I use this technique for some of the tiniest British beetles: ptiliids and corylophids. The featherwing-beetle family (Ptiliidae) includes the smallest British beetle Nephanes titan and even the largest British ptiliid is only 1.2 mm. Dissection is useful for identification of the 6 British species of Orthoperus (Corylophidae) which range from 0.56 to 1.03 mm. These tiniest of beetles don’t have many fans and quite a few of even the most experienced coleopterists ignore them most or even all of the time. Dissecting such tiny beetles seems an outrageously difficult thing to attempt but Roger Booth demonstrated a technique on an Acrotrichis (Ptiliidae) at a BENHS workshop once which is actually quite simple.
1. With the beetle on its back, detach the abdomen.
2. Poke a pin into the abdominal cavity at the base.
3. Slide the abdomen up the pin until it splits along one side.
4. Remove the split abdomen from the pin, open it out and lift out the aedeagus or spermatheca.