Eight isopods, of either stonewort or reed ecotype, were placed together with a single damselfly larva in an open plastic jar with diameter of 10 cm with no substrate. After 24 h the damselfly larva was removed. Each damselfly larva was used twice, once with the reed ecotype and once with the stonewort ecotype.

To examine effects of substrate and isopod ecotype on survival when exposed to damselfly larvae, 40 isopods of the same ecotype were put in a 1 L aquarium together with three damselflies.

The substrate was a layer of either reed. In the reed substrate all stem pieces where the isopods could hide inside were removed.  

After four days the trial was done and the isopods picked out from the substrate.

A 7,5x14x5 cm container were put in a 17x14,5x5 cm container. The bigger container was filled with a layer of light sand and the smaller one with a layer of black sand for the reed substrate and light sand for the stonewort substrate. The amount substrate in the small container was just enough to cover the bottom and the surrounding bigger container was filled with the same type of substrate as the small container. 

25 isopods were placed in the small container. The set up were then placed in a big aquarium. In the aquarium there were 5-6 perch (Perca fluviatilis ) that had learned to associate the set up with food.

The trial was observed the whole time and when the perch had done 13 seemingly successfull attacks the trial was finished and the container removed from the aquarium. The length of a trial varied from one to four minutes.

The isopods were photographed before and after the trials and the program ImageJ (downloaded at http://rsbweb.nih.gov/ij/) was used to measure the length. The length was measured as on the picture to the left.

For each group of isopods the mean length was determined both before and after and then compared to detect the effects the predators had on it.