Site feature providing a more detailed description, photos and other information for the butterfly observer.
Photo 1 - View Along The Switchback From The Car Park
Large mixed woodland on Hants/Wilts border.
Nationally recognised for its importance as a butterfly site.
Every woodland species resident in central southern England is found in the wood, including Pearl-bordered and Small Pearl-bordered Fritillary.
Duke of Burgundy present in small numbers and a few Marsh Fritillary recorded in most years.
Known nationwide as a good site for Purple Emperor.
Bentley Wood is large mixed woodland on the Hants/Wilts border - and yes, OK, so most of it is in Wiltshire! Its importance as a butterfly site is nationally recognised and reinforced through its designation as a Site of Special Scientific Interest (SSSI). More than 35 butterfly species are recorded there regularly, including every woodland species resident in central southern England. Silver-washed Fritillary can be plentiful, and there are populations of White Admiral, Purple Hairstreak, Pearl-bordered Fritillary and Small Pearl-bordered Fritillary. In the case of the latter, Bentley Wood probably has the only remaining colony in Hampshire. White-letter Hairstreak, Duke of Burgundy and Marsh Fritillary also retain a presence. However, it is for the magnificent Purple Emperor that Bentley Wood is perhaps best known.
For visitors approaching from Hampshire, the Tytherley Road entrance is probably most convenient. The car park is reached after about ½ km drive along the track. To see the small fritillaries (Pearl-bordered, Small Pearl-bordered and sometimes Marsh Fritillary), go to the Eastern Clearing (map) by heading on foot 100 yards back down the track, then take the footpath bearing to the left into the clearing (Photo 2). The Pearl-bordered are first on the wing - from around the second week in May, with Small Pearl-bordered appearing typically in the fourth week.
The populations of both Pearl-bordered and Small Pearl-bordered Fritillaries have been declining in recent years, the status of Small Pearls, in particular, giving serious cause for concern. Pearl-bordered Fritillaries are found (now usually only in modest numbers) both in the clearing and also along some of the open rides in the wood. Small Pearl-bordered favour the damper areas in the clearing, including the more recently cleared sections just to the north. Several Small Pearls seen during a visit would be considered a good outcome. Duke of Burgundy is usually recorded during May in very low numbers - look for them in the drier, more tussocky areas of the clearing. In most years, a few Marsh Fritillaries are also reported from the clearing, perhaps as a result of sporadic breeding, or dispersal from nearby sites in Wiltshire.
Photo 2 - The Eastern Clearing - Site For Pearl-bordered Fritillary
If your visit is in July and aimed at the Purple Emperor, they are most active during the mornings, so be there early (eg 9 am). The end of June through until mid-July is usually the best period. Bright or broken cloud conditions with little wind seem to be optimum, but the species is unpredictable. The car park is a good place to wait since the males will occasionally swoop down from a nearby oak and do a circuit or two - sometimes landing briefly on a shiny metallic car or a tyre which has the remnants of dung on it! Visitors occasionally put well-ripened fruit on top of the visitor board to attract Purple Emperors - and with some success. I have also found the switchback as far as the first major cross-tracks to be productive and the gated track behind the car park, with damp areas and animal droppings attracting the butterflies down to feed.
As already indicated, Silver-washed Fritillary can be common (late June and through July) and there can be an unusually high proportion of the normally rare female aberrant form, called valezina, where the golden-brown background colour is replaced by a greenish bronze. A few White Admirals can usually be seen during this period, intricately gliding along the boughs or pausing to feed on brambles.
There are also several small colonies of White-letter Hairstreak around the wood, the best known being close to the Ralph Whitlock memorial. Turn right at the first cross-tracks on the switchback, continue through a slight depression and across another set of cross-tracks until the main track is about to turn right. There are several Elms facing you on this bend (map) which are home to a colony of White-letter Hairstreak. The memorial is a few yards down the minor track to the left where there are more elms (some diseased) and elm suckers, which are also worth a look for White-letter activity.
If your visit is not particularly aimed at a particular species, but simply because Bentley Wood is such an excellent woodland butterfly site, then just enjoy your visit - it is a special place. The different areas of the wood have their own unique characteristics, which reflect in their butterfly populations, and exploration of some of its more remote areas will rarely disappoint.