A sinister visitor

 

My new bee house is covered in a wire mesh as protection against birds but it is no match for this predator.  This is a female ichneumonid wasp, a parasitoid of solitary bees, possibly Ephialtes manifestator, although ichneumonids aren't easy to identify.  I first saw this one with her very long ovipositor already through the mud seal on one of the completed red mason bee nests.  She was constantly twisting her body to manipulate the tip of the ovipositor by feel to penetrate one of the cells inside.  Once in she lays an egg which will hatch and the larva will devour the bee larva and all the stored pollen and nectar in the cell.  It will then metamorphose into a wasp and wait until next spring to emerge, along with the surviving bees.

At one stage the ovipositor was in up to the hilt (40mm or so) so it may have penetrated more than one cell inside.  The ichneumonid was already in position when I noticed it and it was over 75 minutes before it withdrew, showing extraordinary patience.

Then it was sniffing around the other cells, looking for another opportunity, bending its antennae like this as it probed the mud seal.

At one stage it was considering this blue mason bee nest but couldn't see what I could see, that the completed nest is only half full and the cells would have been out of reach.

The next day it was back, this time attacking a red mason bee nest in the observation section.

After selecting the target it withdrew the ovipositor from its sheath and very carefully probed the mud seal.

And after only two minutes it was through.

Then it spent another 59 minutes trying to get past the second wall but failed, and eventually gave up.

I had thought the empty chamber, which is often at the front of the nest, to be a defence against birds but it will be equally effective against this kind of attack.

There are lots of other parasites around the bee house.  Some, such as this Sapyga quinquepunctata, a parasitic wasp, sneak into an unfinished nest to lay an egg while the owner is away.

Ichneumonids wait until the nest is complete and the host larva is growing before they attack. Another one I see quite often is Gasteruption jaculator which is smaller than Ephialtes manifestator and has a shorter ovipositor, probably targeting small solitary wasps and bees.