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Broadleaf weed with purple flowers growing among grasses

In Okla­homa, where I grew up, one of the first plants to show green in the spring was Lami­um amplex­i­caule, which we called hen­bit. This lit­tle plant is in the mint fam­i­ly, although it does­n’t smell “minty” (or even “sagey” or “orega­noesque” like oth­er mem­bers of the family).

Hen­bit and oth­er mem­bers of the genus Lami­um are also called dead-​nettles. This had always puz­zled me, because when they came up in the spring, they were one of the few plants “alive”, green and growing.

small weed growing in gravelly soil
Sting­ing nettle

One day I rode Veron­i­ca down to the grass and weeds on the slope below the are­na, where she likes to graze (until it all turns brown in the late spring). Both she and Bud­dy had encoun­tered Urtica ure­ns, the annu­al sting­ing net­tle. Both were stung on the lips, and both decid­ed they weren’t inter­est­ed in that plant any more.

Veron­i­ca reached down for a patch of what appeared to be sting­ing net­tle. I told her, “I don’t think you’re going to like that,” but as she ate it, I real­ized it was dead-​nettle, and the light bulb went on. It (and oth­er mem­bers of the genus Lami­um) super­fi­cial­ly resem­bles sting­ing net­tle, but it does­n’t sting—it’s “dead”.

Head of foxtail grass
Mouse bar­ley

Now if I had looked it up in Wikipedia, I would have learned that, but instead I learned it because a horse has a very dif­fer­ent view of plants than a per­son, even if that per­son is a botanist.

I’m a botanist. You prob­a­bly guessed that from the title and the sci­en­tif­ic names. I’ve been for­tu­nate in being paid to teach botany to col­lege stu­dents for around four decades. But I’ve nev­er stopped learn­ing, and in this as in so many oth­er areas, hors­es have been my teachers.

Bud­dy prefers mouse bar­ley (Hordeum mur­inum) over slen­der wild oat (Ave­na bar­ba­ta). Mouse bar­ley is the com­mon­est source in my region of the fox­tails that get caught in dogs’ fur, ears, and nos­trils. Bud­dy eats it before it’s ripe and break­ing apart, when the grains are sweet and soft.

Horse eating weed
Bud­dy eat­ing Ital­ian thistle

He loves Ital­ian this­tle (Car­du­us pyc­no­cephalus), which is relat­ed to arti­choke, and sow this­tle (Sonchus oler­aceus) and prick­ly let­tuce (Lac­tu­ca ser­rio­la), both let­tuce rel­a­tives. If we ignore the “beards” of the bar­ley, the spines of the this­tle, and the bit­ter milky sap of the last two, these are plants we would eat. The fla­vor palettes of a horse’s palate are dif­fer­ent from ours, but not total­ly alien.

Yellow flower head
Sow this­tle

Most botanists today don’t spend a lot of time with hors­es. But it wasn’t always so. The ear­ly botan­i­cal explo­ration of west­ern North Amer­i­ca by botanists of Euro­pean ances­try was most often car­ried out on horse­back, with pack mules. I won­der what they learned from their hors­es and mules. Was the knowl­edge that I’m now dis­cov­er­ing once com­mon­place, in a world where equines were com­mon­place? Or were the old-​time botanists as like­ly to look to their hors­es for guid­ance as I am to look to my truck? Many of their jour­nals still exist, and so per­haps we could learn, if we looked, and if they both­ered to write about it.

Group of yellow flower heads of a weed
Prick­ly lettuce

My days of botan­i­cal explo­ration are large­ly in the past. And there are real advan­tages to 4WD vehi­cles. But the view from a horse, and with the horse’s world in mind, should be part of the expe­ri­ence of every botanist.


Hors­es see a dif­fer­ent world than we do, in large part because of spe­cif­ic dif­fer­ences in their eyes. This arti­cle will focus on one aspect, the way horse and human eyes react to the col­ors of illu­mi­na­tion used for enhanc­ing human night vision. If you’re not inter­est­ed in the details, you can skip straight to the rec­om­men­da­tions.

Like humans, hors­es have two types of light-​sensitive cells in their reti­nas (the reti­na is the light-​sensitive lay­er at the back of the eye). Rods are sen­si­tive to very low lev­els of light, but don’t dis­crim­i­nate col­ors. Cones do the col­or dis­crim­i­na­tion, but need more light than rods to do their job. In humans, rods are about a hun­dred times more light-​sensitive than cones, and there’s no rea­son to expect hors­es to be any dif­fer­ent. Vision involv­ing the cones is called pho­topic vision and vision involv­ing the rods is sco­topic vision.

Photopic vision (colors)

Humans have three dif­fer­ent types of cone cells that absorb light of three dif­fer­ent wave­lengths: 420 nm (nanome­ters), which appears blue, 534 nm, which appears green, and 564 nm, which appears red. These are “peak sen­si­tiv­i­ties”; each type of cone detects wave­lengths short­er and longer than its peak, and there’s some over­lap. We have “trichro­mat­ic vision”, and all the dif­fer­ent col­ors we per­ceive are the result of our brains pro­cess­ing the sig­nals from these blue, green, and red cones.

Humans and oth­er pri­mates are unique among mam­mals in hav­ing trichro­mat­ic vision. Hors­es, dogs, and oth­er mam­mals have only two kinds of cone cells, and dichro­mat­ic vision. In hors­es, blue-​sensitive cones are most absorp­tive at 428 nm, and the oth­er type of cone is sen­si­tive at 539 nm, which appears yellow-​green to us. Some humans have protanopia, a type of color-​blindness in which the red cones don’t func­tion; a horse sees the world much like that.

Impor­tant for our pur­pos­es here, the yellow-​green cone can’t detect light with a longer wave­length than around 640 nm, which is a deep red.

Scotopic vision (“night vision”)

Hors­es have excep­tion­al night vision rel­a­tive to humans. Their eyes are larg­er than most oth­er land mam­mals, to gath­er more light. They have a tape­tum lay­er that reflects light back onto the reti­na (this is what caus­es eye­shine). And their reti­nas are rich­er in rods. In envi­ron­ments with moon­light, starlight, or even reflect­ed city lights, hors­es can see well enough to walk, trot, or even gal­lop with­out run­ning into things.

When a rod absorbs light, its visu­al pig­ment (rhodopsin, or “visu­al pur­ple” in old­er ref­er­ences) is irre­versibly changed (“bleached”), so that the cel­l’s abil­i­ty to detect light is reduced until new rhodopsin is syn­the­sized. In low light, rhodopsin is regen­er­at­ed as fast as it is used, but a burst of bright light can bleach all the rhodopsin in all the rod cells, and it can take thir­ty min­utes or more for the cells to ful­ly regain their abil­i­ty to func­tion. For rea­sons that are not entire­ly clear to me, humans regain a use­ful lev­el of night vision with­in five min­utes of being exposed to bright light, but hors­es need the full thir­ty min­utes. The same horse that can run across a pas­ture under the quar­ter moon can­not eas­i­ly dis­crim­i­nate details in a dark horse trail­er when asked to enter it from bright daylight.

Illumination for night vision

Humans have poor­er night vision than many oth­er ani­mals, and there are sit­u­a­tions where it’s advan­ta­geous to main­tain night vision even in the pres­ence of illu­mi­na­tion. There are two dif­fer­ent approach­es in cur­rent use.

The first to be devel­oped was the use of red light. Rod cells are insen­si­tive to red light, so they can stay adapt­ed to low-​light con­di­tions even while the red cone cells form images. Red night­time illu­mi­na­tion is still used in avi­a­tion and some mil­i­tary set­tings, and in dis­plays of some elec­tron­ic devices.

Red light has a cou­ple of dis­ad­van­tages for this use: it requires a high­er bright­ness, since it relies on pho­topic vision, and it’s some­times dif­fi­cult to dis­crim­i­nate shapes and near­ly impos­si­ble to dis­crim­i­nate colors.

A new­er alter­na­tive is to use bluish-​green light, at about the peak sen­si­tiv­i­ty of rod cells. Because this is the light that rods see best, extreme­ly low inten­si­ties can improve sco­topic vision with­out destroy­ing dark adap­ta­tion. In a sense, it’s like car­ry­ing around a full moon.

The effect of these two types of light on hors­es is total­ly dif­fer­ent. Like humans, hors­es can­not see red with their rod cells, but they also can­not see it (or see it only dim­ly if it’s more of an orange-​red) with their yellow-​green cone cells. A human anal­o­gy is an infrared remote for an enter­tain­ment sys­tem: most peo­ple can­not see the beam even if it is shin­ing direct­ly in their eyes. For hors­es, deep red is “infra-​yellow-​green”, not real­ly a per­ceived col­or at all.

Horse's eye open under red light on left, squinting under green light on right
Red light pre­serves hors­es’ night vision. At a bright­ness lev­el high enough to be use­ful to humans, green light impairs their night vision.

And because hors­es have more rods, and more sen­si­tive rods, than humans, a low-​intensity bluish-​green light, bare­ly per­cep­ti­ble to a human, would be much brighter to a horse, and would reduce their night vision.


  1.  Red light pre­serves both human and horse night vision. Hors­es only see it dim­ly if at all, and con­tin­ue to rely on their superb night vision. It allows humans to per­ceive shapes and see text and dia­grams that would be much less vis­i­ble with the infe­ri­or human night vision, but at the same time pre­serves that night vision for see­ing in areas where the beam is not directed.
  2. The bluish-​green light used for enhanc­ing human night vision is inap­pro­pri­ate for hors­es. It is only effec­tive for pre­serv­ing night vision in humans at the low­est lev­el of bright­ness that a human can use­ful­ly per­ceive, and this is much brighter that the low­est lev­el that a horse can per­ceive. If the human can see it, the horse’s night vision is already impaired.
  3. Red head­lamps or flash­lights are use­ful for night trail rid­ing; they have no effect on the horse’s night vision, and aug­ment the human’s night vision. The use of white light head­lamps or flash­lights is strong­ly dis­cour­aged; they destroy night vision in both hors­es and humans in exchange for pro­vid­ing only a nar­row area of illu­mi­na­tion, and when they are switched off, hors­es need much longer to regain night vision than humans, and are effec­tive­ly stum­bling in the dark until they do.
  4. Red LED illu­mi­na­tion may be more use­ful for barns and out­door sta­bles than the usu­al flu­o­res­cent light­ing. It allows a human to deal with a spe­cif­ic horse with­out destroy­ing the night vision of all the oth­er hors­es in the facil­i­ty. Hors­es dif­fer in their response to “hav­ing the lights turned on”, but even for the most non­re­ac­tive horse, it’s one more thing to put up with. In my ide­al facil­i­ty, there would be red light illu­mi­na­tion every­where that would go on with a sin­gle switch, so I could walk down the aisle with­out trip­ping on some­thing. Each stall could have an indi­vid­ual white flood lamp, or I could car­ry a white head­lamp or flash­light, if I need­ed bet­ter vision for a spe­cif­ic horse.

Exec­u­tive sum­ma­ry: Red light, yes. Green light, no.


Not all the time; that would be silly.

There’s a dog­ma among rid­ers and train­ers that a horse should move at the gait and speed that you choose, all the time, every time, and that any devi­a­tion is dis­obe­di­ence or “dis­re­spect”. Allow­ing the horse to rou­tine­ly choose gait, speed, or path is def­i­nite­ly dan­ger­ous, and a skilled rid­er should be able to clear­ly com­mu­ni­cate expec­ta­tions to the horse. But by being absolute and unyield­ing in your expec­ta­tions of the horse, you are cut­ting off one of the most use­ful ways your horse has of com­mu­ni­cat­ing to you.

At lib­er­ty, hors­es almost always choose their own gait and speed. Even a horse  run­ning with a herd is choos­ing the safe­ty of that herd. About the only excep­tions are a horse being chased by a real or imag­ined preda­tor, and a horse stuck in quick­sand. Stud­ies have shown that hors­es often choose gaits and speeds that are most effi­cient; this is hard­ly surprising.

Adding a rid­er to the mix changes every­thing. When a horse deals with the weight and bal­ance of the rid­er, dif­fer­ent gait/​speed com­bi­na­tions become more effi­cient. Com­bi­na­tions that are not effi­cient have to be trained. Clas­si­cal west­ern hors­es have to be trained to the jog, which is slow­er than the trot they might choose them­selves, and to the lope, which is slow­er than their pre­ferred can­ter. Upper-​level com­pet­i­tive dres­sage hors­es are trained not only to slow­er speeds, such as the can­ter pirou­ette, pas­sage, and piaffe, but also extend­ed trots. It’s true that some hors­es and even breeds have con­for­ma­tion that makes these com­bi­na­tions eas­i­er, but that does­n’t mean that they are in any way effortless.

So what might a horse be com­mu­ni­cat­ing by choos­ing a gait and speed that you did­n’t ask for? The stock answer is “I’m the boss of you!” Some rid­ers and even train­ers are so inse­cure in their con­nec­tion with hors­es that they always seize that expla­na­tion. Some­times it’s even cor­rect. But what if the horse had no incli­na­tion to be the boss of you yes­ter­day, and is per­fect­ly coop­er­a­tive tomorrow?

Some oth­er things your horse might be telling you:

  • I hurt. I’m devel­op­ing an abscess, or my arthri­tis is act­ing up.
  • I’m not strong enough to do this for an extend­ed period.
  • I’m scared. If you weren’t on my back, I’d run away, but I’m doing this dis­place­ment activ­i­ty instead.
  • I’m grumpy, my ovaries hurt, and I’m doing every­thing I can not to buck you off, which I’d nev­er do anyway.
  • I feel great! I want to run in the sun, pow­er through the flow­ers, and I real­ly don’t under­stand why you’re not down with that.
  • I feel great! I want to nap in the sun, munch on the flow­ers, and I real­ly don’t under­stand why you’re not down with that.
  • You’re crazy! You’re ask­ing me to risk los­ing my foot­ing and killing us both.
  • You’re throw­ing me off-​balance! I hear there are these things called “lessons”.
  • I’m sick. If you took my tem­per­a­ture, or even looked at my eyes, you’d real­ize that.

If my horse were try­ing to tell me any of these things, I’d want to know about it. Var­i­ous hors­es at var­i­ous times have told me most of these things. If I passed it all off as dis­obe­di­ence, I’d be telling my horse “You don’t mat­ter.” That’s not a good basis for a trust relationship.

If I passed it all off as dis­obe­di­ence, I’d be telling my horse “You don’t matter.”

One of the trails Bud­dy and I take away from the sta­ble has a gen­tle incline right as we leave the prop­er­ty. He always wants to trot it. If I ask him to walk, he will, but I don’t, because I can learn enough from the speed of that trot, the way his body moves, and the way his head moves to know whether there are any issues that I should address, or that might mean we should­n’t go out at all. And the time he vol­un­teered a walk, I could tell he was­n’t well, and we turned around and went back.

And then there’s the stop.

It’s true that hors­es can stop because they are lazy. Or exhaust­ed. Or wor­ried. Or con­fused. It’s hard to imag­ine a response that use­ful­ly address­es all those things (and more) with­out know­ing (or even car­ing about) the reason.

When I first rode Bud­dy in what I like to call “con­trived obsta­cle cours­es”, he would some­times stop dead before an obsta­cle. I was green, and there was peer pres­sure, and I even thought about get­ting spurs. But I learned that if I kept him fac­ing the obsta­cle with­out push­ing him to go for­ward, he would even­tu­al­ly fig­ure it out and go for­ward on his own, because he knew that’s what I expect­ed. And once he real­ized that he would­n’t be kicked at every obsta­cle, he calmed down and took them more easily.

So if your horse insists on a dif­fer­ent gait or speed from the one you request­ed, think about let­ting him take it for a few strides until you fig­ure out why. Remem­ber that hors­es live in the present. Your horse does­n’t plot dis­obe­di­ence based on your past weak­ness­es. Give him the chance to tell you what’s on his mind, now.

Life worries: horse, food and more food; owner, a bunch of different things
Cour­tesy of Horse Net­work, for­mer­ly Horse Collaborative

And chick­ens. And moun­tain lion shad­ows, which can skulk inde­pen­dent of their lions. And miss­ing sta­ble mates...Oh! There you are! What a relief! And stallions...I’ve heard rumors. And water cross­ings, espe­cial­ly with mud. And that same tree.



This post is inspired by and ded­i­cat­ed to Veron­i­ca, a mare’s mare, who reminds us that for hors­es, safe­ty always comes before food.


In their herds, hors­es main­tain a social frame­work of friend­ship, dom­i­nance, and lead­er­ship. Much has been writ­ten about this. But that’s not what this post is about.

Mark Rashid has writ­ten about hors­es want­i­ng to fit into “our” herd. Left unstat­ed is that the result­ing herd con­sists of both humans and horses.

I think it’s impor­tant to note that I am a firm believ­er that hors­es prob­a­bly don’t, nor will they ever, see us as a mem­ber of their herd. Rather, I believe it is just the oppo­site. I think hors­es do every­thing they can to fit into “our” herd.
—Mark Rashid

Just as we can mis­in­ter­pret hors­es as oth­er humans, hors­es in the com­bined “our herd” inter­pret us as hors­es. Some horses/​people are dom­i­nant, and some are sub­mis­sive. Some are lead­ers, and some are fol­low­ers. Humans can act kind of screwy some­times, but real­ly there’s no oth­er way to see them than as real­ly strange hors­es (or as real­ly gnarly preda­tors, but that’s not where we’re going with this).

Vir­tu­al­ly every eques­tri­an agrees that humans need to be the lead­ers. Most hors­es are look­ing for lead­ers, and it ill suits them or the peo­ple around them when they think they have to be in charge to stay safe. A very few hors­es are nat­ur­al lead­ers, and it ill suits the peo­ple around them to allow them to take this role with humans. And it’s part of the train­ing of every eques­tri­an to be a leader of horses.

We humans also have social hier­ar­chies, and we don’t put those away when we are around hors­es. And a use­ful instructor–student rela­tion­ship requires that the stu­dent defer to the instruc­tor, at least dur­ing the lesson.

The prob­lem comes when an assertive instruc­tor dom­i­nates a sub­mis­sive stu­dent, and the horse decides the stu­dent is of low­er rank than he is. We’ve all seen hors­es in lessons defer to the instruc­tor rather than the rid­er, and this is only natural—the horse is look­ing for the per­son in charge, and that’s the instruc­tor. But if the instruc­tor should leave the are­na, the horse should always look to the rid­er. If the instruc­tor so thor­ough­ly dom­i­nates the stu­dent as to low­er the stu­den­t’s sta­tus to less than that of the horse, the instruc­tor has failed, no mat­ter how much teach­ing or ego grat­i­fi­ca­tion might have gone on.

It’s easy to watch for this, and for many instruc­tors it’s easy to cor­rect the prob­lem, by build­ing up the dif­fi­dent stu­dent in the eyes of the horse. For instruc­tors with­out that abil­i­ty, or who are chal­lenged by the dif­fi­dence of a par­tic­u­lar stu­dent, the solu­tion is to help the stu­dent find an instruc­tor who can work with them.

Putting peo­ple below hors­es, inten­tion­al­ly or inad­ver­tent­ly, has no place in horsemanship.


No, not for shav­ing whiskers.

In phi­los­o­phy, a razor is a prin­ci­ple or rule of thumb that allows you to elim­i­nate (“shave off”) unlike­ly expla­na­tions for a phe­nom­e­non. Per­haps the most famous is Occam’s Razor: “Among com­pet­ing hypothe­ses, the one with the fewest assump­tions should be select­ed.” But one of my favorites is Han­lon’s razor: “Nev­er attribute to mal­ice that which can be ade­quate­ly explained by stupidity.”

Bud­dy taught me Bud­dy’s Razor the hard way, for both of us. I regret a lot of the mis­takes I made along the way, but he says he’s just glad that I final­ly fig­ured it out.

Nev­er attribute to defi­ance any­thing that can be ade­quate­ly explained by pain, fear, or miscommunication.
—Bud­dy’s Razor

If I had a dol­lar for every time some­one told me “He’s not respect­ing you! Don’t let him get away with that!”, I still would­n’t have quite enough for all the vet bills, but it sure would make a dent. There are two big things wrong with that atti­tude. First, hors­es are inca­pable of respect—it requires a lev­el of abstract thought that they don’t have. Peo­ple load a lot onto the term “dis­re­spect” when they apply it to hors­es, but the part I’m refer­ring to here is bet­ter called “defi­ance”. The sec­ond prob­lem with the state­ment is that cor­rect­ing a horse for “defi­ance” is only use­ful it you have cor­rect­ly iden­ti­fied it, and in most oth­er cas­es is counterproductive.

It’s true that hors­es are some­times tru­ly defi­ant, most often for one very spe­cif­ic reason—a horse may judge your posi­tion in the over­all social hier­ar­chy of humans and hors­es to be low­er than his (more about this in anoth­er post), and so feel no need to fol­low your direc­tion. But more often, the appear­ance of defi­ance is a result of pain, fear, or miscommunication.


Most hors­es are bet­ter than most peo­ple at not show­ing pain. This is adap­tive for a prey ani­mal, since a preda­tor is more like­ly to attack you if you appear inca­pac­i­tat­ed in any way. But it caus­es us to miss signs of pain, and in many cas­es we inter­pret as “defi­ance” the reac­tion to pain.

When I was learn­ing the basics of equi­tation with Bud­dy, one of the exer­cis­es was the 20 m cir­cle. He did well in a cir­cle to the left, so it was puz­zling that he would fall to the out­side on the cir­cle to the right. The instruc­tor had me try the tra­di­tion­al cor­rec­tions, but they did­n’t have the “tra­di­tion­al effect”. It turned out that he had an arthrit­ic right hock, so it caused pain for him to reach under his body with the right hind on the cir­cle, and he respond­ed by falling to the out­side. When his arthri­tis was treat­ed, the prob­lem went away.


Hors­es sur­vive by fear and flight. It’s a won­der that they work with humans at all. There are plen­ty of jokes about hors­es being “afraid of sil­ly lit­tle things”, but when you ask a horse for some­thing and he says “No way!”, it’s not so sil­ly, and it’s not defi­ance. Forc­ing a horse against fear works often enough that peo­ple still do it, but it has long-​term disadvantages.

You can nev­er rely on a horse that is edu­cat­ed by fear. There will always be some­thing that he fears more than you. But, when he trusts you, he will ask you what to do when he is afraid.   —Antoine de Pluvinel


As much trou­ble as peo­ple can have com­mu­ni­cat­ing with one anoth­er, you’d think that they’d expect even more mis­com­mu­ni­ca­tion with a dif­fer­ent species. But just as the stereo­typ­ic Amer­i­can tourist shouts Eng­lish at peo­ple who don’t under­stand it, to make it more com­pre­hen­si­ble, many rid­ers respond to a horse not under­stand­ing by “shouting”—increasing the force of the aids, or mov­ing on to punishment.

The order of Bud­dy’s Razor is impor­tant. First, rule out pain. If that’s not the prob­lem, rule out fear (and pain can cause fear, since a painful horse can­not escape dan­ger as eas­i­ly). With both those ruled out, check to make sure you’re com­mu­ni­cat­ing. If the horse is not in pain, not afraid, and is being asked for some­thing he has already shown he knows how to do, only then should you assume defiance.