A distinctive black and red seed-eating bug found on Alders.

Arocatus longiceps. 

You must state the tree species on which the bug was found.  If this is not known or uncertain, submit record as genus only

Alder trees

Can be found widely in the southern half of Britain (ref.: British Bugs webpage for the combined species)

not known

https://www.britishbugs.org.uk/heteroptera/Lygaeidae/Arocatus_longiceps.html

The UK Species Inventory lists 2 separate species (A roeselii and A longiceps), although the British Bugs webpage states that it is more probable that these are the same species, but that the two names may still used to distinguish between alder-feeding and plane-feeding individuals.   We have therefore decided to maintain the two separate species, with an option to submit as genus only if the host-tree is not certain.