Figure 1 Changes over time in the proportion of the illustrated melanic and non-melanic morphs of the two-spot ladybird beetle along a transect of ca. 115 km in length in the Netherlands (bottom-left). Samples were collected in each of the 5 years indicated at 16 more or less evenly spaced localities from west to east. Colouring of years matches the histograms for melanic frequency in the individual samples from each locality. The panel on the bottom-right shows deviations in average temperature from a ‘normal’ season/year at De Bilt (red spot on map). From left to right, columns represent data for winter (Wi), spring (Sp), summer (Su), autumn (Au) and the overall year (Tot), respectively, and from top to bottom for different years beginning before the period of ladybird sampling. The colour of each block indicates the extent to which the average temperature in the particular season/year deviated from ‘normal’; white, no deviation, blue, cooler than normal (dark blue more extreme than light blue), red, warmer than normal (dark red more extreme than light red)(from Brakefield & de Jong, 2011)
The story has a second dark aspect. The researchers had trouble reaching acceptable sample sizes in the 2004 sampling season. They even failed to find 2 spot ladybirds in two localities where they previously had been abundant. They attribute the decrease in numbers of the 2 spot ladybird to the impact of the invasive harlequin ladybird, which reached Holland in 2002. Not only the melanism cline is gone, but the 2 spot seems to be dissapearing as well.
Brakefield PM, & de Jong PW (2011). A steep cline in ladybird melanism has decayed over 25 years: a genetic response to climate change? Heredity PMID: 21792220
So it seems I do have melanic 2 spots in the garden (above). Thank you to Helen Roy, who curates the Ladybird survey site for the ID.