A wasp with a strange-looking body

I wonder what nature was up to when it evolved this wasp with a very elongated connector between the thorax and abdomen. Perhaps the purpose is to improve balance in flight? The wasp is about 3/4" long from head to abdomen, excluding the antennae. 

Shooting info – filmed in natural habitat at Bued River, La Union, Philippines, on January 18, 2018, Sony RX10 Mark IV + Uniqball UBH45 + Manfrotto 455B tripod, 600 mm (equiv.), f/5.6, ISO 100, 1/60 sec, manual exposure in available light, Steadyshot off, 4K/29.97p capture processed to 1920 x 800/23.976p (cinematic 2.4:1 aspect ratio). 

Music – “Sneaky Snitch” by Kevin MacLeod, incompetech.com (royalty-free).