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WHIRLIGIG BEETLES SWARM IN THE SUNSHINE by Adrian Chalkley
HUNTING FOR THE OAK POLYPORE FUNGUS by Neil Mahler

WHIRLIGIG BEETLES SWARM IN THE SUNSHINE

There are 12 species of whirligig beetles that can be found in UK waters and it is well known that they are quite a sociable insect, often occurring in some numbers whirling rapidly about apparently at random on stretches of open water. It is mentioned in several books that ‘schools’ of hundreds of individuals may occur in late summer. I have often seen them in groups of say 10 to 25, but whilst I was recording for the Essex and Suffolk Water Company at their Lound Reservoir in September I saw more whirligigs than I had ever seen before.

On one of the lakes, about five metres out from the shore I could see from some distance as I approached what appeared to be a long, sinuous patch of sparkling water; as if the sun was reflecting off a large oil slick. As I got closer I could see this ‘slick’ was made up of hundreds of whirligigs slowly whirling around as the sun reflected off their backs.

For the most part they were content to swim slowly around each other, but every so often a small patch would become more agitated and whirl around at great speed and then for no apparent reason go back to their slow procession. They reminded me of the Milky Way viewed on a really dark winter’s night, with the stars twinkling in the blackness.

Only when I estimated the size of the gathering did the numbers really astound me. I estimated the area covered by the school of beetles was about 1.5 metres across and, as it made a sinuous shape parallel to the bank, I paced out the length which was 15 metres! Now on a conservative estimate there were at least 100 whirligigs in each square metre, possibly 150. This gives a total of 1.5 x 100 x 15 = 2,250 or 3,375 beetles if you take the upper estimate of 150 per square metre.

There were also large numbers of stray beetles wandering to and fro away from the main swarm, both towards me and towards the opposite bank. So I am sure that there must have been 2,500 to 3,500 individuals on that part of the lake. Elsewhere on the four lakes I monitored at the site I saw small numbers of 10 or so at most backside locations I went to, so how large a population has been established there I will leave you to judge. I recorded two species at Lound by the way, Gyrinus substriatus and G. marinus. I should love to know what caused such a large swarm in one place and if it was one species or two.

It may be worth noting that the sun reflecting off the whirligigs back is due to the cuticle covering its upper surface. The dorsal surfaces of the head, thorax and elytra are water repellent and like many waxy surfaces reflect light well causing the silvery colour. The ventral or lower surface is the opposite in that it attracts the water or is hydrophilic. Thus a whirligig will float always at the same level because its cuticle forces it to do so with no effort at all. This level allows a ‘moustache’ of sensitive hairs to detect small waves reflected from prey. The seemingly random swimming generates suitable waves to be reflected from prey in much the same way as a bat’s echo location.

Gyrinus marinus has been recorded infrequently in Suffolk before, and this is a good record in view of the very few times it has been found. It has been recorded often in Norfolk and its presence at Lound may therefore be expected. Despite its name it does not seem to be associated with coastal sites. What makes it interesting here is the large population that was recorded which may be a result of the second brood of the year having hatched recently, as happens generally in the autumn. The autumn brood is the one to hibernate.

I would ask any readers with observations to make on the above to get in touch with White Admiral or put a comment on the Suffolk Nature Blog at http:// snblog.boxvalley.co.uk/

Adrian Chalkley Freshwater Invertebrate Recorder

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HUNTING FOR THE OAK POLYPORE FUNGUS

This year I was determined to find the Oak Polypore Piptoporus quercinus so, knowing it had been recorded there, I headed off to Captain’s Wood, the new Suffolk Wildlife Trust (SWT) reserve at Sudbourne. Before looking it is important to know when it appears (July to September), what it grows on (oak heartwood at least 250 years old) and what it looks like (a golden birch polypore bracket fungus). Captain’s Wood could be called a ‘mini-Staverton Park’, but whereas Staverton has well over 4,000 ancient oaks, Captain’s Wood has at a very rough estimate only 200 or so but many other species of tree besides. The predominant undergrowth in both cases is bracken except in parts of Staverton where it is crowded out by denser trees and of course its famous holly trees.

I started my search towards the end of July. I had already acquainted myself with the wood in the spring before the bracken emerged when looking for small discomycete fungi. However, I was not prepared for the amount of dead sweet-chestnut logs and stumps, which are similar in appearance to oak and I wasted a lot of time checking these before I realised they were not oak. Two fungi that can be mistaken for Oak Polypore are Chicken of the Woods Laetiporus sulphureus and Beefsteak or Liver fungus Fistulina hepatica and both of these were present.

Eventually I found a clearing at the far end of the wood where the SWT had taken out a lot of Rhododendron ponticum, thereby exposing some marvellous ancient oaks. Because of the rhododendron the bracken had not been able to get a strong foothold; perhaps the only thing rhododendron is good for! It wasn’t long before I shouted “bingo” – my first oak polypore!

Having only recently emerged it was rather small, only four inches wide. Just above it about eight inches away was an even smaller fruiting body, which subsequently failed to develop. It is illegal to remove or even take a sample of this fungus without permission but I was confident of my identification. I took several photos and tried to work out a grid reference, and then continued my search. I failed to find further specimens that day, but the season had only just begun.

Back home I reported my find to the SWT in case it was at a location different from the existing record. Steve Aylward got back to me wanting more detail. He told me that oak polypore had not actually been found in the reserve but in a privately owned part of Captain’s Wood where five fruiting bodies were discovered in August 2001 and he asked to be taken to see it. When we met the following morning I was dismayed to see that part of the fungus was missing. We presumed it had been bitten by a fallow deer but it is possible that a hare that I had previously seen in the clearing had been able to reach it. I surrounded the trunk with tree brashings and hoped it would continue to grow. A week later I found that the bracket was growing. I returned every few days to photograph its development until the end of August when it was so heavy that it fell off.

I was gratified to have my identification confirmed by Martyn Ainsworth, the fungal consultant for English Nature (now Natural England). He had asked me to send him a small dried sample that has now been deposited at Kew.

I was now sufficiently motivated to search in Staverton too. On the first day I found six fruiting bodies, and eventually more than 20, including one 12 feet up a tree. This number was higher than Chicken of the Woods or Beefsteak fungus seen during the same period, which gives a false impression of the abundance of Oak Polypore. It is classified as endangered in Britain and is protected under Schedule 8 of the Wildlife and Countryside Act 1981 and is a BAP species. I have read that one is unlikely to find oak polypore under shaded trees such as holly but in Staverton Thicks I found it growing on oak logs in two such locations.

In my humble opinion SWT’s management of Captain’s Wood will protect the oak polypore and while I am sure it is safe in Staverton I wonder if planting new oaks in blocks only at the western edge of the park is as good for the fungus as filling in the large gaps elsewhere?

Neil Mahler

Oak polypore in Captain’s Wood with damage visible on the left hand side

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