The Plant They Never Eat

The caterpillars had been eating clover for two weeks, so Maya noticed the second one dragged a different leaf into its corner of the jar.

"That's not clover," she said.

Soren leaned in. "It's not eating it, either."

They watched. The fat green caterpillar had spun a loose net of silk in the corner of the jar, and now it was hauling shreds of a fuzzy gray leaf into the net, patting them down, weaving them in.

"It's building the cocoon out of it," Maya said. "But it never ate that plant. It ate clover the whole time."

"Maybe it just grabbed whatever was nearby."

"There's nothing nearby. We only gave it clover." Maya tipped the jar. "Where did it even get that leaf?"

Soren checked his notebook. Two days ago he had emptied a handful of yard weeds into the jar because Gran said caterpillars liked variety. Most of it had gone brown and untouched.

"I dumped some stuff in," he said. "It didn't touch any of it. Not one bite. But it kept that one."

"Kept it for what?"

Gran was on the porch shelling peas and only half listening. "That's mugwort," she called, when Maya held the fuzzy leaf up to the screen. "Grows all along the fence. Bitter as anything. Nothing eats it."

"This caterpillar doesn't eat it either," Maya said. "It's sleeping in it."

Gran shrugged. "Then it's got better taste in bedding than in food." She went back to her peas.

Maya sat down on the grass with the jar in her lap. "So it walked past its actual food, found the one bitter plant nothing touches, and carried it back to build a bed out of it."

"Right before turning into a moth," Soren said. "It's about to seal itself in. It's spending its last effort on a plant it'll never use once it's a moth. Moths don't even have the same mouth."

"Then it's not for the moth."

They looked at each other.

"It's for something inside the cocoon," Maya said slowly. "But there's nothing inside the cocoon except the caterpillar."

Soren tapped his pen against his teeth. "Not yet."

That was the sentence that stuck. Not yet.

"What gets inside a cocoon?" Maya asked.

"Wasps do." Soren had read this somewhere and it came up now like a stone turning over. "Parasitic ones. They lay eggs on caterpillars, and the wasp babies eat their way out. That's a whole thing. It happens to loads of caterpillars."

"So maybe the wasp already got this one."

"Maybe. But look." He pointed. The caterpillar was still working, calm, methodical, tucking the bitter gray leaves into the walls of its shelter. "If a wasp was already eating it from the inside, would it be building this carefully?"

"Maybe it doesn't know."

"Then how does it know to grab the mugwort?"

Maya went quiet. She turned the jar slowly so the little cocoon-in-progress came round to face her.

"Okay," she said. "Try this. What if it doesn't know a wasp got it. What if it grabs the mugwort every single time, no matter what. Just in case."

"In case of what?"

"In case a wasp comes later. When it's sealed in and can't do anything about it." She pressed her thumbnail into the grass. "It can't fight the wasp once it's a cocoon. It just lies there. So it can't wait to find out if there's a wasp. It has to decide before."

Soren stopped tapping his pen.

"The mugwort's bitter," he said. "Nothing eats it. Gran said. What if that's the point. What if it's poison to the wasp babies but not to the moth."

"So the caterpillar builds a wall of the one thing that kills whatever might try to grow inside it."

"Before anything's tried." Soren was writing now, fast, the pen digging. "It gathers the medicine before it's sick. It can't know if it's sick. It just, it just always brings the medicine."

Maya was staring at the caterpillar like it had said something out loud.

"That's the part," she said. "That's the part that's wild. It's not reacting to anything. Nothing bit it that we saw. It's not scared. It's just doing the thing every time, forever, all the way back through every caterpillar that ever did it, because the ones that didn't grab the mugwort, their cocoons filled up with wasps and they never became moths."

"So the ones that walked past the mugwort aren't here," Soren said.

"They're not anywhere. Only the mugwort-grabbers had babies. And their babies grabbed mugwort. And here's this one in a jar in your gran's yard still doing it." Maya laughed, a little shaky. "It's carrying a plan it never made. It doesn't know it's a plan."

Soren set the pen down. "How many things do that?"

"What do you mean?"

"Carry a plan they never made." He looked out at the fence, the whole tangle of green along it, the mugwort somewhere in there that nothing ate. "Everything out there. Every one of them is doing some old thing for a reason that got decided a million caterpillars ago and none of them know it. The whole yard is full of it."

Maya followed his eyes to the fence, then to the flower beds, then to the peas Gran was shelling on the porch, then, without meaning to, down at her own hands.

"Us too," she said.

Neither of them said anything to that.

The caterpillar patted the last shred of gray leaf into the wall. It fitted it, checked it, tucked its body in behind it. The silk began to thicken over the gap until the bitter leaves were sealed inside with the caterpillar, medicine and patient and doctor all shut in together to wait for a wasp that might come and might not, that the caterpillar would never see and never needed to see.

Gran came down off the porch, drying her hands. "Sealing up, is it?"

"It packed itself in poison," Maya said. "On purpose. Sort of."

Gran peered at the jar. "Huh," she said, and meant it more than she expected to. "Clever little thing."

"It's not," Soren said. "That's the clever part."

Inside the jar the last thread of silk closed over the fuzzy gray wall, and the caterpillar went still, and along the whole fence line the mugwort nobody ate went on standing in the evening light, bitter, ready, waiting to be needed by something that hadn't hatched yet.