Collecting caddis
Health & Safety
Caddis are found in freshwaters that carry the usual dangers of drowning and exposure if wet and diseases that can be avoided by and large by covering cuts with a waterproof dressing and washing hands before eating.
These notes are intended to enable collectors to get the biggest range of species from a site – not for quantitative repeatable samples, but imagination can enable many to be adapted for that purpose.
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The pond net
Used in a variety of ways, this is the best all-round tool.
From moderate to fast flowing shallow water
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The main method here is called kick sampling and involves disturbing the smaller stones and gravel, or sand or weed bed just upstream of the net that is held firmly against the bottom. Feet, hence the name of the method as kick sampling, or a rake, are be used to disturb the bottom.
The procedure relies on the current sweeping dislodged material into the net. The contents of the net are spread into a shallow tray of water and carefully scrutinized for caddis. This kick sampling method is used, in a standardized way for water quality analysis throughout the water and regulatory industries. However, as far as caddis are concerned, a number of things can go wrong that prevent you getting a good catch of species.
The method relies on water flow to transport the dislodged material. Many caddis live in cases that are specifically designed to avoid being swept away by current as they use large sand-grains in their construction. These often drop put before reaching the net. This is clearly a major problem in slower flows but a way round it is to swirl the net vigorously above the disturbed area soon after kicking.
Another problem is that kicking may not dislodge firmly attached caddis. The standard water analysis adds a minute of scrubbing (by hand or with a brush) the top and bottom of rocks. Hold the rock in the mouth of the net so the dislodged material washes into it.
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Kick sampling can be modified for small streams even tiny runnels by using smaller and smaller nets such as aquarists fish handling nets or even tea-strainers and disturbing the bottom by hand. These are handy nets to consider having in a ruc-sac; a kitchen sieve is also useful as a robust net on occasions. At the other end of the spectrum other species that might be missed reside under large stones that are just too big to be kicked over. Two people are very useful here as one can struggle ashore (sorry with full regard for lifting safely) and put the rock into a tray while the other does a quick kick and/or swirl and/or sediment-grabbed- by- hand from the hole left behind into a net. The big rock can be scrutinized for attached caddis larvae and pupal cases, and other caddis will crawl off into the tray.
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Submerged wood is another vey good habitat and has its own specialists. It is a matter of bringing bits of wood ashore into trays and scrutinizing them for attached caddis and looking into the tray for what has crawled off, and do not forget what is left in the hole after the wood has been moved.
Remember the honorary rocks and timber i.e. the famous old bicycle or pile of bricks. In some muddy sites these provide a valuable firm substratum and are a magnet for caddis who find.
Tree roots are another excellent habitat to scrutinize for caddis, and many other taxa too. They combine many physical features of firmness that caddis like for attachment but also a filamentous nature to allow caddis to hide and shelter from the current.
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Still waters
The net is again the main tool and used to move through the weed or along the bottom, or by swirling, over disturbed bottom of overturned stones.
The key to success is to avoid collecting too much debris. There is little merit in working over fine soft bottoms or digging the net into the bottom as you will have a lot of sorting for little reward.
Once again, the larger stones and wood brought ashore will prove very profitable. The size of the water body can be reflected by size of net used, and remember that even small puddles have their species.
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Viewing tube
In clear water, this is a very effective way of seeing the bottom and detecting caddis that can then be collected by forceps, or sucking pipette, and a turkey baster with the end sawn off to make a SLIGHTLY bigger hole is useful, but if the hole is too big the caddis drop out far too. Stones and logs can be over-turned and the caddis seen underneath but be aware of the fine debris swirl that can obscure visibility. This works best where a gentle current can carry away the silt, but some holes under rocks seem to be able to generate a never-ending stream of muck.
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Hand-sorting through debris
Picking up small amounts of wed or plant debris and searching through it is often successful – in fact often more so than using a net as the latter often gets quickly clogged with filamentous algae, for example.
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There is a large larva of glyphotaelius pellucidus in the middle of this handful of leaves.
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The latter can even be recorded without getting hands wet as it cuts circles out of leaves to make its case which can be looked for on the bottom of leaf-filled pools.
Sorting tray method
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One of the techniques to learn is the use of the sorting tray. This can be as small as a margarine tub or as big as you can carry. Whatever size is involved the key is not to put too much into the tray or you will never see the caddis from the debris in a reasonable time. Too little, and you have a lot of tray’s worth to get through a nets collection. With experience you go for a balance between the amount of debris collected in a net and the amount that can be spread out into a tray or you could find caddis have crawled out of the net before all the sample has been dealt with. The picture shows about a third debris to 2 thirds bare bottom.
Caddis can take a little time to become active after being dumped into the tray of water so the bowl shown wants to be left and scrutinized for about ten minutes, with only gentle disturbing it with forceps or sucker or tea-spoon as lifter. As it can take them a while to become active, continual stirring the contents is counter-productive.
Trickling rock faces
If there is permanent flow then look for the galleries of Tinodes stuck to the rock and do not forget the puddles at the bottom of the trickle or the roots of plants growing in it - all are potential caddis habitat.
Temporary water-bodies
Many marshes, ditches, ponds and pools dry up completely during summer. This is the particular habitat of caddis of the family Limnephilidae, and a few others. The adults pass the dry summer and mate and lay in the damp bottom in early Autumn. The eggs are in jelly that swells up and protects them until the water body floods and they can finally escape and start feeding on the plant litter.
These people are searching for caddis. This dry oak woodland may not look caddis habitat, but is for our only terrestrial species, the enigmatic Enoicyla pusilla that lives on the Herefordshire, Worcestershire, Shropshire borders.
Habitat damage in small water bodies
In a large water body it is difficult to wreck a site, but that is not the case for smaller sites, and the smaller the site the easier it is. A particular stone, often quite small, or piece of wood, can be the major hard substratum in a tiny stream and their disturbance can be highly significant to those living on and under them.
Remember also that in a small stream the large moss-covered boulder that rightly attracts you as a recorder has that moss cover because it is not disturbed and rolled around by winter floods. Once disturbed it will probably not bed back and be rolled the next flood and the whole habitat lost.
Nothing unusual in the warning, it is standard practice not to remove all of any habitat during natural history recording.
The worst habitat to survey
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The middle of a reed-swamp takes some beating as the debris is full of caddis-cased sized pieces of debris, and the habitat is difficult to penetrate.
Fortunately they have edges and rides!
It is seriously worth considering going for adults in such difficult habitats.
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Collecting adults
As with many insects they can be caught in nets designed to catch flying insects. Many species rest on vegetation during the day and can be dislodged by sweeping the net through the plants, but the caddis soon take to the wing so sweeping into a net that has a big enough bag to be folded over to trap the contents. Beating trays are particularly poor for caddis as they jump off the tray. Beating is successful if you beat into a net.
Caddis also light-trap in numbers. They are one of the first of the nocturnal insects to arrive so you can give up after an hour of true dark and miss very little – unlike the poor ‘mother’ who needs top be out all night. Caddis can also be caught in Malaise type of traps.
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Adults can be taken from the net using an aspirator or “Pooter”, or simply tubed. Be aware that many produce a dreadful phenolic smell that instinctively you feel cannot do any good in your lungs. Adults die quickly if immersed in 70% methylated spirits or isopropyl alcohol and are preserved at the same time.
Preserving samples of caddis
This is best done in a 70% solution of alcohol in water, either using industrial methylated spirits or isopropyl alcohol. There is a lot of water in a caddis case or larva so make sure you use enough alcohol solution to take that into account. I actually use 80% solution to take that into account in a small way but do not make it any stronger or you end up with things that are too stiff to manipulate easily under the microscope.
Summary – or procedure to adopt to get the maximum number of caddis species from a site.
Visibly scrutinize the site.
1.Look for overhanging bushes or ferns and beat them into the adult collecting net. The reason for starting with this procedure is that such vegetation is often disturbed during later collecting.
2. Use the viewing tube to look on stones and submerged wood. Overturn a few large stones to look under them too.
3. Bring ashore some larger stones and wood etc. and scrutinize them for caddis. Look for honorary rocks i.e. brick and old bicycles to search on them for caddis
4. Look for submerged roots and weed beds to work with a net.
5. Finally, when you no longer need to see into the habitat do the kick and swirl and rock scrubbing and bottom disturbance with a net work.
6. Then if you have a light-trap use it.
