Wasps in the Bee Hotel!

28th August 2014

I've been very pleased with activity in my garden "bee-hotel". I designed it originally, to attract Red Mason Bees (Osmia bicornis). It's been very successful at that but once Osmia nesting activity reduces as their season comes to an end, it's important to be able to attract different species.

It's usual to see a collection of bee parasites attracted to these structures. Parasites include several wasp (and bee) species. There are non-parasitic wasp species though, that will nest in these structures if appropriate "accommodation" is provided. The first image here shows an Ectemnius wasp that was using an empty hole to "roost" overnight.

Holes of 6-8mm diameter are good for attracting mason bees. I've recently started adding smaller holes though, in the 2-4mm range. These have been successful in attracting a range of small, nesting wasps and in the last post, I described some Passaloecus aphid-hunting wasps that had been active. These seal the nest holes with resin collected from trees. Here, a Passaloecus nest is being parasitised by what looks (to me) like an ichneumon wasp. The problem is, these "little black jobs" are very difficult for the amateur to differentiate. I hope that I'll improve as I continue to monitor them!

Sometimes, an individual wasp's behavior will give clues to its identity. I watched this one provisioning its nest with small spiders. It would make repeated excursions, returning each time with a paralysed spider held between its front legs. These are used to provision its brood chambers. The individual chambers and the entrance to the hole are sealed with mud. In the UK, these small, black spider-hunting wasps that use mud for nest building and have elongated abdomens are likely to be Trypoxylon species. I'm reasonably confident that this is one of those.

I spend an inordinate amount of time observing these fascinating little creatures. Sometimes this pays off with a decent photograph or with observing an interesting aspect of behaviour. This wasp was returning with resin balls to seal its nest and moulding them into position with its mandibles. It would then disappear into an empty, adjacent hole before returning back to the activity. On close inspection with a hand-lens I could see that it was reinforcing the resin seal with fragments of wood. It would appear that this behaviour has not been documented in the UK before! It's been suggested (from the photograph) that this could be Passaloecus or Pemphredon. An entomologist friend has agreed to have a look.

It's clear that providing a good seal to the nest is important, when parasitic species are looking to lay their own eggs in there. But there is also the risk that all the activity undertaken to provision a nest can be lost to simple nest stealing. I watched fascinated as this little wasp carefully removed the resin from this recently-sealed nest and then one-by-one, removed the aphids stored there and flew off with them! In the UK, the wasp Passaloecus corniger is known to exhibit this nest-stealing behaviour. I think that this, by its generally appearance, is likely to be that species.

Always interesting to observe is the preposterous-looking parasitic wasp Gasteruption jaculator. Quite large and with a very spindly appearance, this seems to have been a good year for them. I've seen lots at the bee-hotel; investigating holes and then choosing one in which to oviposit. She positions herself over the hole, unsheathes her ovipositor and then inserts it into the hole. Sometimes, they reverse into the hole and disappear totally down inside; presumably to parasitise deeper brood-cells. They appear so fragile that it surprises me that they re-appear still in perfect condition. A remarkable wasp, well-adapted to its parasitic lifestyle.

If you have Red Mason Bee nests then before long, they're going to be visited by this parasitic chalcid wasp Monodontomerus obscurus. It's a small wasp (3-4mm) with a green iridescence, red eyes and an ovipositor about the same length as the abdomen. Here is a female investigating a Red Mason Bee nest. Apparently, the wasp lays its eggs into the developing host bee cocoons. The wasp larvae then consume the developing bees, killing them. Parasites that kill their hosts are termed parasitoids.

Here's another temporary visitor to the "hotel". I saw a few of these appearing out of empty holes in the mornings, but apparently not nesting there. The rather angular structure of the eyes and the "thickened" areas on the forelegs, suggest that this may be one of the Crossocerus wasps. There are over twenty species in the UK, some nesting in existing holes in wood (old beetle holes etc) and some in the ground.

Smaller holes not only attract little wasps, but also the smaller species of bees like this female Yellow-faced (Hylaeus) Bee. Hylaeus are small, dark, wasp-like and virtually hairless bees. We have around a dozen species in the UK, most with some yellow or white markings on the face (and other parts of the body). Because they have no pollen-collecting hairs, it was thought in the past that they must be cleptoparasitic "cuckoo" bees that lay their eggs in nests provisioned by different bee species. They do in fact, carry nectar and pollen internally in their crops. This is regurgitated into the brood cells as food for their larvae.

Hylaeus bees are also interesting in that they secrete a special substance (via their salivary glands I understand), to line and seal their nests. This substance dries into a cellophane-like material. Here a female applies a layer of this material via a series of "licks".

So, I shall definitely be attempting to attract more solitary wasps next year, by adding blocks and logs drilled with smaller-diameter holes. Perhaps too, I should also drop the "bee-hotel" description in favour of "hymenopteran hotel". These industrious insects are fascinating to observe and easy to attract into the garden. They certainly keep me occupied!

[Click on any small image for a larger version]


Photo comment By Lucy Corrander: It's fascinating. I hadn't a clue about all these wasps. And such fine differentiations. I've put a link to this post on my 'Identifying Things Page' on my blog, Loose and Leafy. Hope this is ok.
Photo comment By Africa Gomez: Stunning photographs and info Ed. I really enjoy this post and look forward to new visitors to the bee hotel."

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