We are trying to follow how a small litter-shredding caddisfly, Lepidostoma, finds leaf litter in streams. The larvae live in portable cases made of sand grains, so we should be able to mark animals for recapture by painting something on the case without poisoning the larva. Everything we have tried so far has not persisted long enough in the field. The larvae are very small (5-8 mm x 1-2 mm); we need only make a mark in a contrasting colour, not a specific number or tag. The marker must be visible, non-toxic, fast-drying (the animals can only be removed from water for a few minutes) and must persist in fast-running water for at least a week. Our best so far, oddly, has been red-coloured permanent markers. Any suggestions?
(Obviously these may interfere with the predator-prey interactions etc.) but you could use a permanent marker they use for cars? http://www.amazon.co.uk/White-Permanent-Waterproof-Marker-Drying/dp/B008MF6VGC
or there are UV paints that could work (which my have less of an impact on predator behaviour) http://www.amazon.co.uk/Compact-Pro-Permanent-Ultraviolet-Marker/dp/B0019SLP60 or http://www.nissenmarkers.com/product/ultraviolet/
Have you tried rearing them for a while in red garnet sand (or whatever color you can get your hands on) so that they self mark by adding a ring of red grains to their cases? I raised Limnephilis larvae years ago with match sticks in the tank. They happily added the sticks to their cases.
Thank you both for these useful suggestions. If I can get my hands on those permanent waterproof markers, they look like they might do the trick. I'm not too concerned about predator losses because the experiments are short-term (~ 1 week) and we are trying to see how far the larvae move about, not survival or population density. Rearing the animals in coloured sand is a cool idea, and it should work. We would have to start at the beginning of the field season (April) when the Lepidostoma are abundant but before they diapause or pupate later in summer. Maybe I'll give that a try next year.
Thanks for your help.
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