Life on the surface – July 2018

Hello everyone! We seem to have moved with alarming alacrity into the second half of the year, and the wrong side of the Summer Solstice!

Our woodland spring flowers came and went with jaw-dropping rapidity and our feathered friends have toned the volume down a notch or two on their early-morning vocal calisthenics. Perhaps this is an attempt to conserve some energy for the exhausting business of rearing their young. Many species such as the Tits will have finished with younglings for the year, but others will be on their second or even third brood. I have watched adult Blackbirds gamely dashing to-and-fro feeding juveniles that were the same size as them but still sporting their dowdy, teenage plumage.

Throughout the Animal Kingdom the next generation have been making their presence known. Over the past few weeks, sightings of Fox and Badger cubs, Squirrel kittens and, for the very fortunate, a glimpse of a Hoglet have delighted us.

If, Dear Reader, you enjoyed a stroll through any woodland recently, you may have come across the odd puddle bulging with tadpoles on the verge of sprouting their limbs. Amphibians are not the accomplished parents that many mammals are and these older taddles have faced many perils since hatching from their gelatinous spawn. Those trapped in temporary pools may not survive to adulthood but at least they grew to be too large a mouthful for the Newtings they invariably shared the water with.

The heady scent of citronella pervades the air whenever those of us working in the wood feel the need to repel the swarms of flies and Mini-Biters that are dancing throughout the Reserve, especially those females on the lookout for their next blood meal (see A Taste for BloodSeptember 2011).

Not all the insects that emerge from the pond are unwelcome. The bejewelled Damsels and Dragons are adding flashes of colour to the woodland; the larger species doing their best to keep the numbers of midges and mosquitoes down as they patrol the water course in search of prey. With the Odonata in mind, it is meet that I mention our Dragonfly and Butterfly Walk on Sunday 29th July. We will convene in Quarry Wood at 2pm and do our bit for the Challenge and Big Count 2018.

There will also be a chance to see what moths are around in August when Ralph visits us on the weekend of 25/26th August. The grand opening of the trap will be at the usual time of 10.00 on Sunday morning.

Life, both above and below the water surface, is in full swing, as it is at the surface itself. Not floating on the water but standing and walking on it! How is this feat of Biblical dimensions carried out I hear you ask? Well the first condition is that you must be extremely light, the second being the ability to take advantage of a bit of molecular physics. At this stage any younglings reading this will be leaping around yelling surface tension! For those of you who have not just left school, this is the thin film created at the water/air interface by the attraction of the H2O molecules to each other.

Very few creatures fulfil these criteria for living on the surface film, yet two of the most common are very familiar to us. The Pond Skater (Gerris lacustris) predates our ponds and slow-moving water courses from April through to October. These small insects with the long legs rely on the myriad of tiny creatures that fall into the water and literally get stuck in the ethereal ‘skin’. Sensors in their feet pick up the slightest vibrations in the surface film and they propel themselves with rowing movements of their middle two legs with terrifying speed towards the disturbance. If it turns out to be something tasty the Skater grasps it with its forelegs, pierces it with its sharp rostrum and proceeds to suck the life out of its hapless victim.

One would think that life on the surface would be precarious at best, the danger of breaking through the film and sinking must be ever present. Well Ma Nature is nothing if not ingenious when providing for the denizens of her realm. Each foot of the skater is a pad of miniscule bristles which press into the surface of the water but do not break through. The insect has several thousand tiny hairs on its body which trap air and acts as a hydrophobic surface to repel water. If the Skater is on the receiving end of a stray wave which knocks it into the drink, this layer of air provides the buoyancy to bring it to the surface again.

Pond Skaters share their habitat with another predator which, on the surface (pardon the pun!), does not look suited for life on the thinnest skating arena on the planet. Whirligig Beetles (Gyrinus sp.) would appear to be too bulky as they carry out a bit of community bonding in their hunting groups. However, its streamlined body and flattened middle and hind legs enables the bug to perform its endless gyrations at dizzying speed. As if this is not enough to make it a consummate hunter as well as an elusive prey, the beetle is kitted out with a set of eyes that are divided into two parts allowing it to see both above and below the water surface simultaneously. Very handy if one needs to dive out of harm’s way!

Not all the creatures that utilise the surface film of a body of water skate on top. Aquatic snails such as the Great Pond Snail (Lymnaea stagnalis) and Great Ramshorn Snail (Planorbarius corneus) can be seen crawling along the underneath of the water surface. Both species are pulmonates or lung breathers, taking in oxygen through a cavity on the side of their shells, as opposed to having gills. Thus, the ability to remain at the surface and breathe air from the atmosphere when required is a distinct advantage.

I have often thought that the surface film on a pond is like that part of the globe our species inhabits, though on a much smaller scale. The Earth’s crust supports all human life and unlike the Whirligigs we cannot dive out of danger or fly away like a Pond Skater. This outer skin of the planet is approximately eighteen miles thick on average and it is only the top few feet that provides us with everything we need to exist.

“Look again at that dot. That’s here, that’s home, that’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every “superstar,” every “supreme leader,” every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam.”

Carl Sagan (1934-96)

Food for thought, life at the surface is precarious indeed!

Put me right at pgcrow@yahoo.com

Paul Johnson

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Image credits:
Img 1: Blackbird feeding time by Tom Sowerby, used under Creative Commons License 2.0; img 2: Fox cub looking out by Peter Trimming, used under CC2.0; img 3: Hedgehog – Erinaceus europaeus by Mick Talbot, used under CC2.0; img 4: Tadpoles by Stephanie Wallace, used under CC2.0; img 5: Frogpole by Danny Chapman, used under CC2.0; img 8: Pondskater by S. Rae, used under CC2.0; img 9: Whirligig Beetles Up-Close by Stan Lupo, used under CC2.0.

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