The usual time for Monarch butterflies to reach Dorset is when they get caught up on strong high-level wind currents as they fly down the eastern coast of USA on their way to hibernate in the Mexican highlands.
This would normally be in very late August to October and was probably the origin of the one seen by many observers in September 2012 on Portland.
This year we have already had several sightings to the east of the County. The first was seen in a garden on the Hants side of the border on the 8th and 9th July near New Milton.
Another, perhaps the same insect, was reported on the Dorset side near Highcliffe on July 13th. Later in the month, on 26th July, there was another sighting in a garden at Burton Bradstock: well to the west of Dorset.
Later still, on 1st August, two more Monarchs were reported near the Tropical Gardens at Abbotsbury.
Could these have been early migrants across the Atlantic? Or perhaps a new sort of migrant from colonies now breeding in Spain & Portugal – the 2nd sighting at Abbotsbury did fly in over the cliff from the south.
More likely these may have been releases from breeding houses and this is almost certainly the case with the Highcliffe sighting.
As well as private breeders there are many engaged in breeding from Butterfly Weddings & Funerals & escapes do occur.
The West Dorset sightings are more uncertain, and we would welcome information from anyone who knows of breeding schemes in West Dorset from which they could have been released or escaped.