In the UK Half of the butterflies are under threat of extinction, and more than 70% are in decline, we can help turn this process around by planting more Buddleia and more importantly different varieties of Buddleia.  Buddleia is called the "Butterfly Bush" for a very good reason, it acts like a magnet to butterflies, they just love Buddleia nectar.  If you are wondering why butterflies like particular varieties of Buddleia here is an interesting snippet from
Clemson University in South Carolina USA .....

 

 

"visitation rates were low on those having white or pale lavender flowers and greatest on those having red, pink, or lavender-pink flowers. This is probably due to the fact that butterflies, unlike many insects, can perceive red wavelength colors." 

 

So before you buy another davidii, consider planting another variety of Buddleia to encourage different species of butterfly  The more variety and colour the better! (there are plenty to choose from)

 

Butterflies love Buddleia because of the nectar, and nectar is the butterflies primary food source that gives them the energy to survive and reproduce.  Butterflies that are most attracted to Buddleia are:

 

Brimstone (Gonepteryx rhamni)
Comma (Polygonia c-album)
Common Blue (Polyommatus icarus)
Gatekeeper (Pyronia tithonus)
Green-veined White (Pieris napi)
Holly Blue (Celastrina argiolus)
Large Skipper (Ochlodes sylvanus)
Large White (Pieris rapae)
Meadow Brown (Maniola jurtina)
Painted Lady (Vanessa cardui)
Peacock (Inachis io)
Red Admiral (Vanessa atalanta)
Small Copper (Lycaena phlaeas)
Small Heath (Coenonympha pamphilus)
Small Skipper (Thymelicus sylvestris)
Small Tortoiseshell (Aglais urticae)
Small White (Pieris rapae)
Speckled Wood (Pararge aegeria)
Wall Brown (Lasiommata megera)

 

They love Buddleia because it produces nectar that has a higher content of sucrose, glucose, and fructose than many other garden flowers, in particular Buddleia generally has a higher sucrose level (two or three times higher than fructose or glucose) and that is what attracts butterflies, however Buddleia do not produce much nectar, which is why we see butterflies spending so much time on a particular plant. It is also worth mentioning that usually only the larger butterflies visit Buddleia, this is because the tiny individual flowers of Buddleia are relatively long and the smaller butterflies simply can't reach their proboscis far enough into the flower to extract the sucrose laden nectar.