Fleam Dyke trip

29th July 2023 - eight NatureWatch members joined the trip to walk along the stretch of Fleam Dyke between the Bedford Gap and the A11.  The aim was to see Chalk Hill Blue butterflies, and to see whether this summer they were as prolific as normal.  Fleam Dyke is linear chalk soil site, good for a number of specialist chalkland plants, including Horseshoe Vetch, this being particularly important as the foodplant for Chalk Hill Blue butterflies. Other rare chalkland specific plants were also present, including Dwarf Thistle (aka Ground Thistle), Squinancy Wort and Clustered Bellflower.

During the walk, an impressive 18 species of butterfly were seen on the walk to and on the dyke, with Chalk Hill Blue and Gatekeeper being the most prolific. As it was a little breezy, many of the butterflies were staying closer to the ground sheltering amongst the plants, but when the wind occasionally eased, a host of Chalk Hill Blue suddenly appeared in their usual profusion. 

A Brown Hawker was seen flitting skillfully through the grass stems, and a Hobby was also seen, passing low over the crop in the field alongside the dyke.

Male Chalk Hill Blue

Female Chalk Hill Blue - darker brown underside with checkered wing fringe, 

and lacking the strong orange colouration of the Brown Argus

Male Chalk Hill Blue

Mating pair of Chalk Hill Blues ...

... with a second male trying his luck!

Another mating pair of Chalk Hill Blue

Male Chalk Hill Blue

Female Brown Argus - distinguished by brighter markings, and 

the two spots close together (or 'twin spot') on the lower hindwing 

Female Brown Argus

Holly Blue - pale blue underside, with several black spots

Gatekeeper - double eyespot, and line of white dots 

on the lower hindwing

Gatekeeper

Painted Lady

Peacock

Small Tortoiseshell - a somewhat tatty specimen!

Comma

Brimstone

Small White

Large White

Green-veined White

Speckled Wood

Large Skipper

Essex / Small Skipper (exact id unclear)

Brown Hawker

General view of dyke

Greater Knapweed, Wild Parsnip, Spiny Plumeless Thistle

Dwarf Thistle or Ground Thistle

Dwarf Thistle or Ground Thistle

Squinancy Wort

Clustered Bellflower

Tufted Vetch or Cow Vetch

Restharrow

Common Toadflax

Ploughman's Spikenard

Fireweed

Brown Knapweed (white flower - an alien to the UK)

and Greater Knapweed and Clustered Bellflower

RiverCare - river sampling results

27th July 2023 - the RiverCare team meet to undertake the monthly river sampling of the river Granta, by the ford. They found several Signal Crayfish and four small fish, including two Bullhead (aka Miller's Thumb) and what are possibly two Stone Loach. If so, the latter only live in very clean water, not tolerating even mildly polluted water, so that's good news.

Also good numbers of the larvae of both Blue-winged Olive and Olive (both types of Upwing flies) and those of Mayfly and Cranefly. Several Cased Caddisfly and Freshwater Shrimp were also found, as well as a Water Boatman.

Bullhead aka Miller's Thumb

Stone Loach (and small Olive larva)

Stone Loach, showing three pairs of barbels around the mouth

(and a Mayfly larva underneath)

Signal Crayfish

Signal Crayfish

Mayfly larva

Mayfly larvae

Mayfly larvae

Blue-winged Olive larvae

(note the wider 'skirt' around the gills towards the rear of the body)

Blue-winged Olive larva

Olive larva (lacking the wider 'skirt')

Olive larva

Water Boatman

Cased Caddisfly larva

Freshwater Shrimp, Gammarus

Pea Clam, or Fingernail Clam - note the extending foot

River Worm (left), and Cranefly larvae