Snails hoist yellow flags
yellow flags include Jacob’s Sword and Segg – the AngloSaxon word for a short sword.
Up to three deep yellow blooms per stem are produced successively in the summer months, each with three upright petals (“standards”) and three “falls” – coloured sepals that turn down towards the stem.
The flowers are pollinated by bumble bees who follow the dark brown lines radiating along the large petal-like sepals from the nectar source. After pollination, green seed capsules, looking like miniature cucumbers, are formed which split when ripe to release smooth, flat seeds – ideally shaped to float away with the current to a new site.
Irises also spread locally by growth of the rhizomes (thick, underground stems) from which this perennial plant re-grows each year. The boiled roots were sometimes used for soothing bruises and cramps and were powdered to make snuff.
Many freshwater snails are found among the tangled vegetation that grows along the banks of our canals and they can be spotted at the surface in summer. The great pond snail (shown above) has a shell with a sharply pointed spire that can grow to 6 cm high; the ramshorn snail is smaller and has a flat, coiled shell. These two common snails are both pulmonates that need to come to the surface to breathe in air through a closable breathing pore.
Another group of water snails, the operculates, breathe through gills, like fish, taking their oxygen directly from the water. They can be recognised by a plate, known as an operculum, attached to their foot which they use to close their shells. They need running fresh water, rich in oxygen, so are not found so commonly in canals.
The shell of a snail has two layers: the horny outer layer provides a waterproof covering for the tough chalky layer beneath. Snails do not need to shed their shells in order to grow but lay down new material at the mouth of the shell. Little wrinkles or slightly different patches of colour – a bit like tree rings – may show the boundaries between periods of different rates of growth.
The diet of water snails largely comprises the thin layer of micro-organisms, such as algae, that grow over the underwater surface of vegetation. The tongue (radula) of a snail is covered with rows of microscopic teeth that efficiently scour the algal film. Decayed remains of pond weed are also eaten and the great pond snail will eat small, dead fish and softbodied invertebrates. The mouth of a snail is actually on its foot (the flat sole on which they glide along): hence gastro (mouth) pod (foot) – snails are molluscs from the class Gastropoda.
Snails are prolific breeders, which is as well since they are eaten by waterfowl, fish, newts, great diving beetles and even other pond snails. Each great pond snail (they are hermaphrodite) lays up to about 100 eggs, attaching the large gelatinous mass to weeds and other objects.
Enjoy the beauties and curiosities of summer.