I suspect many of you have been raised with Buddleia (Buddleia davidii, Buddleia sp) being described as the Butterfly bush. Most of us will have seen Buddleia bushes covered with all sorts of butterflies and moths. 'Ah lovely! That's so beautiful!' Only it's not. Buddleia nectar is akin to giving butterflies, and other insects, crack.

Each butterfly or moth species has specific host plants on which they lay their eggs so that the emerging larvae have the appropriate food source immediately available to eat. Take the rare Duke of Burgundy butterfly, (Hamearis lucina) for example. It lays eggs on the underside of primose flowers or the small tortoiseshell (Aglais urticae),
red admiral (Vanessa atalanta) and peacock (Aglais io) which all make use of nettles. Your nearby buddleia is drawing these away from the plants they need to thrive. Satiated with super attractive wrong nectar, the eggs of all these butterflies get laid in the wrong place. The upshot is that the butterflies don't reproduce. The eggs hatch and the larvae have nothing available to eat so they perish. Within a few years there will be no butterflies to come to your butterfly bush; the bush will have killed them. The bumblebee, bombus terrestris, is also attracted to Buddleia. Here the bumblebees feeding on Buddleia may be affected by a lack of proline, essential for flight.

The other impact of butterflies and moths being attracted to Buddleia is that the host plants these creatures usually visit have much reduced pollination. Where the usual host plant is abundant (nettles, primrose) this may not cause much damage. Some plants such as the cowslip (primula veris) rely on several solitary bee species for pollination. In return these bees thrive on the gifts of the cowslip. Add a Buddleia into the mix and both bee and cowslip are put at risk.

At Folkestone Warren site of special scientific interest (SSSI) in Kent invasive Buddleia led to the destruction of most of a specific type of chalk grassland. A whole ecosystem has been wrecked. No one planted Buddleia at Folkestone Warren; the light seeds blew there. The butterfly bush in your garden produces seeds that can cause this level of destruction.

The faunal loss can be extraordinary. One study found species count fell by 1300 per hectare per year.

It is the small, light, wind born seeds that cause the plant to spring up on abandoned brownfield sites, atop chimneys and along railway lines. Even brownfield sites have suffered ecological damage from Buddleia invasions. Defra has estimated that Buddleia control costs the British economy £961,000 annually, this is largely because it germinates easily and puts down roots in brickwork and causes damage to buildings.

Why not consider one of these shrubs that encourage the proliferation of native invertebrates that would have been stifled if you'd planted a Buddleia?
Berberis
Heathers (good for butterflies)
Dogwood
Hebes
Lavender (good for butterflies)
Mahonia
Currants (Rubus)
Thyme
Viburnums

Bibliography
Defra et al. (2008). The Invasive Non-Native Species Framework Strategy for Great Britain. Defra,
London.
Plantlife (2012) Invasives and the law.
www.plantlife.org.uk/uploads/documents/Invasives_and_the_law.pdf.
Shardlow, M. (2010). Buddleia and invertebrates. Letter to British Wildlife 21, p 301.
Williams,F. et al (2010). The Economic Cost of Invasive Non-Native Species on Great Britain. www.CABI.org
The Invasive Buddleja davidii (Butterfly Bush)
September 2009 The Botanical Review 75(3):292-325
DOI:10.1007/s12229-009-9033-0