are caterpillars poisonous

Are Caterpillars Poisonous? + World’s Top 5 Poisonous Caterpillars

Caterpillars are most likely to show up in your garden around late summer and early fall. They can ravage certain vegetables and leaves, but they will often stick to one kind of plant, and they also have many natural predators.

But even as you ponder how to control them, are caterpillars poisonous? Caterpillars may not necessarily be poisonous – but they have hairs or spines that can cause pain, itching, rashes, burning, blistering, and swelling when they come in contact with human skin.

Read also: 6 Most Common Caterpillars in Florida

How to Tell if a Caterpillar is Poisonous

Fuzzy and colourful caterpillars can appear cute and fascinating, but it is critical not to be fooled by their appearance. Many fuzzy caterpillars with urticating hair and spikes on their body are either poisonous or venomous.

These stinging caterpillars are becoming a difficult problem in America, particularly in several southern states like Florida and the Midwest. 

The buck moth caterpillars, Saddleback caterpillars, lo moth caterpillars, and puss caterpillars are some of the most venomous caterpillars in the United States. 

The lo moth caterpillar has a red and white stripe that runs on the lateral sides of its body. Naturally, the markings warn other creatures that it is venomous. 

The spines on its body classify it as a stinging caterpillar. In case you happen to touch a stinging caterpillar, you will have to deal with a painful sting, skin rash, and burning sensation.

A saddleback caterpillar’s sting is one of the most painful. Members of this group have hollow, poisonous spines on their bodies that are directly connected with poison glands and can cause swelling, pain, and sometimes even fever. Saddleback stings can even be worse than wasp or bee stings. 

The southern flannel moth caterpillar can be the most dangerous to children. Due to its fluffy appearance, children find it very cute and try to touch it. These caterpillars are also known as large spines or small hair.

What Causes Caterpillars to be Poisonous?

Caterpillars can become poisonous for a number of reasons. Some of them are naturally poisonous or have stinging hairs and venomous spines, while others become poisonous due to environmental factors.

Some types of caterpillars have hollow spines, spikes and hairs. These hollow, tubular structures are directly connected with poison glands, which are located under the skin. 

The adaptation of poisonous spines is a caterpillar’s natural defence mechanism. The hollow spines function as a straw that draws poison from the poison glands and is injected into the skin of the caterpillar when it comes into contact with a threat.

Some types of caterpillars become poisonous due to the things they feed on. The North American caterpillars are not poisonous by nature but, as they feed on poisonous plant leaves, they accumulate poison inside them. 

What To Do When Sting by a Caterpillar

When stinging caterpillar rubs or is pressed against your skin, venomous spikes prick into the skin and eject toxins. This results in several physiological and skin issues. Normally, the reaction to moth caterpillar poison is mild and limited to skin, such as rashes, swelling, and burning sensations.

The severe pain caused by a moth caterpillar sting normally subsides within an hour and the rash disappears within 2- 3 days under normal conditions. However, in severe cases, it might lead to respiratory issues, rapid heart rate, nausea, and sometimes the person might even need professional medical attention.

Here are some guidelines to follow in case you or someone else around you gets stung by a caterpillar:

1. Clean and wash the affected area using mild soap and water

2. Observe keenly to see if any parts of the poisonous sting/urticating hairs are still stuck or embedded in the skin.

If so, then you should try to pull out the buck moth caterpillar hairs using a tweezer. 

Alternatively, you can put tape over the area and pull it off like a waxing strip. 

3. Apply an anti-inflammatory ointment on the affected area to treat the inflammation caused by the flannel moth bite.

You can apply isopropyl alcohol, also known as rubbing alcohol to treat the rash caused by a puss caterpillar bite.

For a painful moth caterpillar bite, you can use calamine lotion to bring relief.

Applying a baking soda slurry can neutralize the reactions from the poisons and offer relief from inflammation caused by the bite.

Some people prefer to use an ice pack wrapped in a thin handkerchief to help soothe the burning sensation and also bring down the swelling caused by the puss caterpillar bite.

In case it is a bite from a puss caterpillar and the reactions are severe, seek medical attention.

Antihistamines such as Benadryl have been shown to work in people with a severe allergy to flannel moth sting’s toxin. 

Difference Between Venomous Caterpillars and Poisonous Caterpillars

Poisonous caterpillars are those that carry around some amount of toxin inside their tissues and on the surface of their body. An example is  Monarch caterpillars. 

On the other hand, venomous caterpillars are those that produce and keep their poison in special glands. Also, they have specialized fangs, spines, or setae through which they administer their venom.

Venom and poison are both toxic substances that are developed as a defence mechanism. This is a result of evolution over the course of thousands of years. Many animals, including caterpillars, can unknowingly become poisonous during their lifespan, by feeding on toxic substances.

Nonetheless, an animal cannot be venomous due to external factors. Being venomous is an anatomical, physiological, and morphological trait. 

Picking from the examples discussed earlier on, the monarch caterpillar is an example of a poisonous caterpillar while stinging caterpillars, like a saddleback caterpillar, slug caterpillar, lo moth, buck moth caterpillar, flannel moth, stinging rose caterpillar, and giant silkworm, are categorised as venomous caterpillars.

Here are some of the poisonous caterpillars to watch out for:

1. Saddleback Caterpillar (Acharia stimulea)

A Saddleback caterpillar is about an inch long with venomous spines on each end and along the bottom of its body. It has a green ‘blanket’ around its body, with a black/purple bull’s eye in the centre. 

You can find it on a variety of plants, but mostly pear, apple, cherry, pawpaw, camellias, roses, plum, basswood and oak. Its sting is likened to that of a bee, with localized redness and swelling.

2. Southern Flannel Moth Caterpillar (Megalopyge opercularies)

Because of its appearance, children are most likely to pick it up and play with it. Also known as the puss caterpillar, woolly slug, asp, or ‘possum bug’, this caterpillar has venomous spines hidden in the hairs (setae) on its body.

When picked up, these spines can cause a powerful and painful sting. The venom can cause searing, throbbing pain, burning and sometimes a rash with red spots. 

Some people experience swelling, abdominal pain, nausea, headache, shock and respiratory distress. 

You can find them around a few species of shade trees, fruit trees, ornamental shrubs, etc. that are associated with homes, schools, and other landscaping plants.

3. Io Moth (Automeris io)

The io moth is an elegant moth with eyespots and is readily identifiable. This caterpillar majorly feeds on redbud, hackberry, willow, pear trees, and blackberry, but can be spotted anywhere when it is searching for an appropriate place to pupate.

It pupates in the ground – this is why you are likely to spot it walking around the leaf litter. 

Its sting is considerably painful, likened to a wasp or hornet sting.

4. Bag Shelter Caterpillar (Ochrogaster lunifer)

This caterpillar moves in long lines with others of its kind, bringing about the term processionary caterpillars. They are poisonous and can cause both internal and external bleeding when touched.

In some cases, the poison can cause a victim to bleed to death. You are likely to experience respiratory problems when you come into contact with even a few stray hairs from these dark brown bags. 

5. Monarch Butterfly Caterpillar (Danaus plexippus)

This caterpillar changes from a poisonous crawling bug into one of the popular butterflies in North America. It has bright strips of yellow and white arranged in partial circles around its black body. It can grow to more than 2 inches long.

Monarch butterfly caterpillar’s venom comes from all the milkweed it feeds on and is sufficient to poison or sicken predators who try to make a meal of it.

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