It's bad enough when a parasite latches on to your body to suck you dry. But when it starts eavesdropping on your communications, enough already.

That's what the parasitic dodder vine does. It consumes water and nutrients from a host plant and, scientists have just discovered, it taps into the host's communication system.

Plants use RNA molecules to send messages to different parts, say from roots to leaves. In the new study, RNA molecules from a host tomato plant were found in the parasitic dodder vine, up to a foot away (30 cm) from where the dodder grafted itself to the host.

Picking up these RNA messengers could help the parasite synchronize its lifecycle with that of the host plant, explained Neelima Sinha at the University of California, Davis. "It might be important for the parasite to know when the host is flowering, so it can flower at the same time," before the host dies, she said.

The research, funded by the Rockefeller Foundation and detailed online in the journal New Phytology, could lead to new ways to combat parasites that attack crop plants.

The discovery is yet one more surprising method of communication involving planets.

In a 2006 study, baby dodder plants were found to sniff the air for signs of plant victims, then attack.

Similarly, a western U.S. shrub called sagebrush has a remarkable ability to chat. When one is damaged by insects, it broadcasts the predator's presence by releasing odors into the air. Other sagebrush pick up on the smells from their wounded brethren and get their defenses going.

Earlier this year, a research team found that insects below and above the ground use the mustard plant like a chemical telephone. A bug munching on the roots, for example, could send chemical signals up to the leaves to essentially put out a "no vacancy" sign.

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