Worcestershire Record No. 17 November 2004 p. 40-42

Terry Knight

In Worcestershire there are currently about 18 transects that are walked once a week through the summer to record numbers of butterflies (Gregory 2003). Few of these are located in areas that are typical of normal Worcestershire countryside. Instead they have been purposely set up at sites where butterfly numbers are expected to be high and/or rarer species exist. One of these transects is at Windmill Hill, Middle Littleton. This is a Site of Special Scientific Interest and a nature reserve which is noted for its invertebrates.

As far as is known, there are no bumblebee transects elsewhere in the county.

As these special butterfly sites make up just a few percent of the area of the county most of the transects cannot give an indication of the numbers of butterflies in the countryside as a whole. At the end of February 2001 the Foot and Mouth outbreak started to close off the countryside and it looked as if no butterfly transect recording would be possible that year. This provided the spur to find an "on-road" transect location that would be as typical as possible of the present Vale of Evesham in order to give some indication of the numbers in the wider countryside.

Bumblebees

It was expected from the outset that butterfly numbers would be less than at Windmill Hill and so it would be practical to record bumblebees at the same time. No attempt would be made to identify species of either Bombus or Psithyrus but it is likely that these include B. lucorum, B. terrestris, B. pratorum, B. lapidarius, B. hortorum, B. pascuorum and P. vestalis. The narrow strip of road verge has some Meadow Cranesbill, Creeping Thistle, Spear Thistle, Common Mallow and Autumn Hawkbit which attract bumblebees and consequently the number recorded is probably somewhat greater than if the road verge was absent.

The standard method of butterfly transect recording was used with an adaptation to suit the site. This consisted of recording for a distance of five metres on one side of the walk rather that two and a half metres each side. Consequently, in general the transect covered about one metre of road verge plus four metres of field beyond. On the eastward part of the walk the area south of the road was recorded and on the westward part the area north of the road.

Week 1 is from April 1st to April 6th and week 26 from September 23rd to September 29th.

The impression gained during recording was that the derelict orchard and its immediate surroundings harboured a greater density of butterflies than the rest of the transect. Consequently, as well as comparisons being made using the full transect data, they are also made using data from sections near the orchard (sections 2, 3, 8 and 9) and sections away from the orchard (sections 1, 4, 5, 6, 7, 10 and 11).

It transpired during 2001 that permission was granted to continue the Windmill Hill transect through the Foot and Mouth crisis. This made it possible to use the results from that butterfly transect as a basis for comparisons at Blackminster thus eliminating most of the effects of variations in the weather.

A summary of the Blackminster results is given in Tables 2, 3 and 4. The total number of each species of butterfly recorded over the four years is given in Table 5. The most abundant species are Small White, Meadow Brown, Gatekeeper, Green-veined White, and Small Tortoiseshell. Graphs showing the butterflies and bumblebees over the 26 week period each year as a percentage of the Windmill Hill butterflies are given in Figures 1, 2 and 3. The graph shown in Figure 4 gives the average number of butterflies and bumblebees per walk over the 26 weeks.

The average number of butterflies and bumblebees seen per walk at Blackminster over the 4 year, 26 week period works out as 3.71 per kilometre and 2.85 per kilometre respectively. This compares with 44.83 per kilometre for butterflies at Windmill Hill and gives a ratio for Blackminster butterflies of 8.3 percent and bumblebees of 6.4 percent.

It appears that the derelict orchard has little or no effect on the distribution of bumblebee sightings. However, this is not the case with the distribution of butterflies. In each of the four years the density of butterflies near the orchard has been greater than away from it. The reason for this seems to be that about 90 percent of Gatekeepers and 80 percent of Meadow Browns were recorded in sections near the orchard and the grassland opposite it.

As expected, in typical Vale of Evesham countryside the number of butterflies is much less than on nearby natural grassland managed for nature conservation. This short term study appears to show that there may be less than one tenth in typical present day countryside. At Blackminster the number of bumblebees seems to be generally slightly less than butterflies.

GREGORY NEIL 2003. VC 37 (Worcestershire) Butterfly Transects Annual Review 2002, Worcestershire Record 14 : 20.