Two years ago, Time Out New York asked me to write a set of instructions on how to murder a dinner guest. It was one of the most thrilling writing assignments I'd ever been given. I unleashed my inner P.D. James and created the most foolproof scenario I could imagine—monkshood in the soup: it grows almost everywhere and looks enough like parsley that one could claim it was a tragic accident.

Since then, I have spent a great deal of time thinking about the perfect murder. The problem is most people don't want to talk to me about how to pull off a flawless homicide. It's a real conversation-ender; dinner guests tend to put down their forks and remark on the lateness of the hour, and even my husband gets a little nervous when the subject of untraceable poisons comes up.

So imagine my excitement when the Tucson Festival of Books asked me to teach a workshop for mystery writers on how to kill a character using "natural" means. At last, a group of people who not only enjoy talking about the methods of murderers but are required to do so as a condition of their employment.

I showed up with my ever-growing list of tips for criminals. The room was packed; a moderator stood at the door and turned people away for the entire hour. Anyone lingering in the hallway might have wondered what all the laughter was about, but mystery writers all seem to have a delightfully devious sense of humor. My darkest, most sinister jokes got roars of appreciation.

My garden club audiences enjoy a few tales of murderous wives dispatching their husbands with oleander soup, but for the most part, they expect me to caution against the use of these plants. Wear gloves in the garden, I tell them. Keep small children away from the daphne berries. Keep dogs away from the sago palm.

But with this group, I was dispensing advice, rather than warnings. "I like the suicide tree for domestic murders," I told them. "The nuts are quite tasteless, so you can work them into a curry or a pudding with no problem." The mystery writers jotted this down the way you'd make note of a recipe.

"Now, for assassinations, ricin is very nice, but it's been done before," I said. "You might think about ratbane instead. Ranchers use it to poison livestock predators, so that's good for a western."

Then there were the false clues—the MacGyvers. "I've got a whole list of plants that explode, scattering their seed so loudly it sounds like a gunshot. That could send a detective down the wrong path for days. Could anybody use something like that?" Several hands went up. "How about a plant that smells like a rotting corpse?" Oh, yes, those could come in handy too, they told me.

Then there are the caterpillars whose sting can shut down the liver before the antivenin can be flown in from Brazil. The tarantula's venom sac tucked into a blackberry pie. And my favorite: the death-watch beetle, which lives in the rafters of old houses and knocks against the wood, calling to its mate. Edgar Allan Poe's murderer in "The Tell-Tale Heart" sat awake at night, "hearkening to the death watches in the wall." The sound, I told my audience, was supposed to foretell the death of someone in the house. Oh, yes, they murmured, they could definitely employ a death-watch beetle.

And the questions—oh, the questions this audience had. No queries on pruning or transplanting from this crowd.

"Would hemlock show up in a standard autopsy?" asked one writer.

"Rather than use a bug pit to kill someone, as you suggest," asked another, "could I use it to dispose of the body?"

And my favorite: "If I paralyzed my victim with coyotillo berries and then ran them off a cliff, would the usual sort of rigor mortis set in?"

I was so happy I could hardly answer. I just stood grinning foolishly at my brilliant students, these criminal masterminds, my newfound comrades and accomplices. And I have never felt more at home.

Amy Stewart is the New York Times bestselling author of Wicked Bugs: The Louse That Conquered Napoleon's Army and Other Diabolical Insects and Wicked Plants: The Weed That Killed Lincoln's Mother and Other Botanical Atrocities. She is available to speak to mystery writers any time, anywhere. Find out more at