19th July 2018
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Learning about stick insects, masters of their niche in damp places

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Sticks are sticks and legs are legs, but you don’t expect to find one growing out of the other. That is exactly what my visitors found. While paddling about in a natural mini freshwater pool, the lasses, Rosie Allan, Shara Soobie and Vaila Irvine, had come upon a totally alien weirdo. The lads, Lenny Allan and Bradley Sharp, hearing their excitement, had run to see what they had found. The initial shock of the unfamiliar gave way to excited fascination and burning curiosity took the five wildlife-watching bairns to our door, bearing the stick with legs.

I recognised the oddity as a clearly remembered character from my own childhood. A short, brownish, speckled stick lay at the bottom of a plastic container which they had carried round. It lay inert and soggy at the bottom of a plastic cone they had found to put it in. Closer inspection revealed a mass of tiny brown flakes, rather than the single organic entity of a stick. This was a stick covered in bits of something; fragments of leaves maybe, or minute particles of wood or cardboard. A flash of startling white and a brilliant blue speck must surely have been a chip of chewed up print.

We soon had it comfortably, but very temporarily, housed in a glass pudding dish, in case the legs appeared and the creature tried to run away. We stood the glass dish onto a sheet of white paper so that it was easier to see, against a plain background. A brief wrestling match with flex, chair legs and table legs secured a small electric desk lamp and completed the initial preparations. Five eager faces squinted through a hand lens and there, revealed in all its magnificent detail. At the bottom of the bowl it lay like a minute, freckly log. The bairns were dismayed that the “legs” had disappeared, and described what they had looked like.

We waited. Still no legs in evidence yet. The log, slightly wider at one end than the other, appeared to be hollow. I described a possible Caddis Fly larva, but my visitors were none the wiser. It was time for books. Half a dozen different freshwater life volumes of assorted sizes and different target audiences were laid out and five sets of helpful fingers began to slide along index columns.

We soon had a small gallery of illustrations and diagrams laid out before us. Some books had little or no information about Trichoptera, others had more. The Burke Young Specialist series is always good for clear, simple illustrations and everyone could see at once how the log was in fact a long, round case; a “home” for the soft larva inside.

Suddenly the cry went up. Legs had emerged, and also a head. A tiny, rounded head poked out from the wider end of the stick, and a few fine, pointed little feet were visible to either side. The bairns were concerned, since viewing the illustrations, that water might be urgently needed. Thankfully I hoard junk, so clean, empty yoghurt pots were on hand and the team trooped out to find pockets of fresh, clear rainwater, here and there about the house. In no time they were back, carefully carrying small quantities of fresh water.

Pouring the water into the bowl meant that the flow dislodged the “log” best, which scrabbled frantically for a foothold. Finally all was settled and then we watched as the stick with legs began to explore the bowl floor, hauling its case around behind it.

We had a great time reading through all the accounts of the creature, struggling to pronounce all the Latin names and puzzling over the fact that no two reference books listed the same species. At least all the books agreed that Caddis flies belonged to the order Trich­optera, or “hairy wings”. As ever, it was Edmund San­dars who won. His An Insect Book for the Pocket (1946) is my favourite book on the subject. Nothing else I have ever seen compares with it for detailed information and description of its life cycle, biology and habits.

Sandars’ text may be 70 years old and its Latin names may be well out of date, but the way he writes about the hundreds of insects in the book brings them to life before you. These “sticks with legs” are masters of their niche in wet places. There are apparently around 200 different species. The flight stage creatures, the “moth winged” Caddis flies live a few days or weeks at the most. They don’t even all have proper mouths and can more or less only lick up moisture and possibly nectar. They are required for breeding purposes only and can be seen swarming in the evening air above ponds and streams in summer.

Eggs, held in jelly masses of 100 or so at a time, are dropped by fertilised females, straight into the water, says Mr Sandars. The jelly dissolves and individual eggs lodge against crevices in the stream bed hatch in anything from 10 to 24 days. Edmund Sandars actually kept and recorded details on most of the creatures he describes. The tiny caddis pupae receive oxygen through their skin until they develop gills. The cases are built from whatever loose material is lying to hand. Silk is spun from glands in the head and used to glue the fragments into the case shape.

The larva can live inside the case, feeding with the help of powerful claws and jaws, for up to 10 months. Some species make cases out of tiny shells they find in the water, others make them out of sand grains. A few species make burrows instead and another builds small stone shelters. Some attach their cases atop reeds and stones to stop them being washed away, others crawl freely over the pond or stream beds on their prowl for food. There are carnivorous species, vegetarian and even omnivorous caddis species.

Finally the time for the last phase of their cycle. The larva spins a silken sieve at each end of the case, fastening it securely to solid objects. They withdraw and exist in an inert, hidden period as a pupa while immense changes occur in their bodies. Just before they are ready for the adults to emerge, the pupa suddenly becomes very active. Powerful jaws allow it to chew its way out of its shell and feathered legs help it swim straight up to the surface, where almost instantly the adult fly emerges and is soon freely flying.

We studied the peerie speckle shelled fellow in the bowl with considerably more respect than before. What a palaver of a life it would have. I recalled with some guilt, the experiment we had carried out at primary school in Essex in the 1950s. We placed a Caddis larva into a bowl of fresh water into which a tub of tiny, gaudy glass beads had been tipped. After a few minutes, the creature crawled out of its shell stick home and set about building a new one, entirely out of glass beads. We were delighted of course and carefully placed the poor mite back into the pond, where it stood out like a glorious sore thumb. These days, attitudes have changed. We know more about lives and needs of crea­tures and experiments and over collecting are rare.

It was time for the bairns to go. We had had a great time and I promised them that as soon as I had photo­graphed and drawn it, I would let the little “Stick with legs” go again. It’s incredible to reflect on all the hundreds and thousands of life cycles slowly winding their precarious, tentative, wily and opportunist way through the seasons in every single part of every habitat around us. I for one will keep an eye out for the moth winged swarms this summer and I will keep an eye out for the bairns too, who had another surprise for me, before the day was done; but that’s another story.

Jill Slee Blackadder