Nature features

Magdalen Hill Down near Winchester is the perfect habitat for the Chalkhill Blue butterfly - numbers have grown from 400 in 1990 to 3,236 in 2006.

The butterfly-friendly landscape

The land was dominated by scrub when Butterfly Conservation acquired the site in 1989. 

The charity immediately began work to open up areas where grassland flowers could survive.  They brought in animals to graze the site which also helped the flowers to return and keep the grass short - which the Chalkhill Blues prefer.

Battle

But grazing animals aren't enough - it needs lots of human effort to keep the 46 hectares site in good condition for butterflies.

Encouraging a butterfly-friendly environment

Throughout the year the site's warden, Patrick Fleet battles the vegetation - cutting back the tough invasive plants like brambles and wild clematis which the grazing animals can't get through. 

The more delicate grassland plants then get a fighting chance - and if they are thriving, the butterflies flourish.

Despite the name, it is only the males that are the beautiful blue colour - the females are a rich brown.  Mid-summer is the peak flying time when the males go searching for a mate.

A sure-fire way of attracting the Chalkhill Blues is a simple bate of horse manure - the moisture and minerals in dung is thought to make it particularly attractive.  In fact, in 2006 the team once recorded 18 Chalkhill Blues on a single dog poo.

Ant music

The females only lay on horseshoe vetch - the sole foodplant of the caterpillar. The egg will overwinter, then in the spring the caterpillar will hatch out.

Ants and caterpillar

Like the Adonis Blue, the Chalkhill Blue caterpillar has a remarkable relationship with ants.

The ants feed on a sugary substance excreted from the caterpillar and, in return, they ward off predators. Remarkably, both the caterpillar and the pupae have been recorded 'singing' to the ants.

As for the future of the Chalkhill Blue - according to Lynn Fominson from Butterfly Conservation - it's down to preserving and joining up existing wildlife havens in among areas of farmland: 

"The problem is that boring monoculture feeds people and provides good money for farmers.  So until someone is prepared to really compensate farmers for the loss of land for growing crops on, that's not going to happen."

Inside Out - Wednesday's - 7.30 BBC1