Lygaeus equestris is a red and black seed bug measuring approximately 10 mm - 13.5 mm. 
The head is black with a red front which distinguishes it from other similar species. 
However, Lygaeus equestris is very similar to Lygaeus simulans and the two cannot be reliably distinguished from photographs. 
Lygaeus equestris occurs throughout Europe (and further east), but if you see one in western Europe, it is Lygaeus equestris. 
Lygaeus simulans occurs in southern and central Europe and especially eastern Europe and further east to Mongolia and China.
This little bug that I found in Bulgaria is either Lygaeus equestris or Lygaeus simulans.

The adult Lygaeus equestris/simulans also looks quite similar to Spilostethus pandurus but the red and black pattern on the shields is slightly different.

Like other Lygaeidae, Lygaeus equestris has an annual life cycle consisting of an egg followed by five successive nymphal stages before becoming an adult.

An adult. Melnik, Bulgaria, 28 July 2017