Easy to spot, six clearly separated red spots and black antenna tips. But be careful it is very similar to the Z. transalpina.

The red spots on the Z. transalpina are a little smaller and further away from each other than the Z. filipendulae, but that is not enough to identify it. On the forewing undersides of the Z. transalpina the spots are grown together, this is not the case with Z. filipendulae. The tip of the Z. transalpina antennas are yellow in contrast to Z. filipendulaes black tips.

There is another species which could be confused with Z. filipendulae and that is the Z. angelicae. The number of spots vary from 5 to 6, but the antenna tips are always clearly white.

More help here: http://www.lepiforum.de/lepiwiki.pl?Zygaenidae