HOMES AND GARDENS - INSECT BOXES

If more pieces of decaying wood, especially logs, were left around gardens, rather than being burned or shredded, it would surely be very beneficial for the natural control of so-called pests.

The same applies to insect boxes, which include those with cardboard tubes designed particularly for the Red Mason Bee (Osmia bicornis, formerly Osmia rufa), those made of wood with holes drilled into them, and those containing cut stems. One can make them at home if required by using pieces of log up to 20cm in length and drilling holes of varying diameter, or cutting bamboo stems and placing them in a secure container with a solid backing.

My first foray was in 2009 with a box made by the Oxford Bee Company and after no success that year 2010 was much better. I had added a box with stems and a drilled brick made by the German firm Schwegler and a drilled beech wood block which unfortunately failed to last the course beyond the end of 2011 due to splitting. Thirteen of the Oxford Bee Company tubes were nested in, and intriguingly while nine of these were done by Osmia bicornis, the remainder were completed by a female Ancistrocerus nigricornis (12mm).

This species is a Eumenid wasp and the quickest of that family to emerge, sometimes as early as February or March if the weather is favourable. This is only the females, who are impregnated after hatching in July or August and overwinter as adults before emerging in the spring to start the next generation.

Although pretty common in Surrey, Ancistrocerus nigricornis seemingly is in decline nationally and is even rare in the adjoining county of Kent. Over five days the wasp made three cells in each of four tubes in the box. Each cell was stocked with an average of six micromoth caterpillars which were caught in bursts of up to 40 minutes hunting; on one occasion six caterpillars were brought to the nest in 31 minutes. The usual prey are tortricids and with plenty of oaks nearby the wasp probably had plenty of victims to choose from.

The cells are separated by earth partitions, and the larvae consume the prey within one or two weeks. Females are in the inner cells and males in the outer. The wasp can determine the sex of each larva by laying fertilised eggs for females and unfertilised eggs for males. The fertilised eggs receive sperm as they go past the storage area (spermatheca); the unfertilised ones do not. Since the males have a shorter pupa period the adult wasps all tend to emerge at the same time. The completed nest is sealed with a plug of moist earth.

As a point of interest, Aculeata (stinging Hymenoptera) benefit from being able to inbreed closely, with progeny from the same nest of a solitary wasp or bee able to mate successfully without any negative consequences.

The proximity of the wasp to nesting Red Mason Bees (Osmia bicornis, 12mm) made for some amusing results when one or other went into the wrong tube, leading to a temporary face-off. Osmia bicornis is a smashing bee unless it happens to be burrowing into the mortar of your house. They look handsome with the reddish colouring and pollen carried underneath the abdomen and they are well suited by the range of flowers found in gardens. This particularly applies to fruit trees such apples, plums and pears, which as individuals they pollinate much more efficiently than individual honeybees. Honeybees rely on bulk though, with thousands of workers in each nest.

Osmia bicornis is active from late March to the start of July and the female makes around a dozen trips to collect pollen to provision each of the eight or so cells in the chosen nest site, which can be almost anywhere. The ones nesting in the bee box were certainly very busy. The pollen is mixed with nectar to nourish the egg laid in each cell. Cells are sealed with mud, as is the end of the tube when the bee has completed her work.

Although solitary in nesting, Osmia bicornis is gregarious and once a colony has started there is every chance it will develop since the bees which hatch in one place often nest there themselves. However, four of the nine burrows in the bee box in 2010 seemed to be parasitised.

One of the principal parasites is Sapyga quinquepunctata (12mm), a handsome wasp which isn't seen that often in the field but turns up most years in my garden. Females are much larger than males, which have a distinctive white mark on the face.

Other insects which are connected with Osmia bicornis include the parasitic fly Cacoxenus indagator (5mm), which can be abundant on occasions, and the spider beetle Ptinus sexpunctatus (5mm). The latter seems to eat detritus, including moribund larvae and dead bees (or sometimes wasps) rather than live larvae. Mites are also a problem with Osmia bicornis. Reverting to Ancistrocerus nigricornis, early in 2015 I reared six Amobia signata (5mm) flies from a nest completed by the wasp the year before.

Two solitary wasps which always nest in the logs in the garden took advantage of the insect box with cut stems made by Schwegler. Trypoxylon clavicerum (9mm), distinguished from the other species in the genus by the red on its forelegs, was present in significant numbers in the garden in 2010. Five cut stems in the insect box as well as several empty beetle burrows in logs were stocked by members of the species between May and August. The nests are sealed with mud.

One noticeable feature was the variety in size of prey, shown in the image above. Unlike the spider-hunting wasp Auplopus carbonarius, Trypoxylon species seem to leave the legs on, and since these can be quite long it presumably makes filling cells a tad inconvenient.

Psenulus pallipes (8mm) also hunts aphids and is a tremendous worker. In 2010 one female constructed two nests in stems between the end of June and the end of August and stocked them vigorously with aphids - there can be more than 200 prey per nest. Two more females nested in the same box in 2011.

The most interesting use of the insect boxes in 2010 was by the pretty Red Data Book bee Heriades truncorum (8mm), which is also on the Sandpit pages here. Although Common Ragwort is the usual source of pollen in the wild, this bee has been found in the garden every year since 2007 foraging on members of the Asteraceae (Compositae) family including Helenium. The family also includes such showy and popular genera as Aster, Cosmos, Dahlia, Gazania, Osteospermum, Rudbeckia and Zinnia so there is usually plenty of choice in gardens locally. The sole requirement for Heriades truncorum is that the Asteraceae flowers have to be yellow.

The species is unquestionably versatile, since in Britain females have been observed nesting in dead trees, fence posts, old logs, dead bramble stems, decaying wooden window frames, thatch, and fissures in the masonry of a house wall.

In mainland Europe the use of bee boxes by Heriades truncorum is well known. At least two females tried nesting in the garden boxes between July and September 2010, but in part because of the poor weather in August only two of the six nests were completed and sealed, using resin as always. Both were in cut stems.

The cells - up to ten - are also separated by resin and the speed at which the females gathered this, every five or six minutes, was impressive. In contrast, collection of pollen took at least eight minutes, probably because it would have come from more than one flower and needed packing evenly beneath the abdomen. Resin is usually packed into a ball for transportation but once the parcel, a massive one, had a definite 'tail'.

There was plenty of choice for resin nearby, with pines, fir trees and deciduous trees, any of which the species can use. Sealing the nest was a real labour of love since the female brought 11 loads of resin which she carefully worked into the last 5mm or so of the reed. Finally she covered the resin with fibre garnered from stems close to her own.

Interestingly the female who completed both nests started out by strenuously trying to enter a wooden hole only 2mm in diameter, much too small.

In 2011 I went for broke, adding boxes kindly provided by Robin Dean of the Red Beehive Company and Dr Adam Bates of Birmingham University - the latter had mainly cardboard tubes in it - plus two boxes I made myself containing bamboo canes. The results were tremendous. Thirty-five Osmia bicornis nests were completed, though the majority were 'got at' almost certainly by Great Spotted Woodpeckers or Great Tits, both well known as raiders of aculeate nests.

The 'Bates box' attracted two Ancistrocerus nigricornis, which completed six nests in April, using a good variety of caterpillar prey, some of which were larger than the wasps. The next generation of wasps emerged from these nests in July. An Ancistrocerus trifasciatus (12mm) completed four nests right by those of the Ancistrocerus nigricornis, one of which was visited by the parasitic ruby-tail wasp Chrysis ignita (10mm). The latter species also attacks Ancistrocerus nigricornis but the usual ruby-tail found taking advantage of that host is Chrysis terminata, from the Chrysis ignita group and only recently confirmed as a British species. It needs different tactics, overwintering as an adult like the female Ancistrocerus nigricornis after emerging in July or August.

A novelty in the 'Dean box' and in one of mine was two female Pemphredon lugubris (12mm) nesting in bamboo. This species uses dead wood and was very active as usual in some of the logs in the garden but bamboo canes are dead wood of a different type and offer good opportunities for this wasp since they have plenty of lining to work with. The boxes were also free of the attentions of social wasps, which were ever present gathering wood pulp at the logs.

The box with stems and the brick proved sensational. After no use was made of the brick in 2010 this time there were ten Osmia bicornis nests, one Trypoxylon clavicerum nest, one Osmia caerulescens nest and one Hylaeus communis nest completed. A female Symmorphus bifasciatus (12mm) also turned up to gather mud from an Osmia bicornis nest in the brick that had been broken into - the wasp was nesting in an elder stem within easy reach in the garden. The species returned in 2016, nesting in wood as before.

Osmia leaiana (10mm) is a common species in gardens and gathers pollen almost entirely from yellow composite flowers. There have been ten or more nests in insect boxes in the garden since 2013 and in 2014, 2015 and 2016 several individuals of the handsome and nationally scarce ruby-tail wasp Chrysura radians (10mm) spent a lot of time watching the nests and entering some to lay eggs.

Osmia caerulescens (Blue Carpenter Bee, 10mm) is very attractive and is often found in gardens in the south but they are nothing like so common as Osmia bicornis. The two using this box - a couple of nests were also completed in stems - seemed to take a very long time to stock the nests with pollen and to collect then chew the petals or leaves used to make partitions between the cells and close the nest. Even on sunny days they sometimes appeared only two or three times and the nests took up to three weeks to complete. Osmia bicornis can complete a nest in a matter of days though intriguingly one spent a whole day closing hers in bamboo with mud.

The most intriguing nester was Hylaeus communis (8mm), one of the Yellow-faced Bees which is common in gardens. In parts of the continent they have been known to be double-brooded for a long time but no proof had been found of this in Britain, for all the strong suspicions, given that the flight period runs from May to September. The female started nesting in the brick on 8 May and finished on 23 May when she sealed the exit. Proof came from the box in July when I saw a female emerging from the brick and found the old nest to be empty. The second brood completed eight nests in stems in the box but sadly all were broken into, probably by tiny parasitic chalcid wasps.

Heriades truncorum had an annus mirabilis in the stems, completing 33 nests and attracting six or seven of the rare cuckoo bee Stelis breviuscula (8mm). The latter spent lengthy periods checking out the stems, going into as many as they could to check the status, sometimes coming out with their faces covered in pollen. Oddly this activity was all in July with no sign of Stelis breviuscula in August even though the host was continuing to nest in numbers.

The Heriades truncorum nests were often in very close proximity and this perhaps contributed to several fights I saw, caused usually by a female with pollen returning to the wrong stem then being found there by the 'owner' when she returned. This is unlikely to be something which would happen in the wild so it raises the question of whether by trying to help species we may occasionally influence their behaviour in a negative way.

This looked to be the case with Trypoxylon clavicerum, which completed more than 30 nests in the stems between April and October and proved to be double-brooded, another first for Britain - in September I opened up a stem which had been filled in the spring and found it completely empty apart from residue of the mud partitions between the five cells. This species also nested in close proximity and there were arguments, even to the point of one female dismantling another's nest and leaving some of the spider prey, one with an egg on, dangling from the edge.

Perhaps the highlight though was the wasp Crossocerus megacephalus (8mm) nesting in the beech block. This is a species that has bred in the garden several times but seeing and photographing this female bringing various flies back to her nest, many of them the Soldierflies that form the habitual prey, was marvellous. Regrettably she died before completing her second nest alongside the first.

The success of the boxes has continued and in 2016 Heriades truncorum completed more than 200 nests while Osmia bicornis completed more than 400 and Osmia leaiana 13. One of our smallest bees Chelostoma campanularum (6mm), which takes pollen only from bellflowers, usually nests in wood but several utilised the cut reed alongside the Heriades truncorum. The wasps also did reasonably well in the reeds.

In passing, bees and wasps aren't the only invertebrates to use the boxes, with woodlice, ladybirds and spiders among the other taking advantage of a safe haven. Two spiders of note were a Pardosa species with an egg sac who sheltered in one of the cardboard tubes for several days, and a Nuctenea umbratica (15mm), typically associated with eaves, fences, tree trunks and bark, who spent at least a fortnight in another tube.

This species, known colloquially as the Walnut Orb-weaver Spider, constructs a web up to 70 cm in diameter in the evening and waits in the centre for prey through the night. Usually they hide during the day but this one seemed to relish being in the sun outside her tube. They can bite, causing itchiness and a burning sensation.

The Bees & Wasps in flight page has more images of the species shown here.

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.