What Do Poisonous Caterpillars Look Like?

Caterpillars, which are in the larval stage of butterflies and moths, aren’t much liked. They’re rather considered a nuisance as they eat through your plants. But, it could be worse as some of them as poisonous. So, what do poisonous caterpillars look like?  

Poisonous caterpillars are often brightly coloured to warn predators of their poison, and they’re covered with several quills or spikes that hold toxins. 

Caterpillars have poisonous stings and barbed hooks to protect themselves from predators, and like most insects, if they have poison, they’ll have bright colours to indicate it.

Predators stay away from them if they notice bright colours. However, most species of caterpillars actually have these quills or spikes for intimidation and show only and don’t have toxins in them.

Several other stinging caterpillar species are poisonous, however, and not only do their quills hurt but cause painful symptoms but they may also contain venom. That’s why it’s important to determine what is a poisonous caterpillar and what isn’t.

What Colour Caterpillars are Poisonous?

Poisonous caterpillars are of varying shapes, sizes, and bright colours. These bright colours are often in patterns, stripes or spots.

Poisonous caterpillars are mostly of bright, vibrant colours like the bright green saddleback caterpillar or the spiny oak slug caterpillar.

Some of them may have dull colours, but they always have several quill-like hairs on certain portions of their body, or their body is entirely covered with spikes and hair, such as the flannel moth caterpillar. 

Are Caterpillars Naturally Poisonous?

Most poisonous caterpillars are naturally poisonous right after they hatch from their eggs. They have quills or spines to inject their poison. Their quills are also intimidating, and predators often stay away from spiky caterpillars.

Certain species of caterpillars become poisonous by eating poisonous plants. Plants such as milkweed plants can make caterpillars poisonous as caterpillars store whatever they eat, and in the case of a milkweed plant, they can store its poison. 

Are All Caterpillars Poisonous?

No, not all caterpillars are poisonous. There are around 180,000 species of caterpillars across the globe, each with its own appearances and traits. Some of these will be poisonous, others won’t be.

What are the Most Poisonous Caterpillars?

There are several spiky caterpillars that are known to be very poisonous. They’re of varying shapes and colours. Each poisonous species of caterpillars will cause varying effects on a person upon getting in contact with it. Here are the top 4 most poisonous caterpillars:

Puss Caterpillar

Megalopyge Opercularis, the puss caterpillar, is an inch in length and is completely covered with long soft hair that makes it look very fluffy and cute.

In the United States, the puss caterpillar is also called the Southern Flannel Moth caterpillar and despite its cute, fluffy appearance, it is considered the most poisonous caterpillar.

Upon contact with the spiny hairs of this caterpillar, its spines release poison into your skin that causes pain immediately and a burning sensation. The sting victims also get rashes and swelling and may have headaches, nausea, fever, and low blood pressure.

Some victims may even get sick to the point of getting hospitalized. 

Io Caterpillar

The io moth caterpillars are bright light green in colour, and they have narrow white and red stripes going along their bodies. This makes identifying these caterpillars easier.

They’re entirely covered with tiny green spines all over their bodies. These green spines look like tiny trees or plants growing on their skin. These spines look interesting, and you would want to touch it probably, but it’s best to avoid contact with these caterpillars as their spines are very poisonous.

They get dislodged and become embedded in the skin, causing a burning and stinging sensation upon contact with them. 

Saddleback Caterpillar

Saddleback caterpillars are very common in the US, and they’re very easy to identify. It has a bright green patch on the middle of its back like a saddle, the green patch has a big brown spot in the middle, and the green patch is surrounded by a white border.

It has two brown corners and has a pair of fake eyes on one side to intimidate predators. It has fleshy protrusions that are covered with several tiny spikes, and both of these protrusions are on each end of its body.

If you accidentally touch one without knowing it’s poisonous, it causes a painful sting that causes irritation, swelling, and pain in the sting area. Certain people that are a little more sensitive may get nausea or headaches, and it will last for a couple of days. 

Saddleback Caterpillar

Bag Shelter Caterpillar

The bag shelter caterpillar is a unique caterpillar that travels in long lines with other caterpillars of its species.

They’re highly dangerous as, upon being touched, they will cause external but also internal bleeding. In a few cases, a person can even bleed to death because of them. Even if a stray hair comes your way and you accidentally inhale it, it will cause respiratory problems. 


Caterpillars may have a harmless appearance, and they can’t bite you. And most of them are simply harmless pests, but certain species of caterpillars are equipped with thorns, quills, spikes, and hairy exteriors to protect them from predators, making them dangerous for you. It’s best to identify poisonous caterpillars, so you avoid touching them.

The most notable identification of poisonous caterpillars is their bright colouring and spiky and thorny exterior, which makes them look different from other caterpillars. If you want to get rid of caterpillars then do so with caution.

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