Thanks to volunteer Phil for his wonderful report and photos featuring just some of our lovely butterflies.
This is the final article in a series about butterflies to be seen on the reserve. Part 1 gives some summary information about where to see butterflies on the reserve and the types of flowers used.
When starting this series I hadn’t intended to feature our resident hairstreaks but they are starting to emerge for the summer. It is worth noting that a number of well know butterfly identification guides are rather out of date when it comes to flight periods and with climate change many species are appearing perhaps 2-3 weeks earlier than previously indicated.
The brown hairstreak is an elusive butterfly and it spends much of its time feeding on aphid honeydew in the tops of trees. The females however will descend to lay eggs on new growth in the blackthorn bushes and this gives the best chance to see them. These photos of somewhat worn specimens were taken at Pulborough in September 2017.
The purple hairstreak is not so much uncommon as difficult to observe because of it’s liking for oak trees on which its caterpillars depend for food. I finally had my first ever sighting of a purple hairstreak at Knepp last year. It proved awkward to photograph half hidden in the lower foliage of a large oak.
When flying the most noticeable colour was the light grey of the underwings. The purple colours can only be seen on the upperwings, more extensively in the males than the females, and may not be easy to observe above head height.
Every year at this time we have a few silver washed fritillaries in our woodlands which also depend on oak trees for their lifecycle. These large and beautiful butterflies may be seen in any of our woodland areas and last year there have been reports from Black Wood and the wooded area on the lower part of the path to Nettley’s hide. The males are a vivid orange colour with brown markings as in this photo from Southwater Woods near Horsham.
The females are similar but less vivid with a slightly different pattern of brown markings. This female seen near Nettley’s Hide had been laying eggs in the bark of an oak tree before coming down to the ground.
When hatched the caterpillars will hibernate in the tree and then descend in spring to feed on violets. The butterfly’s name refers to the silver streaks seen on the underside as in this photo taken at Bookham Common near Leatherhead – an excellent site for this species.
A much more common species which is considerably smaller but has a colour resemblance to the silver washed and other fritillaries is the comma. There are many commas on the site just now which are easily identified by their orange and brown markings and their curious ragged wing edges.
These butterflies tend to be seen more around the bushes and trees but could be seen almost anywhere on the reserve. This tends to be true also of the speckled wood.
This common but attractive butterfly is happy in shade, so can be seen even on dull days when other butterflies stay under cover. It typically has 3 broods per year and can be seen on the wing from early spring until well into the autumn. The upperwing and underwing patterns are very similar.
A few common species can be seen for much of the year including red admiral, peacock and small tortoiseshell. While looking very different they all have one thing in common in that they all lay eggs on nettles, a plant also used by the comma.
The well-known and striking red admiral is principally an immigrant from the continent which arrive in force in May and June. These butterflies will then mate and UK bred butterflies will emerge during the period August to October. Some adults, but only a small percentage of the population are now thought to overwinter in the relatively warm south of the UK and it seems likely that any sightings much earlier in the year will be from this population. Most visitors will recognise the red admiral upperwing pattern, but the much more cryptic underwing is not so well known.
The equally well known and beautiful peacock butterflies hibernate and re-emerge in spring to breed again with the new brood starting to emerge as adults in July. The underwings however are a very plain brown. These photos were taken near my home.
The caterpillars often congregate in large numbers on nettles and can sometimes be seen prominently at this time of year.
The beautifully patterned small tortoiseshell has less plain underwings than the peacock but has a very similar lifecycle, although the caterpillars don’t congregate in the same way.
Without exception all the butterflies in these articles have been seen on the reserve in July either by myself or by other people I know but with so many species to cover I decided to double check to see if any obvious candidates were missing. I duly found two species typically found on our flowery path margins that I’d not seen for some time.
Painted ladies may be seen in July and particularly like to feed and lay eggs on thistle plants. Sometimes they appear in the UK in very large numbers and 2019 was one of those years so there were more than usual on the reserve.
Painted ladies have an extraordinary journey to the UK from North Africa through the spring and summer and take a number of broods during their migration through Europe to reach here. More about this fascinating butterfly can be found in a blog entry written in 2019 at this link:
https://community.rspb.org.uk/placestovisit/pulboroughbrooks/b/pulboroughbrooks-blog/posts/recent-sightings-late-june-and-july---the-amazing-painted-lady.
The small heath is a fairly common species of grasslands and yet has not been recorded on the reserve until 2019 when a small number were seen by the paths from Redstart Corner into Adder Alley. As they are small and usually fly low to the ground, it is entirely possible that they have simply been overlooked. They appear to have a liking for short grass so the Adder Alley path and the grass near the pond at Redstart Corner provide perfect spots for them.
Small heaths will visit various of grassland flowers and lay eggs on a variety of grasses. There are 2 t broods per year from late April through May and June, and then again from late July through to September. This specimen seen on 10th July on the bracken next to Adder Alley looks rather faded so is more likely to be from the first brood.
Small heaths are a brown and orange butterfly with the underwings looking rather like a much smaller version of the ubiquitous meadow brown. Their upper wings are however completely orange but rarely noticed because they always perch with wings folded. This photo of 2 males sparring taken near my home give some idea of the orange colour but only because it is backlit. The circular spots on the wings are only seen on the undersides and are easily seen when in normal pose.
When passing down the Zigzag Path there is a high hedgerow with much blackthorn and some taller trees on the right hand side. A few of the trees are the suckers growing from the roots of old English Elms killed by Dutch Elm disease. Suckers will never grow so tall as the proper trees reaching certain height and then dying off but nevertheless these elms can still support a butterfly that is completely reliant on this type of tree for its lifecycle. This is the white letter hairstreak, so called because a thin white line on the underneath of its hindwing resembles a letter W. In this photo the hairstreak line can be seen but the W shape is so faint it is almost invisible and cannot be seen without zooming in.
They always perch with wings closed so the very dark brown, almost black colour of the upper wings is very rarely seen.
A small colony of these butterflies was first discovered in the elm suckers in 2018 and observed again last year when the photo was taken.
White letter hairstreak caterpillars feed exclusively on elm leaves but as well as English elm, wych elm is also used. Fortunately, while Dutch Elm Disease was a disaster for this butterfly the growth of suckers has provided a lifeline for it survive and even slowly expand its range in the UK.
These are small butterflies and not so easy to spot so you may need to spend some time looking up into the elms with binoculars and hoping to detect some movement. Like the other hairstreak species, the white letter hairstreak feeds mostly on aphid honeydew in the trees, but it is worth checking any thistle or bramble flowers nearby as they will sometimes descend to feed there. July is the peak month to find them and they have a flight period of only a few weeks.
The White Admiral – a beautiful dark brown and white butterfly that in recent years has been annually spotted in small numbers in our woodland on the South side of the reserve. It seems therefore that we do have an established colony. I have never managed to find one there, but I did manage to see one in Southwater Woods near Horsham very recently.
These are medium to large woodland butterflies feeding on honeydew in the canopy but sometimes descending to feed on bramble flowers and animal droppings from they can extract moisture and useful minerals.
I was astonished to discover just a few days ago that there is a population in my local woods on the North Downs, and this specimen is feeding on a bramble flower nearby.
Note the damage to the wing edges which is apparently a common issue with white admirals as they investigate the inner reaches of brambles. Females lay eggs exclusively on honeysuckle on which the caterpillars feed and as they are normally intertwined with other plants more damage may occur during the process.
Perhaps the most remarkable think about white admirals is their flight pattern. While most butterflies have a fluttering sort of flight, white admirals spend much more time gliding giving a very graceful appearance.
Despite its name the species is not related to the much more common red admiral. The pattern of its wing markings both above and below make it clear that this is actually a close relative of another woodland species, the much larger purple emperor.
Purple emperors are famous as elusive but very large butterflies, and for the males’ bright purple and white upper wing markings. It is less well known is that the purple is an iridescent sheen and the light must be just right otherwise it will simply appear to be dark brown as in the even larger female.
There have been very occasional records of purple emperor at Pulborough Brooks before. However in one week in late June / early July this year there were 2 sightings. First a male was seen on the ground near the Visitor Centre showing off his purple sheen. Unfortunately there was no camera to hand.
The on Friday 3rd July I was standing at the Hanger when a large fluttering presence entered my peripheral vision. I instinctively looked up at the sawn of branch stump in the oak tree above the lower viewpoint to see if the butterfly had gone there. I had noticed before the sap exposed here had been attracting red admirals and hornets. Sure enough a large butterfly was perched up there and I immediately recognised it as a purple emperor. Happily I was able to take a few photos of both upper and under wings.
Note that the wing pattern is very similar to the white admiral. There is no purple showing but the pattern of white markings on the upper forewings marks this out as a female as there is a slight difference in pattern from the male. These are bigger than the males and are the UK’s 2nd largest butterfly, behind the female swallowtail which in the UK is largely confined to the Norfolk Broads.
Although purple emperors spend much of their time high in the woodland canopy they do sometimes come to ground, particularly in the morning. Here they use animal droppings in the same way as white admirals.
This raises the question are these butterflies passing through or could we actually have a colony on the reserve? Purple emperors feed on honeydew in trees and exposed sap with oaks being a favoured species but they also need tall trees which they select as a “master tree” where the males gather as a lookout post for passing females. Taller trees on high points provide good sight lines. There is no shortage of suitable trees on the reserve.
Most important however is the foodplant for the caterpillars and this is provided almost exclusively by sallows – a type of small willow sometimes known as goat willow or pussy willow. Occasionally grey willow or crack willow is used. I am not sure about the presence of sallows on the reserve, but they are quite common in UK woodland so it seems likely that we have some on the site.
It seems unlikely that purple emperors are established on the reserve otherwise there would probably have been more sightings in recent years. However the fact that 2 have turned up recently and the fact that we do have almost certainly have suitable habitat suggests there is a reasonable possibility they could become established. It would be helpful for any visitors to report definite or suspected sightings of this impressive but elusive species.
In total this series of articles has covered 23 species of butterfly, which is about 40% of total number of UK species. A few others can be seen here at other times of year, the orange tip in early spring being a good example. Many of the other species however have much more specialised habitats and consequently restricted ranges which preclude then being seen at Pulborough. However we are fortunate to have a wide range of species that provides a continuing source of interest in the reserve through the summer months.