Royston, and in particular Therfield Heath, supports many types of butterfly which make excellent subjects for observation or photography during the (supposedly!) hot summer months when bird interest is relatively low. Therfield Heath is renowned as being one of the best sites in England for observing the Chalkhill Blue, which is on the wing in July and August. The caterpillars of Chalkhill Blue feed only on Horseshoe Vetch, which is common here. Other butterflies of the Heath include Small Copper, Common Blue, Large, Small and Essex Skippers, Brown Argus, Small Heath and Marbled White. A small colony of White Letter Hairstreak has recently been discovered on the Heath by Alan Beale, the local recorder. Good numbers of migratory butterflies such as Painted Lady and (in certain years, including 2006) Clouded Yellow can often be seen in late summer, along with the more common Peacock, Comma, Meadow Brown and Red Admiral butterflies, the last being on the wing in 2006 until late November! Below is a list of the 25 species of butterfly that I saw in the Royston area in 2006:

Small Skipper, Green-veined White, Holly Blue, Speckled Wood, Essex Skipper, Orange-tip, Red Admiral, Marbled White, Large Skipper, Small Copper, Painted Lady, Gatekeeper, Clouded Yellow, Brown Argus, Small Tortoiseshell, Meadow Brown, Brimstone, Common Blue, Peacock, Ringlet, Large White, Chalkhill Blue, Comma, Small Heath, Small White.