What are these structures on this fence post out in Phase 1. The post is in the water, about 1m out from the edge of the bank and there are up to 15 groups of them on the post. The length of the top group is about 3cm and the width is 0.5cm. Answer to follow next week....
Did anyone have a guess at this one? A change from galls this time, the structures that you see in the photos are alder fly, or Sialis lutaria, eggs. Alder flies are medium sized brown/black coloured insects, up to around 25mm wingspan and belonging to the Order Megaloptera. There are three species in the UK, of which Sialis lutaria is the only common and widespread one. Until fairly recently they were thought to be closely related to the lacewings and were grouped in the same Order, the Neuroptera, however they have now been placed in their own Order, within the larger group Neuropterida - which also includes the lacewings, snake flies and the antlion.
The eggs are laid in May and June, during the relatively brief flight period of the imago (adult) insects, which live in this stage for only 2-3 days. On hatching, the larvae will fall into the water, where they will spend their larval stage. They have strong, powerful jaws are are predatory, feeding on insects and other invertebrates. It takes up to two years for an alder fly larva to fully develop, at which time it migrates out of the water and into nearby vegetation or loose soil, where it pupates. The imago insects emerge after 2-3 weeks.