I was reading one of the Facebook groups and found a picture of the Hickory Tussock Moth Caterpillar; also known as the black and white tussock moth caterpillar. Someone posted that it is very poisonous and it should not be touched? I started to wonder – how poisonous is it?
It is common for such warnings to be aggregated. I think back to the Hogweed and pictures of people in hazmat suites trying to clear it. I grew one, touched it, and no reaction at all. How dangerous is the Hickory Tussock? Will you die if you touch it? Will you get a serious rash and blistering? If there is a reaction, how common is it?
In my search for an answer, I found a lot of confusing information and realized that many people, including myself, don’t really understand the difference between a poison, a venom and an allergy. Lets have a closer look and understand how dangerous this cutie really is.
Hickory Tussock Moth Caterpillar
The hickory tussock is the caterpillar of the hickory tussock moth (Lophocampa Caryae) which lives in the eastern half of North America. Eggs are usually laid in May and June on a variety of trees including hickory, walnut, ash, elm, maple and oak. By late summer and early fall the white hairy caterpillars are fairly easy to spot against green foliage.
It is covered with white setae or hairs, and a line of black ones runs down its back. It also has four small clusters of longer black setae; two at the front and two at the back, called pencils.
It’s quite a cute caterpillar and I can see why people might want to touch it.
Is The Hickory Tussock Caterpillar Poisonous?
After checking a number of web sites, I was very confused. Some say the caterpillar is poisonous. Others say the black setae contain a venom and that this is injected into the skin. Some say the caterpillar stings – it is part of a group of so-called ‘stinging caterpillars’. And still other sites say that the rash people get is an allergic reaction.
Popular sites like news outlets and some health centers warn about how dangerous this animal is. One should never touch it for fear of serious reactions. Other sites say that most people will show no reaction.
I thought I was asking a simple question, but it turned out to be complex, mostly because people are not very careful about the words they use.
Poison vs Venom – What is the Difference?
Both are chemicals that can result in a reaction when it comes into contact with a target animal – us in this case.
The difference is in how the chemical is transferred to us. If the source is coated with it and we touch it, then it is a poison. If the source has a mechanism for injecting it or spraying it onto us, it is a venom. A bee sting and a snake bite are both venom because they are injected into our skin. If this same chemical was a slime on the outside skin of a snake, and we touched the snake, it would be a poison.
This video explains it well.
If the above video does not play try this link: https://youtu.be/KnJ4_xRfxpA
This description discusses poisons, but what exactly is a poison?
Poison vs Allergic Reaction
What is the difference between a poison and an allergic reaction.
A poison is a chemical that causes harm to our body. Dose is important, but in general, a given poison will affect all of use in the same way. For example, we will all be killed if we ingest too much arsenic.
When a chemical does not directly harm us, but instead causes our immune system to react to the chemical it is called an allergen. Allergens can also be things like dust and pollen. When the reaction is on the surface of the skin it is called allergic contact dermatitis.
When you touch poison ivy, your skin is exposed to a chemical called urushiol. In normal doses this chemical is not poisonous, but it does cause an allergic reaction in about 80% of the population. It is our immune system that causes the body to swell and get red. We should really rename this plant and call it ‘allergenic ivy’.
A key distinction between a poison and an allergen is that not everyone in a population reacts to the allergen. In contrast, everyone reacts to arsenic.
What Causes the Hickory Tussock Rash
Some of the hairs on this caterpillar have barbs, and can get stuck in your skin. They then break off, leaving small ‘little spears’ in your skin which can cause an allergic reaction.
The longer black hairs do contain a venom and when these get stuck in your skin they can inject a chemical. If these hairs break off, excess chemical can also be spread onto the surface of your skin. Both situations can cause an allergic reaction.
Is the hickory tussock moth caterpillar poisonous? No, however it is venomous.
Does the hickory tussock moth caterpillar sting? That depends on the definition of the word ‘sting’, but it does not sting in the sense of a bee attacking you and inserting a stinger into your skin. The caterpillar has no control over the movement of the hairs.
All of the symptoms described for this caterpillar are allergic reactions.
Update: October 10, 2018
After writing this article I found an article by Craig Biegler, Naturalist at Highbanks Metro Park that says, “these caterpillars have no venom or poison”. I’ve asked Craig for a reference. At this point it is not clear if the caterpillar is in fact venomous.
How Serious Are the Allergic Reactions?
This question is always hard to answer because everyone reacts differently, and anyone who has a serious allergic reaction will consider this caterpillar very dangerous. The reality is that the seriousness of reactions are much lower than reported by social or traditional media.
Jace Porter, from The Caterpillar Lab in Keene, New Hampshire, says “This particular caterpillar tends to get a bad rap. This stems from irritants on the caterpillar’s white hairs which, in rare cases, cause allergic reactions when they come in contact with human skin. Sometimes, people who touch the caterpillars develop slight redness on their skin and, less frequently, an itchy, burning rash.”
David Wagner, an entomologist at the University of Connecticut “estimates that only about one out of 100 people will experience allergic reactions. You’d have to have extremely sensitive skin,” and he’s never met anyone who’s had a reaction after touching a hickory tussock.
This study looked at three hundred and sixty-five exposures to Lophocampa caryae caterpillars (hickory tussock) that were reported to a certified regional poison information center over a 2-year period. “Pediatric exposures were responsible for 80% of the reports and 92.1% were dermal exposures, 7.5% oral, and 0.4% ocular”.
“Dermal exposures with minimal symptoms were treated at home with the supportive measures of hair and spine removal, irrigation, antihistamine, and/or topical steroid administration. Symptom resolution occurred within 24 hours. Symptomatic patients with oral exposures and positive visualization of hairs or spines, were referred to an emergency department for medical evaluation and removal of the caterpillar hairs. Removal of the defensive guard hairs or spines is the primary treatment. ”
Unfortunately this study does not give us an indication of the frequency of exposures but it is surprising that 7.5% are oral. That is probably explained by the fact that 80% of the exposures were for children. Swallowing the caterpillar can be serious for very small children.
Citizen Science at its Best
How could I resist? I had to see what an exposure does to my skin. It was easy to find one of these guys in the garden and I used the back of my hand, where the skin is more sensitive, to rub up against the caterpillar. I touched it several times and pressed fairly hard on the hairs.
Nothing happened. I did not see any hairs stuck into my skin, but they could be there. There was no immediate reaction, and no reaction over the next day or two.
Admittedly, I am not very allergic to things. I have had poison ivy in the past and maybe slight hay fever symptoms.
Statements such as “Most people who handle these creatures will experience a burning, nettle-type, itchy rash of mild to moderate severity” seem to be highly exaggerated and verge on fear mongering. One in a hundred is hardly ‘most people’!
Children are at risk. The caterpillar looks very warm and fuzzy and I can see children playing with it and even eating it, if they are very small.
There is also a risk for people that tend to have a lot of allergies. But symptoms seem to be relatively mild provided the caterpillar is not ingested.
Update: October 10, 2018
I decided to make a movie to show the reaction caused by rubbing the caterpillar. To get the right shots I did a hard rub of the caterpillar on the inside forearm. This was done twice, with each of two caterpillars – so 4 rubs all together. Under a magnifying glass the white hairs were clearly seen stuck in my arm.
There was no rash, but I did have some very mild itching. The area swelled up for 24 hours. See what happened to me in this video.
What Should You Do if You Get a Reaction
You can use a sticky tape and remove the hairs. Wash with soap and water and then apply ammonia or calamine lotion. Icing the area should reduce any swelling or itching.
If you have a more serious reaction seek medical help.
More Dangerous Caterpillars
There are some caterpillars that are more dangerous and this link provides some great pictures and information.
- Image source: The Tooth Fairy