My last entry ended with the masked bee completing her nest in a bee hotel, and the comment “all seems to have gone well.” But alas! 4 hours later a weird skinny insect drifted in to inspect the hotel.
The new arrival was a carrot wasp, so-called because some are known to favour carrot flowers as a food source. Carrot wasps (Gasteruption) are typically very long and skinny parasitoid wasps, with an equally long and skinny white-tipped ovipositor for egg-laying. Cruising around looking for bees’ nests is typical of their behaviour, and pretty soon this wasp was perched at the entrance to our masked bee’s nesting tube.
It was then that I discovered that I had been misled. That long white-tipped structure was not an ovipositor, just a cover or sheath for it. The real ovipositor was the brown needle sticking deep into the masked bee's nest, while the sheath was bent away from the nest tube. You can see this in the next photo.
After laying one or more eggs, the carrot wasp withdrew her ovipositor and began to press it back into its sheath. Here it’s almost pressed back in.
A second later the true ovipositor was completely hidden once more.
The wasp then cruised off, leaving her eggs to hatch and develop in the masked bee’s nest. The larval development process varies between parasitoid wasp species. In the case of Gasteruption wasps each egg hatches rapidly into a larva with oversize jaws, which it uses to destroy the host bee’s eggs. Then at subsequent stages of its development, the wasp larva has more normal size jaws which it uses to feeds on the food supply left for the host bee’s larvae.
The start of this entry refers to a “weird skinny insect” which I think is apt. This close-up of another Gasteruption wasp shows what I mean.