Are horse chestnuts poisonous?

[JLM27]

Does anyone know if squirrels eat horse chestnuts? Are they harmful?

[CritterMom]

My understanding is that ALL PARTS of horse chestnut are toxic.

[stepnstone]

All parts of horse chestnut bark, flower, leaves and seed are toxic and
contain a poison called esculin and can cause death when eaten raw.
Oddly enough it is used to make medicine for various treatments.

[JLM27]

Thanks, guys. We were always told as kids that they were poisonous to us, but I didn't know if that applied to squirrels. They can eat raw acorns and we can't, you see, so I didn't know.

[hilllin1]

I am a beginner squirrel rescuer, caring right now for my first two baby squirrels ever, and am a brand new subscriber to the Squirrel Board forum, in need of every form of advice for my two babies. Nevertheless I have some experience with horse chestnuts and squirrels, and have wanted very much to offer what information I can.


My yard has four large horse chestnut trees. It also has many squirrels, Fox Squirrels specifically. Over the years, people walking past on the sidewalk in the Fall often admire the beautiful fallen chestnut nuts and ask if they can collect some from the ground to take home as Fall decorations. I always say Yes. Such passersby also frequently ask whether these chestnuts are edible, knowing perhaps that some species of chestnuts are indeed edible, or perhaps thinking of the old popular Bing Crosby Christmas song, Chestnuts-Roasting-On-An-Open-Fire. I figured I had better find out in order to know how to answer them. So I looked into it.


The advice I found (through the Internet) is that horse chestnuts and other parts of the horse chestnut tree are "mildly toxic". Quoting from Wikipedia: "The seeds, especially those that are young and fresh, are slightly poisonous, containing alkaloid saponins and glucosides. ...Raw Horse Chestnut seed, leaf, bark and flower are toxic due to the presence of esculin and should not be ingested. Horse chestnut seed is classified by the FDA as an unsafe herb.[12] The glycoside and saponin constituents are considered toxic.[12]"


That reference, #12, is cited as "Horse Chestnut, Memorial Sloan-Kettering Cancer Center". Not that it tells you how to find it. Note the phrasing "slightly poisonous". Not "deadly". Also, the comment on ingesting might just refer only to people.


So I tell people that horse chestnuts are considered "slightly toxic", which is the phrase I found at that time, now 16 years ago. I suggest that it might not be a good idea to eat them, and I suggest they can pursue the question further if they are interested. I also say that the squirrels in my yard eat the chestnuts every year and do not seem to suffer any ill effects.


So my report is that the squirrels in my yard eat the horse chestnuts, bury them for eating through the winter, appear to eat the buds and bark of the chestnut trees, build and live in nests made of chestnut leaves within the chestnut trees, and possibly birth and raise babies in those trees (although I am not certain about that. There are other trees in the yard, and possibly mother squirrels do not choose to have their babies in the chestnut trees.). I have never seen a squirrel fall dead from a chestnut tree; on the contrary, the squirrels on the property are very healthy indeed. Possibly they know how much horse chestnut material to eat without becoming sick; in the case of the nuts, perhaps they wait into the winter for long enough (as suggested in the Wikipedia quote) for the toxic elements to have dissipated. Possibly there is simply no problem in the first place.


I have offered a few horse chestnuts of the current crop to my two babies, now about 12 weeks old. I worried a bit about giving the nuts to such young squirrels, but I decided that their nestmates, loose in the yard, are encountering the chestnuts on the ground now and so I want my two babies to have the same opportunity. It is well, I decided, for them to be familiar with the chestnut nuts now, before they are released later.


Not to contradict the other responders here, I just wanted to post my observations and experience.

[Anne]

Hillin1, I do believe that you are going to be an asset to the board.:hug:clap!:Welcome So very glad you have joined us.:wave123

[island rehabber]

Hillin1, I do believe that you are going to be an asset to the board.:hug:clap!:Welcome So very glad you have joined us.:wave123

Ditto that. Excellent info, Hillin1.
I believe I read something similar in one of my squirrel books -- that horse chestnuts are not toxic to squirrels, raccoons, wildlife but are mildly toxic to humans.

[hilllin1]

Thank you! I'm flattered, especially so, sinbce you are such prominent experts in this community. Not sure I deserve such praise. Since posting yesterday, I found a website that said that horse chestnuts are quite toxic to horses (What! Then they should be called Non-Horse Chestnuts.), even life-threatening to them, which I had not known. I also felt guilty for passing on mere anecdotal information when I have no expertise to be instructing others. I'm also horrified to learn last night of UnicornGirl's awful experience with acorns. Wish I had known of that; I could have cited it in my answer.


I also had to contemplate what the meaning of "mildly toxic" is, after all. Shouldn't even mildly toxic materials be avoided? But we eat spinach, Swiss chard, rhubarb, and other plants that can be called "mildly toxic" to us --their oxalic acid content is the trouble: it is at best anti-nutritional, since it blocks the absorption of B-vitamins. The solution in that case is not to eat those things to excess.


What, after all, is the upshot of my posting, for those who want to know how to regard horse chestnuts for squirrels? It is, I suppose, "Golly, I dunno, but my wild squirrels eat them." And, you probably don't have to purge your squirrels' world of horse chestnuts if some are there. And, your squirrels know more than you do, and they know how to judge (See comments in the thread from UnicornGirl). Most important, it seems to me, is to ground yourself in the established absolute fundamentals of what you must feed your squirrels, what you can safely feed them, and what you must not feed them; there is plenty of healthy, fresh, safe, complete nutrition that you can provide for your babies within those constructs. There is no need to feed them horse chestnuts at all, and no need to enter a potential grey area where maybe not enough is known, or at least that you yourself don't yet know.


If you feel you need a more definitive answer, stay on it. Stay alert and keep yourself informed. Reflect by analogy on what is known about acorns. (It's so scary, what happened to UnicornGirl, that she seemed to be well informed and to be on very established solid ground in her practice of feeding acorns. Awful.) Inquire. There are wonderful specialists to consult (not me), such as animal nutritionists, food safety experts, biochemists, food technologists. They might even be pleased to be asked, or to recommend someone else. The FDA knows a lot about humans, and maybe they have people who know about animals or can recommend someone.


That's about all I can think to suggest at this point. Thanks for the chance to reply to you, the chance to offer an encore of sorts.

[hilllin1]

From www.horsechestnut.com (!) here is information on the saponin toxin in horse chestnuts and, for us, a specific statement about squirrels:


"The nuts contain high concentrations of a saponin-class toxin called Aesculin, which is toxic to many animals including humans because it causes hemolysis (destruction of red blood cells). The saponin can be eliminated by leaching the pulverized nuts in multiple changes of boiling water, to yield a wholesome starchy porridge once important to some Native American tribes. Some animals, notably deer and squirrels, are resistant to the toxins and can eat the nuts directly. An interesting side-note is that Aesculin is a natural pH indicator which, when extracted turns from colourless to fluorescent blue under UV light in an acidic pH range."


Very interesting how native Americans learned to wash away the toxin.


So (according to that site, anyway) squirrels can eat the nuts directly! The toxin does not affect them! Great news for us.


I will continue to look for information.

[hilllin1]

There is a different site www.horsechestnuts.com with an "s", apparently a site that sells horsechestnut products.

[hilllin1]

Something about the suggestion of washing horse chestnuts in multiple changes of water, and the reports that raw horse chestnuts taste very bitter made me wonder if the undesirable chemicals in horse chestnuts are related to those in quinoa.


One is advised to rinse quinoa grains in multiple changes of water before cooking them. Quinoa tastes very bitter if you don't.


I found a site, http://www.glutenfreegigi.com/questionable-quninoa-perfect-plant-protein-or-poison/ , that talks about why to rinse quinoa before cooking. It also goes into quite a satisfying explanation of the occurrence and chemistry of saponins in food plants.


Bingo! : saponins are indeed the chemicals that make quinoa bitter and that one needs to rinse away before cooking the grain.


So! horse chestnuts and quinoa have some of the same undesirable chemicals in them. Quinoa, then, offers another example of us eating foods that are "mildly toxic" for us, this one's problems being closely related to those posed by horse chestnuts.


BTW, one site I consulted said that, at the time that horse chestnuts were given a name in the English language, in, like, the 16th century, the term "horse" meant "strong", "sturdy", etc. So horse chestnuts are named for that trait, not because horses eat them.


I also saw reports that squirrels, deer, racoons, wild turkeys, and domestic cows like to eat raw horse chestnuts without being harmed by the chemical compounds in question, but that pigs won't touch them. They are also reportedly not good for dogs.


Just as in UnicornGirl's threads about acorns, chestnut sites say that if you are going to prepare chestnuts (either horse or the sweet edible ones) for eating, you should discard any that have wormholes in the shell, are moldy on the inside, are shriveled or dried-up inside, or have large voids of air inside the shell. Maybe this is what the technique of discarding any acorns that float in water (as mentioned in UnicornGirl's acorn discussion) is also about. And maybe also what squirrels are testing for as they consider whether to eat one. Dunno.


'Nuff.