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Lots of plants make nectar to attract pollinators, but some make special, extra nectar pots outside their flowers to feed their bodyguards.

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Michael: Plants are a lot like animals, at least in the sense that they have to get nutrients to grow, fight off anything that wants to eat them, and reproduce. But, unlike most animals you may have noticed plants can't just get up and move around, which is why some of them put out nectar to recruit bodyguards.

Lots of flowering plants produce sugary nectar which attracts pollinators like birds, bats, and insects, they take the pollen with them to the next flower, helping the plants reproduce, but a few plants have evolved a completely separate source of nectar. They're known as extrafloral nectaries, special structures outside the flower that produce a liquid cocktail of sugars and amino acids, a lot like the nectar inside flowers just in a more strategic place. And as nectar-eaters defend their source of food, the plant ends up with body guards. Nectaries, both the floral and extrafloral kind, are meant to attract and reward animals, creating what's called a mutualistic relationship. The animals benefit from the nectar since they get food and the plant gets either pollinators or protection, it's a win-win.

For instance, in Inga plants in tropical rainforests, ants will get rid of other plant eating insects. These outside nectaries are rich in carbohydrates like sucrose and glucose as well as proteins and amino acids, all important nutrients for the ants. In exchange for food, the ants protect the plants from invaders like caterpillars.

They're pretty good at it, too. Studies show that leaves without ants get much more damaged than leaves that do have ants, and when a plant eater comes to munch on its leaves, the Inga can make extra nectar as a bonus incentive for the ants. The plant is basically saying "come help, I'm under attack, take more sugar!"

Then there's the passion flower, a North American plant that has extrafloral nectaries at the base of each leaf and under the flower bud. The passion flower already has poisonous chemicals in its leaves, but some species of butterfly evolved an immunity to the toxic leaves, and recruiting ants gives the flower another line of defense. In the 1980s, a group of researchers removed the outside sources of nectar from some passion flowers. They found that those plants had fewer ants around them, were attacked more, and made less fruit.

Even cotton plants have them, thought they aren't looking for ants, they're trying to attract parasitic wasps. These wasps are a lot different from the yellow jackets invading your summer picnic. For one thing, they're tiny, they also happen to lay their eggs inside caterpillars. The eggs hatch into larvae while they're still in the Caterpillar and start to eat it, eventually clawing their way out through its skin, all while it's still alive. Then they take over the Caterpillar's mind, forcing it to protect them as they keep growing. Once they fly away, the Caterpillar starves to death. As you can probably imagine, it's an effective way to kill caterpillars, which is why some farmer's use these wasps as a natural pesticide. The cotton plant sets out its nectar as a food source for the mini wasps and in return for the sugary snack, the parasitic wasps stick around and take over the caterpillars.

But nectar's good for more than just defending against insects, according to a study published in 2009 in the Plant Journal, it also has compounds that protect the plant from invading viruses, bacteria, and fungi. For example, the nectar of certain acacia plants contains proteins called chitinases that stop invading fungi, meaning that sometimes the extrafloral nectar itself is a kind of body guard. That nectar doesn't come cheap though, energy-wise. To make it, the plant has to use energy it would otherwise be using for things like growth and reproduction, but for a lot of plants, it's worth setting out a little nectar pot for a little added security.

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