* The new bypass could prove a lifeline for one of Britain s most threatened butterflies. * The Hertfordshire and Middlesex branch of the charity Butterfly Conservation believe the road s chalk embankments could accommodate the Small Blue butterfly, a spe

* The new bypass could prove a lifeline for one of Britain's most threatened butterflies.

* The Hertfordshire and Middlesex branch of the charity Butterfly Conservation believe the road's chalk embankments could accommodate the Small Blue butterfly, a species not seen in Hertfordshire since 2003.

* Members have successfully campaigned to have kidney vetch, the food of the Small Blue's caterpillars, grown alongside the road.

* Branch member Andrew Palmer said: "The bypass provides one of the largest areas of exposed chalk in the county. It constitutes a very significant butterfly habitat in an area where such conditions have become increasingly rare.