Deposing the Monarch

Disturbing news from central Mexico where it appears that numbers of over-wintering Monarch butterflies (Danaus plexippus) have declined this year by over 59% (http://www.guardian.co.uk/environment/2013/mar/14/mexican-monarch-butterfly-numbers?INTCMP=SRCH). This continues a decline noted over 5-6 years. These striking orange and black butterflies have larvae that feed on Milkweed (Asclepias sp) and incorporate the toxins from the plants into their tissues (hence the bright colours) as protection against potential predators. The migrations of these butterflies from Canada and North America to their over-wintering sites is one of the great animal migration spectacles. A report puts their decline largely down to the use of herbicides (farmers are not too keen on Milkweed) and logging in and around the over-wintering sites (even small changes in microclimate are said to influence numbers). It has also been suggested that spells of dry weather can kill the butterfly eggs. It would be interesting to know whether climate change could also disrupt the migration of the insects. Wind direction and strength can alter ability to cover distances. Rain isn't very helpful and the adult butterflies need to refuel on nectar.