The scarcest wasp found in my garden is a female dryinid Dryinus collaris (7mm) in May 2015. Presumably brought in on clothing after I had been working on some shrubs, it was spotted walking up the kitchen window. All dryinids are elusive but this one is particularly rare across Europe. Mine was only the eighth record in Britain, starting in the 1850s. Most records have been this century, so possibly it is increasing. This is a parasitoid, which uses its flanged fore-tarsi to grasp the host and lay an egg that develops inside a sac on the outside of the victim. Nymphs used are of the ivy-eating planthopper Issus coleoptratus, as can be seen in the image alongside. This bug is common and it is conceivable that more searches would reveal more specimens of the wasp.
Moving on to more typical wasps, placing some decaying logs up to a couple of metres high in a sunny spot in a garden can provide excellent opportunities for the 'aerial' nesters among our bees and wasps. Beech is the best wood, since it has exactly the right texture; willow is also good and oak and birch (particularly if affected by Birch Polypore fungus) can be productive. In addition, insect boxes, including those made by the German company Schwegler, tend to increase the activity splendidly and the species which have nested in those (some of which have also nested in the logs) are shown on the Insect Boxes page. Images of aerial activity are on the Bees & Wasps in flight page.
The habitat of decayed wood is, of course, ephemeral, since once the substance is suitable for burrowing, it has only a relatively short time to go before falling apart. That's one reason why sensible conservation practices in woodland, allowing dead wood to decay in its own time unless there is a definite danger to people, are vital, since they ensure continuity.
In the space of ten years about 50 logs I have placed near the greenhouse and against hedges in the garden have been well utilised both by those species which use former beetle burrows and those which do their own digging. One highlight in late summer 2015 was watching 12 female Ectemnius cephalotes (15mm) and two Ectemnius cavifrons (15mm) bringing hundreds of flies back to their nests in a standing birch log.
Both species are in flight from June to October or even November. Ectemnius cephalotes, which nests communally, catches a wide variety of flies, including hoverflies, blowflies, muscid flies and flesh-flies. Ectemnius cavifrons, which can have two broods, catches hoverflies by preference but in 2015 both also caught the soldierfly Sargus bipunctatus. The burrows can contain ten or more cells in a branched system, which presumably does little for the stability of the log. Each cell has one egg and the larva has up to 12 flies to feed on.
Two species of parasitic fly kept checking out the nests of both species, and laid eggs. They are the anthomyiid flies Eustalomyia festiva (10mm) and Eustalomyia hilaris (8mm). The latter is nationally scarce.
By accident, many solitary wasps do good work for gardeners by catching plenty of species regarded as pests as prey for their progeny, especially aphids. In the garden in 2010 and 2011 around 20 of the so-called Mournful Wasp Pemphredon lugubris (up to 12mm) nested in the logs and two in bamboo canes.
A female of this species can put up to 40 good-sized aphids in each cell in its branched nest system in decayed wood. The cells are constructed in rows. There are eight species in the genus in Britain, and they look very similar. Both Pemphredon inornata (8mm) and the scarce Pemphredon morio (7mm) nest in the garden. The Red Data Book species Pemphredon rugifera is another from the genus. All are shown in the Woodland pages of this website.
Nest, or entrance, sharing is not common with solitary wasps - an exception is Ectemnius cephalotes, shown on the Dead Wood page of the Woodland & Hedgerow section - but usurpation is found much more often. In October 2007 (pretty late for starting a nest) an Ectemnius continuus female took over a Pemphredon lugubris burrow. The latter, who had more reason than most to be mournful, tried to keep possession but as a smaller species there was no chance of her succeeding.
Given the greater size of prey Ectemnius continuus catches - the picture above shows the female usurper with one of her 'catch' - and the fact that they have one cell with up to eight flies per 'branch', the nest required considerable extra excavation, the results of some of which are shown above. Despite the late start, the female completed her nest.
Various other species have nested in the logs. The most exciting personally, at least when I succeeded in catching it with the camera, is the spider-hunting wasp Dipogon subintermedius. This species habitually uses old beetle burrows for its nest and catches exclusively Segestria senoculata, a fairly common spider often found under bark.Dipogon subintermedius had been recorded in the garden several times but never with prey until 2016, when two females nesting 20 metres apart proceeded to catch spiders with within half an hour of each other. One nested in dead wood, as usual, but the other utilised a bamboo cane.
The winners in sheer numbers in the logs include Stigmus solskyi and Stigmus pendulus (6mm), which also prey on aphids. The latter is expanding its range, having first been identified in Britain in 1986.
Crossocerus annulipes (7mm) is a decayed-wood burrower preying on Hemiptera and at least eight nested in the logs in 2010. It is in flight from June to October and the nest can contain 20 cells with anything up to 25 prey items in each, a formidable total. The nests are branched and this can involve a significant amount of woodwork. The female who did the drilling pictured above in 2010 was stocking a nest as late as the second week of October and on one warm day she managed to take 18 prey items in an hour. The next year a female was still catching prey on 26 October and attending her nest on 29th.
From the same genus, and the same size, Crossocerus distinguendus uses aphids or Diptera to stock its nest which can be in a fairly wide range of sunny locations including sand or gravel slopes, vertical banks, decaying timber or in the soft mortar of old walls.
There were at least four Crossocerus distinguendus females nesting in the logs in 2010 and although officially this species is nationally scarce that assessment must be questionable. They used to be restricted to the south-east of England, especially Kent, but appear to be expanding their range, having been found in such widely-separated counties as Somerset, Shropshire and Yorkshire. Clearly a species that is doing pretty well.
Mimumesa dahlbomi (7mm) deals with Homopteran bugs and is fairly common. Rhopalum clavipes (7mm) can take a wide variety of prey, including Diptera, though in Britain Psocidae (book lice) and Psyllidae tend to be used as with the female shown above heading for her nest.
This is a widespread species seen at any stage from spring to autumn and despite the books stating that they usually nest in plant stems, at least three nested in one of the logs in the garden in 2007, including one in September and October. She was a tremendous huntress, catching an average of five prey items an hour for the two afternoons I watched her.
From the same genus and also common is Rhopalum coarctatum (7mm). This species uses similar locations and can have very long nests, up to 29 cells, though the average is half a dozen. Interestingly, old nests sometimes are re-used, quite possibly by the generation which emerged from them. Males, as in the image, have colourful legs and antennae.
The Passaloecus genus tends to have pale colouring on the mandibles, catch aphids and be in flight from May to September, nesting in pithy stems or old beetle borings. They are all of similar dimensions, about 6mm long, and the three shown here, all of which nest in the garden, are relatively common. Passaloecus corniger is perhaps the most interesting as it often steals prey from other wasps. Passaloecus gracilis and Passaloecus singularis are not noted for doing this to the same extent if at all. The use of resin to make partitions in the nest and combination of resin and stones to effect closure is standard.
Spilomena beata was one of the most interesting sightings during 2010, with two males and one female turning up on one of the logs. At only 2.5mm or so these were the smallest solitary wasps I've ever come across, and indeed they are the smallest in Britain. There are four species nationally, all catching thrips or possibly aphids and nesting in stems or beetle holes. Males uniformly have much brighter markings, chiefly on the face as the yellow on the pictured wasp confirms. In 2015 the commonest of the quartet, Spilomena troglodytes (3mm), nested in a beetle hole in an apple tree.
Pseudomalus violaceus (7mm) is a cuckoo wasp which preys on Pemphredon and Passaloecus species among others. Eggs are laid in the cells with the resulting larvae eating the food store of the host. This is a scarce species.
Images © Jeremy Early. All rights reserved.
In 2013 I published My Side of the Fence - the Natural History of a Surrey Garden. Details may be found, and orders placed, via this hyperlink My Side of the Fence. In November 2015 Surrey Wildlife Trust published the atlas Soldierflies, their allies and Conopidae of Surrey, jointly written by David Baldock and me. Details are on this web page: Atlas.