevant, but lighter, note: from Channel 4 Films, Frog Porn. This comic short by Graeme Kennedy features a seething pondful of spawning frogs with a soft porn backing sound track.
