Martha:

Fantastic observation ! Yes violence among toads during mating is reported from elsewhere such as in this link:

http://www.researchtrend.net/jnbr/VOL%203(3)%202014/2%20BL%20Narayana%20JNBR%203(3)%202014.pdf

Best

Syed

Hi Syed, RG didn't seem to be able to accept my answer, but I made a screen dump so here you can read my reply.  I so  appreciate your quick response. 

Martha:

I am just a casual observer of Nature. For about 3000 Million years the Life on Planet Earth was a peaceful affair. It all started during Phanerozoic era about 650 Million year ago when violent killing or be killed became routine affair and continues till today. Peace and Violence exists in nature and one should view this as absolutely normal and acceptable. I fully support your viewpoint Martha, and have a wonderful time critically observing Nature.

Best

Syed

Sorry Martha but didn't received the alert via email of your interesting question.

As you know I am not an Amphibian specialist but I would go for the first hypothesis.

Will come back shortly with expert's opinion.

Cheers

You found my question anyway! I'm so glad. After reading Syed's article, I feel as if this is something else we share with animals. Our violent streak! We get frustrated and we lash out. I'm now voting for either the raccoons or the toads. I don't really think the fish (largest about 6-8 inches long) would be capable of tearing a frog apart.

Hi Syed, yes, my big passion is studying the habits of animals, especially insects and spiders. My back yard has many small ecosystems that I've been watching for a couple of years. I spend most of my time either outside taking pictures or cropping and enhancing pictures. Thursday night I'll be giving a talk called "Nature in the Small". I will introduce various small communities, and then some more general relationships between different parts of the yard. The day after the talk I will release it as a website so everyone can see it. This is the first time I've talked to a group of people about my passion. I hope some children will come. I developed this love as a child. If I had had a camera then like my present one (not the greatest but good enough for most practical purposes). This is my first insect picture that I took with my "baby brownie" back about 1950.  I will show this picture in my talk so kids can know they can start from the bottom!  This is also the first time I was mentioned as an entomologist.  Scotty wrote this in my memory book at the end of 7th grade.  :-)

Amphibians expert  opinion: 

"Hello , hard to say for toads . As a rule , however, when there are massacres of this kind it is due to some predator. Corvids are more sophisticated: surgically opening the toxic animal bodies ( such as salamanders , newts , toads ) and eat the viscera (liver and usually lungs ) . If they can also be raccoons do not know. " (Cannibalism and gold fishes are excluded)

Thanks Francesco,

The bodies didn't seem to be eaten.  Just maimed and dead.

In my opinion a predator (even a dog or a cat) killed them but felt they are poisonous hence left them. If pressed, I would confirm your first hypothesis.

Francesco, who is the person who answered the quesion for you?  Or does he/she want to be anonymous?

On page 40 of the book "Frogs: The Animal Answer Guide" by Michael E. Dorcas, Whit Gibbons there is a subsection "Do frogs fight?" (see the first link below), and the following description is given:

"We seldom think of frogs as fighting one another, but some species of frog actually use physical combat in social interactions. The large African bullfrog (Pyxicephalus adspersus) is well known for violent fights among males at breeding time. …"

As for African bullfrog, see the second link below.

https://books.google.co.jp/books?id=cST6P7aJToYC&pg=PA40&lpg=PA40&dq=violence+among+toads+during+mating&source=bl&ots=1aD1rMB0Kf&sig=T3iPnrX5nOcLOpXuCCQQkC_4wvs&hl=en&sa=X&ved=0ahUKEwjU-fW4q-LMAhXEJqYKHe2SC_EQ6AEIIjAB#v=onepage&q=violence%20among%20toads%20during%20mating&f=false

https://en.wikipedia.org/wiki/African_bullfrog

Dear Tatsuo, thank you so much for your reports.  I don't want to think it's true, but it really does sound as if it fits the facts of this case.  The next time the toads gather for  mating, I plan to sleep out next to the pond (or rather stay awake as much as possible) and monitor the situation.  I've already bought an outdoor extension cord so that I can run an unobtrusive light device to make photographing them easier.

They usually do this gathering twice a summer, and the current devastation took place at the time for the first meeting.  It will be a month or two before they try again.  I'll keep people posted through this question.  Thanks to everyone who has helped to document this behavior.  

Martha

I have never seen frogs or toads of similar size dismember a conspecific such as you describe. Certainly some anurans will feed on others that can fit in their mouth. I vote for a predator, such as raccoons. I have heard (or read) of some predators of toads that avoid their parotid glands when feeding upon them.

Well, they have started trilling now - haven't heard that since the massacre - I will spend as much time as possible tonight watching for bad behavior.  I don't have a great camera for zooming but I'll do what I can to see what goes on.  Wish me luck!

Here is what happened since Wednesday May 27, 2016.

http://mokennon.albion.edu/2016/toads%205%2025%2016.htm