The mysterious aquatic leaf beetle Macroplea pubipennis has become quite familiar to us these last two summers. Not a lot is known about these beetles. Two years ago, we didn’t even know they existed in Sweden and they were known to occur only in Finland and China (of all places).
As observation sites in the Swedish Bothnian Bay have now added up to a total of 7, and we have seen hundreds of individual beetles, we have learned a lot about where they thrive. We have also learned a bit about other species of Macroplea. We would like to share to others what we have learned. So this is how you can find Macroplea pubipennis in the Bothnian Bay:
How to find macroplea pubipennis!
1.What we have learned about this beetle is that it likes semi-sheltered bays and rarely ventures far from the reed edge. Almost all our observations have been just within a few metres from the reed edge, as other species of Macroplea (M. appendiculata and mutica) also can be found deeper and in the middle of bays. For some reason bulrush (Schoenoplectus sp.) will not do and it has to be common reed (Phragmites australis).
2. Most of the beetleshave been found on perfoliate pondweed (Potamogeton perfoliatus), which is odd because it has before been known to prefer sago pondweed (Stuckenia pectinata) or watermilfoils (Myriophyllum sp.). These beetles live their larvae and pupa stages in the roots of aquatic plants and in july-august emerge to the open as adults. Perfoliate pondweed are hard to yank up with their roots intact so the easiest way to find these beetles is to snorkel and calmly look around for the grown individuals looking for mates and host plants.
3. You have to be extra calm and careful when looking for these animals. Their color is often similar to the background (as on the video) and the small hairs all over their bodies collect sediment, making them blend in even better. The best place to find them are places with only a little of vegetation, preferably perfoliate pondweed. Look for small dark or light dots (depending on if you see their back or stomach), tiny details or small movement. If you are lucky enough to see one Macroplea pubipennis, you are likely to see many.
Written by Petra Pohjola, County Administrative Board of Norrbotten