A  distinctive black and red or orange ground bug with an orange abdomen. 

Arocatus roeselii on Alders

You must state the tree speces on which the bug was found.  If this is not known/unclear, submit as genus only

Plane trees (Platanus sp.)

All year round.

Feeds on the seeds of plane, producing several generations before overwintering communally under bark. Flies readily in warm conditions, when the orange abdomen is conspicuous.

Found widely in the southern half of Britain.  A recent immigrant to the UK, first noted in 2007 and by the end of 2015 it had become abundant on Plane trees in parts of London. (ref:. British Bugs webpage for the combined species)

Not known. In 2024 there were no verified records from Plane trees.  

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