These flowering plants are a beautiful sight. They cover valleys with a sprinkling of yellow, a picture-perfect postcard of a peaceful meadow.

The plant is called Rhinanthus minor but it is more commonly known as cockscomb or little yellow rattle. It is common in grasslands around the world.

It is actually a parasite that feeds off neighbouring plants.

The more they take from their victims, the more successful they become. They are vampire plants.

They attach themselves to the roots of neighbouring plants and suck out their nutrients.

R. minor belongs to a family of "hemiparasites", "hemi" meaning "half". These plants get their name because, while they can steal food from other plants, they can also produce their own food through photosynthesis like most plants.

However, without parasitising another plant R. minor cannot grow to its full height.

"If it can't attach to anything, if it grows in a sad little pot on its own, it never becomes more than a few centimetres high," says Libby John of the University of Lincoln in the UK.

John and her colleagues have now looked into the impact this plant has on the life around it. "We suspected they might have more impacts on other species such as invertebrates," says John.

The team manipulated small plots of land in a meadow in the south of England.

They compared plots of land in which the parasitic plant had either been removed, kept the same or doubled in density. There were 13 plots of each kind.

As expected, the total mass of plants was reduced in the places where the vampire plant was most abundant. But while there were less plants, the diversity of the species that grew near R. minor actually increased.

That's because the parasites' main victims are grasses. When grass is suppressed in this way it allows other plants to flourish.

More surprisingly, the researchers discovered that invertebrates also increased in number, as did their predators. 

They are "Robin Hood plants"

"We saw double the numbers of invertebrate animals in the community," says John. "It wasn't just things which feed on plants, it went right up to the predators of these herbivores."

These included caterpillars, beatles, snails, woodlice, wasps and spiders. The study, published in the journal Ecology, shows for the first time that vampire plants have a positive impact further up the food chain.

You can think of these plants in two ways, says John. In one sense, they are vampires that suck others dry. But they are also "Robin Hood plants". They feed from the dominant grasses, thereby providing space and resources for other species.

Quite why there was such a dramatic increase in the diversity and abundance of plant and animal communities is not quite clear.

It could be due to a change in microclimate. By reducing grass coverage, the parasite could let in more warming sunlight.

Alternatively, maybe the extra wild flowers are more attractive than grasses to the plant-eaters that come to feed there. They could simply be tastier, says John.

The finding could help the conservation and management of chalk grassland communities, says lead author Sue Hartley of the University of York, UK. Such areas "are exceptionally species-rich but also rare and threatened."

"None of us predicted there would be such dramatic and positive impacts on other components of the grassland community," says Hartley.