Black Widows Part 1: The Chemistry of Venom

So here’s what my kids found in the garage- a Black Widow, Latrodectus hesperus.

Tangent: It should be noted that this is- yes- another great wildlife photo, even if it is in my garage, and therefore another positive step forward in my continuing journey of redemption as a wildlife photographer.

6 years ago, when we moved into our house, the previous owners left only 1 thing behind- a small pile of bricks in the garage. I assume they left it; for all I know the previous owners left it for them. Who knows, maybe it pre-dates the house? Maybe the pile of bricks was left by the first Mormon pioneers, or even the Donner party as they struggled to lighten their load.

Tangent: The Donner party almost certainly passed within 100 yards of our house.

In any event, the Black Widow, a female, was sitting in her web spun between the brick pile and the garage wall, And when I tried to dispatch her, she scurried into the bricks of the ancient, timeless brick-pile.

There are so many fascinating aspects of the Black Widow, but I’ll focus on just 2 of them before getting to the main point of this 2-part post: chemistry (today) and lust (tomorrow).

There are 31 species of Latrodectus in the world, spread across every continent except Antarctica. 4 of those 31 are native to North America, and 3 of those are “Black Widows”. The Western Black Widow, most common in Utah, is Latrodectus Hesperus.

Everybody knows that Black Widow venom is dangerous. What most don’t know, and biologists are still unraveling, is how phenomenally complex it is. Black Widow venom is 15 times more potent than Rattlesnake venom, but rarely kills adult humans, because the amount injected is so minute. (The venom does an excellent job of sickening predators who consume it, who presumably then remember the bad meal and its distinctive red hourglass marking, avoiding it in the future.)

There are a whole slew of active ingredients in Black Widow venom; you could probably structure an entire organic chemistry class around the chemical composition of it. But the most important and distinctive active ingredients are a series toxins called latrotoxins. Latrotoxins are monster-sized molecules with dozens of different atoms (atomic weight > 120kDa) and exactly how all of them work is not yet completely understood. Black Widow venom contains at least 7 different latrotoxins: 5 that work specifically on invertebrates (ie. Bugs), 1- called alpha-latrotoxin, and which is the best-studied and understood- that works specifically on verterbrates (i.e. us). Alpha-latroxin is tetramer, a type of big-ass protein molecule consisting of 4 distinct pieces. The 7^th and final latrotoxin works specifically on crustaceans.

Tangent: This last one is particularly interesting. There’s only 1 genus of land-based crustacean in the world: Armadillium, which we know as Woodlice or Potato Bugs. Evidently these critters have been an important enough food source (since no Woodlouse could conceivably be a predator to Latrodectus) to support the evolution of the crustacean-specific latrotoxin. And in fact, when I swept out behind the brick-pile, I swept up dozens and dozens of dried-out woodlice carcasses…

We’ve visited lots of great organic chemistry examples already this Spring: Monarch butterflies, the Black-headed Grosbeak, Low Larkspur, Snowflies, Poison Ivy and Wild Iris, allelopathy in Dyers Woad and even reverse-allelopathy in Musk Thistle, but Black Widow venom seems the most complex, sophisticated and finely-tuned of any we’ve looked at to date. And that’s probably been one of the biggest surprises for me of writing this blog- how fascinating and elegant the chemistry of living things is. In high school and college I suffered through Chemistry classes bored out of my mind. If they’d explained to me how amazing and important chemistry is in the real, living world, I would have been a lot more interested.