Thread by @BugQuestions

For this week's #DeepDive, let's talk about the Southern Flannel Moth!

It's not well known, although we get lots of pictures of these guys.

Severe outbreaks can cause schools to be cancelled, so this is a very weird and important venomous caterpillar.

flic.kr/p/21bvzep

I am aware of three major outbreaks of these guys, although I'm certain there are others which have escaped my attention.

All three happened in Texas, one in 1913 and 1920 closed schools until the caterpillars could be sprayed. A third, in 1958 resulted in thousands of stings.

These guys like to feed in elm and oak trees, popular landscaping plants, and will fall off when disturbed by a bird or a parasitic wasp.

Most encounters happen when they land on someone (like inside a shirt) or while they're looking for places to pupate.

Unlike spiders, flannel moth (asp, Trump Hair, etc) caterpillar stings can be easily recognized by the gridlike pattern of their stings.

Under that crazy hairdo, they have regularly spaced stingers that break off and let venom leak into the skin.

So...why would a caterpillar need to be venomous?

It's all about protection. If something tries to grab them, they can deliver a quick and extremely painful sting...allowing them time to drop off the plant and hide 20 ft down.

(Note: Not a Flannel Moth Caterpillar)

The picture above isn't a flannel moth caterpillar...instead, it's a Saddleback caterpillar which is another venomous species.

Unfortunately, I don't have any great action shots of Flannel Moth caterpillars stinging and this species is better because the stingers aren't obscured

In general, venom in caterpillars is pretty rare. There's only about 30 species in 10 families that are venomous. However, they're spread pretty far and wide.

Their venom isn't very well researched, either.

Megalopyge venom is pretty much unknown. We *think* it's a protein which chews up other proteins, but it's pretty much uncharacterized.

If you think about it, that's crazy. There's a caterpillar which can be an epidemic, and we don't know how it makes people sick!

While we don't know a lot about the venom of the Southern Flannel moth, we know a lot more about the venom of the caterpillar below.

See...flannel moth venom is very painful.

The caterpillar below is Lonomia obliqua...and it's famous because it's venom can kill people.

Lonomia venom isn't particularly toxic (it's about 1/10x less toxic than black widow venom), and deaths are somewhat rare (2.5% of stings).

However when stings are bad, they're *really bad*.

The venom of Lonomia is actually very interesting. Two species can cause fatalities, and the venom of each species acts in very different ways.

The venom of both lethal species acts on the blood clotting cascade, and throws it out of whack.

Death is caused by brain bleeds.

While we can't go through *every* venom protein here on Twitter, we can discuss the main component.

The main component of Lonomia venom is called Lopap, and it acts like a switch that flips on the enzyme which forms the actual blood clots.

So...now, here's the weird thing. People stung by this caterpillar don't die from strokes.

They die from *bleeding*

...but this protein causes blood to clot.

Why would it cause bleeding?

Again, we can only give a simplified version here...due to the complexity of the clotting cascade and the interaction of the different venom components.

However it seems that Lopap is so efficient that it depletes the supply of Fibrinogen...which eventually causes massive bleeds

So...this seems like it would have some medicinal properties, if the effects could be controlled and localized.

However, *a lot* more research needs to be done before it gets to that point.

So...all in all, there are venomous caterpillars which have outbreaks that can cause disruption in people's every day lives. In South America, there are even caterpillars which can kill people.

Despite their medical and cultural significance...we know nearly nothing about them!

Side note 1: If you want to read up more on Lonomia venom, here's a very thorough (but not very accessible) review:

Carrijo-Carvalho, L. C., & Chudzinski-Tavassi, A. M. (2007). The venom of the Lonomia caterpillar: an overview. Toxicon, 49(6), 741-757.
bit.ly/2HCIkEr

Side note 2: If you want to see what the adults look like or if they're found in your area, you can find that information at the @BugGuidenet link below:

bugguide.net/node/view/4475

Side note 3: @kmagnacca was super awesome and reminded me of a paper I read, but opted not to cite because it covered the death of someone stung by Lonomia...and it has pictures.

However, that paper (cited below) also has a figure which shows the other Lonomia venom proteins!