20-July London’s July Wildlings: Adders, Algae & Aquatic Spectacles

Adders are still pregnant this month, but grass snakes are laying eggs. When the female grass snake has her eggs laid, she coils herself around them and hisses at any visitors. She will even attempt to strike, although she has no poisonous fangs. Young grass snakes are a mere one and a half centimetres long when they hatch and, being so vulnerable, are rarely seen.

July is one of the best times to see adders. The females seem to have a compulsion to bask in the sun more this month. Normally, in other months you tend to see a female with some attendant males, but this month you tend to encounter far fewer males, although their sloughed skins are seen occasionally.

Basking adders are met with great fear by most Londoners. It does happen to be the only wild creature in the capital which is capable of killing a resident, although the truth is less dramatic. They seem incapable of killing a fully grown, healthy person, although they have been known to kill a child. Snake bites are rare and over sixty per cent of them are dry i.e. contain no venom. The best advice for avoiding a bite is probably to tread more heavily on the ground where you think they may be found. This is usually enough to send them on their way. Otherwise, just carefully walk around one that has been seen, giving it a wide berth.

Unsurprisingly, there is a rich folklore associated with such a dangerous animal. They were thought to be deaf, prone to swallowing their young, capable of killing a bird by spitting at it and fond of dancing. The latter has a ring of truth for anyone who has seen them courting. They were also thought to particularly dislike being struck by an ash twig. Consequently, these twigs were carried on country walks in case they were encountered. Alternatively, if you could persuade a spider to run across an adder’s back, the adder would immediately kill itself. If bitten, the ‘cures’ were legion. Adder liver oil was a favourite among Surrey shepherds. Elsewhere, deep fried adder fat, warm pigeon flesh, Venice treacle or a bag containing the heads of an adder, toad and newt were all thought to be equally invaluable. Other concoctions for the same purpose contained such exotics as baysalt, stamped rue, pickled herring and deer suet. However, it is still worth taking care around the southern perimeter of London, especially on any sandy or chalky heaths which is where these snakes choose to live.

Amphibians

When young, these two newts can be difficult to separate. Smooth newts tend to have a yellow or orange belly, whereas in palmate newts it is pink or brown. Great crested newts are still laying eggs, perhaps two or three each day, often just after a shower of rain. Towards the end of the month the adults will leave their breeding ponds to spend more time on land.

Fish

Insect Emergences

The quieter stretches of rivers such as the river Darent and river Crane are good places to look for these emergences. Mayflies you may see include the small dark olive Baetis scambus, a minnow mayfly Centroptilum luteolum and the most common mayfly you are likely to see when pond dipping, the pond olive Cloeon dipterum. This last species can vary a lot in colour from olive to brown and then darken even more with age. A small mayfly, the Angler’s curse Caenis macrura is even known to alight on an angler’s clothing and turn from a dun into an olive in just a few seconds. Caddis flies, or sedges as anglers call them, swarm at this time of year. So many can emerge they can cover nearby bright windows in what looks like a seething mass of moths. These swarms are generally over water or around trees nearby and can include larger impressive caddis flies such as Potamophylax latipennis.

Other water bodies in July can turn bright green due to algal blooms or get covered in filamentous algae (blanketweed), duckweed or other aggressive alien flowering plants. Typical blooms in London’s reservoirs include countless diatoms such as Asterionella and Scenedesmus. Filamentous algae such as Oedogonium, Spirogyra and Oscillatoria are responsible for the blanketweed that can quickly choke ponds. The latter species is so called because it is a filamentous alga that can and does oscillate.

Duckweeds Lemna spp. are a universal nuisance covering London’s ponds. There are in fact six different ones. Great duckweed L. polyrhiza (10 mm.) is the largest, then Common duckweed (4 mm.) which is the most common. Least duckweed L. minuta has leaves only 1-2·5 mm long and Rootless duckweed Wolffia arrhiza (0·5-2 mm.) is even smaller. Ivy-leaved duckweed L. trisulca is quite different. Its leaves are darker, translucent and it has more pointed leaves than the others and it is usually found just below the surface of the water. Even more curious than the duckweeds which are our tiniest flowering plants are the floating fern Azolla filiculoides and floating liverwort Ricciocarpus natans which are both occasionally found on London ponds. The latter species can be found in Epping forest and Walthamstow marshes boasts four different duckweeds including the Fat duckweed L. gibba (3-5 mm.).

One last aggressive alien flowering plant that is starting to choke parts of the river Colne is Floating pennywort Hydrocotyle ranunculoides. As it can grow from just a discarded fragment and then continue to grow up to 22 cms. in length per day it could present quite a problem for the future.