Michael Viney responds to queries and observations on nature.
I got some large mussels from Clew Bay which were alive and closed. When I boiled them and they opened, there were tiny crabs inside two or three of them. Were the crabs living on the mussels or on the food that the mussels gathered?
Rosalind Davies, Newport, Co Mayo
They were pea crabs, Pinnotheres pisum, which live inside a number of mollusc shells, including mussels, and feed on the strings of food collected by their host.
Why do so many birds remain in Dublin during the winter, and start singing vigorously at 3am?
Anngret Simms, Sandymount, Dublin 4
The garden birds remain where there is food, and street lighting encourages them to sing. The birds here have also started the dawn chorus in January. They must know something we don't.