Are Acorns Toxic to Squirrels? | What To Know

Most squirrels eat many acorns without trouble, yet spoiled, bitter, or moldy acorns can cause stomach upset and, at times, serious illness.

A squirrel cracking an acorn looks like nature’s simplest snack. Oaks drop food. Squirrels eat it. Done.

Still, acorns aren’t equal. Some are sweeter. Some are loaded with tannins that taste sharp and can irritate the gut when eaten in big runs. Some sit in wet leaf litter long enough to rot. That’s when people start asking if acorns can harm squirrels.

You’ll get a clear answer early, then the details that matter in a yard: which acorns raise risk, what “bad” looks like, warning signs, and what to do if a squirrel seems unwell.

Are Acorns Toxic to Squirrels? The Real Risks

In normal wild feeding, acorns are a main food for many tree squirrels. A healthy adult often handles them fine. Risk rises with quality problems and repetition: green acorns, high-tannin acorns eaten day after day, or any acorn that has started to spoil.

A squirrel has built-in habits that lower risk. It sorts acorns by taste, caches them, and switches foods across seasons. Backyard conditions can break that pattern by keeping squirrels in one damp spot with one steady pile.

What’s Inside An Acorn That Can Cause Trouble

Acorns are seeds, and oak trees defend them with plant compounds. The main group is tannins. Tannins taste astringent and can bind with proteins, which can make digestion rougher when intake is high.

Tannin load shifts by oak group. White oak acorns tend to be less bitter. Red oak acorns are often more astringent. That’s one reason squirrels commonly eat white oak acorns sooner while storing red oak acorns longer.

Maturity matters, too. Green acorns and young oak parts can carry higher levels of the compounds linked with oak poisoning in many animals. Veterinary toxicology references note that heavy exposure to green acorns can trigger gut irritation and kidney injury in susceptible species. Quercus poisoning in animals lays out that pattern across species.

Squirrels are not grazing livestock, and acorns are a normal part of their diet. Even so, the chemistry still applies: a squirrel already dehydrated, injured, or stressed has less wiggle room if its food is harsh on the gut.

Why Spoilage Beats Tannins As A Backyard Problem

Tannins are a “dose” issue. Spoilage is a “one bad nut” issue. Wet acorns soften, then fungi move in. Some fungi can produce mycotoxins, which are chemicals that can harm animals. The U.S. FDA page on mycotoxins describes these mould-made toxins and why they matter in nuts and grains.

You can’t test an acorn for mycotoxins at home. Treat visible mould, sour odour, mushy texture, black dust, or a hollow “paper shell” feel as a discard signal.

How Squirrels Lower Risk With Natural Habits

Squirrels don’t eat acorns like a person eats chips. They work them over.

• Sorting. They often choose less bitter acorns when options exist.
• Caching. Buried acorns can lose some bite as moisture moves through the shell.
• Nibbling. If an acorn tastes off, they may drop it after a few bites.
• Food switching. Seeds, buds, fungi, and berries share the menu when available.

Backyards change the game. A feeder keeps squirrels near one spot. A big wet acorn fall under one oak can create a steady, repeating food source, including nuts that have started to rot.

When Acorns Are Most Likely To Make A Squirrel Sick

Most yard worries fall into three buckets: green acorns, monotony, and spoilage.

Green Acorns And Bitter Loads

Unripe acorns can be harsh on the gut. A squirrel may still eat them if other food is thin. Loose stool and reduced eating are common early signs.

One-Item Diet Runs

A squirrel that keeps returning to one stash can end up eating the same kind of acorn for days. That raises tannin load and can set up dehydration if diarrhoea starts.

Mouldy Or Rotten Caches

Hidden piles under decks, in gutters, or in damp corners can turn into rot clusters. The squirrel may keep going back out of habit.

Backyard Steps That Cut Risk

You can’t stop squirrels from eating acorns, and you don’t need to. You can remove the worst conditions that turn acorns into a problem.

1. Target wet piles. Rake shaded, damp spots where acorns stay soft.
2. Remove spoiled nuts. Bin mushy, sour, or mouldy acorns fast.
3. Keep feeders clean. Old seed and hulls trap moisture and can grow mould.
4. Offer fresh water. A shallow dish, changed daily, helps during dry spells.
5. Find cache hotspots. Check under steps, planters, and tight corners for hidden stashes.

These steps work because they break the repeat-exposure loop. A squirrel can handle a lot, yet repeated bites from the same rotten pile is where things go sideways.

Acorn Risks And What To Do

Situation	What It Can Lead To	What To Do
Dry, mature acorns from clean ground	Low risk for healthy squirrels	Leave it alone; normal feeding is fine
Green or unripe acorns	Gut irritation if eaten in big amounts	Rake heavy piles; don’t hand-feed green acorns
High-bitter acorns eaten day after day	Rough digestion, dehydration risk if diarrhoea starts	Reduce easy access to one stash; keep water out
Acorns that feel soft or spongy	Decay and fungal growth	Dispose promptly; clear damp stash spots
Acorns with visible mould or sour smell	Possible mycotoxin exposure	Remove and bin; stop leaving food out overnight
Large hidden cache in a damp corner	Rot spreading through the pile	Remove the cache; block access to the cavity if safe
Squirrel seems ill right after eating from one pile	Repeat exposure can worsen symptoms	Clear the pile; disinfect feeder areas with hot soapy water
After storms, acorns soaked under one tree	Fast spoilage	Rake often for a week; compost removed acorns
Pet or rehab squirrel fed acorns as a main food	Repeated tannins and stale storage risks	Keep acorns as a small treat; store dry and fresh

Signs That Point To Acorn-Related Upset

Wild squirrels hide weakness, so small changes matter. Acorn-related trouble most often looks like gut upset plus dehydration.

Digestive Changes

• Loose stool or sticky fur around the tail base
• Dropping food after a few bites
• Hunched posture while resting

Dehydration And Weakness Signs

• Staying on the ground or sitting low for long periods
• Slow movement, heavy breathing, or glassy eyes
• Cold, limp body posture in mild weather

Seizures, bleeding, or inability to stand are emergencies. Those signs can come from injury, poison bait, infections, or heat stress.

What To Do If A Squirrel Looks Sick

You can’t diagnose a wild squirrel from a porch, yet you can do a few practical things that reduce harm.

Remove The Suspect Source

Rake up wet or spoiled acorns. Dump old seed from feeders. If you find a damp cache, remove it so the squirrel can’t keep dosing itself.

Offer Water, Skip Food Piles

Put out a shallow dish of fresh water and refresh it daily. Avoid leaving piles of nuts “to help.” Extra food can draw more squirrels and spread sickness.

Recheck Later The Same Day

Mild gut upset can pass with rest and water. If the squirrel stays grounded, looks weak, or worsens by evening, it needs hands-on care.

Contact A Licensed Wildlife Rehabilitator

Wildlife laws differ by place. Licensed rehabbers can give fluids, check injuries, and handle toxins safely. If you can share what the squirrel ate and where the stash was, that helps.

Fast Triage Guide For Backyard Observations

What You See	What You Can Do Now	Urgency
Loose stool, still active in trees	Remove wet acorns and old feeder seed; set out clean water	Low, recheck later
Hunched, slow, stays on a low branch	Clear spoiled acorns; keep pets indoors; watch from distance	Medium, recheck in 2–4 hours
On the ground, weak, easy to approach	Keep people and pets away; contact a rehabber	High, act the same day
Breathing hard, hot day, mouth open	Place water nearby; create shade at a distance; call a rehabber	High, act now
Seizures, bleeding, or can’t stand	Call a rehabber or wildlife agency at once	Emergency
Multiple squirrels ill in one spot	Remove all food sources; clean feeders; call wildlife agency	High

Feeding Acorns On Purpose

If you want to offer acorns as a treat, stick to dry, firm, mature acorns that smell clean. Skip green or soft acorns. Keep portions small, and don’t leave acorns on wet ground.

If you want to help squirrels long-term, the best move is simple yard hygiene: keep food dry, remove rotten stashes, and keep a fresh water option available.

A Simple Rule That Prevents Most Problems

If an acorn is firm and smells like a nut, a squirrel can usually handle it. If it’s soft, wet, sour, or dusty, treat it as trash and remove it.

So, are acorns toxic to squirrels in day-to-day life? Most often, no. Trouble comes from spoiled nuts, green acorns, or a repeat stash that pushes the gut too far.