No interactions present.
how large was this beast? I can't see much detail, but the elytra look quite convex, which is usual for Bradycellus whereas Acupalpus are generally very flat. The sizes overlap, but the commoner Acupalpus are 2.5-4mm, whereas two common Bradycellus (which typically have a rather small pronotum compared with the elytra, like yours), are 3.8-4.3 and 4.5-5.2mm.
...at ≈3.5 mm was my first thought. Also it being tapped from moss not to far from a woodland marsh nearly had me convinced, but to many look alikes.
Now you saying the elytra look quite convex has me thinking that you are closer with Bradycellus, argh!!!
An iSpot Project- HELP WITH IDS - UK & Ireland Community - PLANTS
Lat/Lng: 53.2055, -0.5631
OS grid ref: SK960685
Backies woods, Boultham Moor, Lincoln. Also my garden