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This A-Z of nature on the canal is reprinted from a series which originally appeared in the Trust magazine, Dragonfly. Alder [Alnus glutinosa].A very common canal side tree easily recognised by its black fissured bark and dull green broad, unpointed leaves, and in winter by its long attractive catkins, which hang like lambs tails, and dry seed heads which resemble small fir cones. Although it will eventually form a medium size tree it usually occurs more as a clump at the waters edge. It is able to thrive here, where other trees would find it too wet, because its roots are able to form an association with bacteria which can utilise atmospheric nitrogen. There is little nitrogen in waterlogged soil so without this ability the Alder, like most plants, would find it difficult to grow. Indeed, the Alder actually ‘makes’ more nitrogen than it can use, so over time it builds up the fertility of the surrounding soil. Alderfly [Sialis fulginosa and Sialis lutaria].These dull brown insects are related to the snakeflies and lacewings and fly in early summer. They settle, with their wings held roof like over their bodies, in large numbers on canal side plants, including the Alder hence the name. There are two species, both are poor fliers and only live about three weeks. There only role as adults is to mate and lay eggs. They usually never even feed! They lay about 500 eggs on plants and stones near the water. after 10 to 14 days the brown larvae hatch and enter the water where they live under stones or in the mud. They prey on other small water creatures and they themselves are eaten by fish. Those that survive take up to two years to grow to full size [2.5cm/1"long], then they leave the water to spend their three week pupal stage in mud and debris on land whilst they change into a flying insect ready to begin the cycle again. |
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