There are several species of Ruby-tailed wasps in the UK. The head and thorax are a dazzling greenish-blue, and the abdomen is a firey red. In bright sunlight the vivid metallic colours of their bodies appear very jewel-like.
Ruby-tailed wasps lay their eggs in the nests of other solitary bees and wasps. When they find a possible nest to lay their eggs they checkout the entrance to make sure no one is home. If they are unlucky and the owner is home they are well equipped to defend themselves with tough body cuticle to protect them from stings. Also the underside of their abdomen is concave which enables them to curl up into a ball.
If no one is home, they check to see the nest is well stocked with food, and then they reverse in and lay their eggs. When the eggs hatch, the emerging larvae eat the host bee or wasp larvae. For this reason they are sometimes called ‘Cuckoo Wasps’. They remain in the nest until they are fully developed and then emerge the following spring as adult wasps.