Ecology

Social Aspect of the Aculeates

Social insects include some species of the aculeate hymenoptera and the termites (Isoptera).The social aspect of the bees, wasps and ants has been the subject of human curiosity for over 2000 years; the first documented observations coming from Aristotle's observations in the third century B.C.

There are ten species of social wasp which have been recorded within the UK and one, Polistes dominulus, is almost certainly a vagrant species. Probably the most stunning of these is the Hornet (Vespa crabro), one the largest British insects and definitely one of the most feared. It is in fact, probably the most docile of the social wasps and tends not to be particularly aggressive. The remaining species are all superficially similar and are often termed as the 'common wasp' although this could actually be any one of the nine species. These now include a couple of relatively new arrivals to the UK. Having appeared in the last two decades, these have tended to spread rapidly northwards over successive years.

Of the social bees, there is one native honey bee (Apis mellifera) and a further 27 bumble bees. The indigenous honeybee has been bred by beekeepers to produce strains that are both docile and produce plentiful amounts of honey. Honeybee nests can survive for very long periods of time and the queens and workers tend to overwinter by feeding on excess honey. The bumblebees have a similar lifestyle but do not overwinter because they do not produce enough honey for overwintering. Instead, an old colony dies but freshly mated queens hibernate over the winter emerging in early spring to start colony building all over again.

There are also a number of eusocial species amongst the solitary bees. These include certain Halictus spp. and Andrena spp. in the UK. Eusocial species tend to share the same nest but there is generally little or no cooperation between the females.

Nests and Nesting Behaviour

One of the key aspects about the aculeate hymenoptera is the need for a specific nesting site. In the case of many of the bees and wasps, food (pollen for bees and arthropod prey items for wasps) is collected and stored in these nesting areas to be later consumed by the larvae. Parasitic and 'cuckoo' species, although not constructing a nest of their own, still require the nests of other hymenoptera which they exploit. There are only a few species of aculeates in the UK that do not build their own nests or require the nests of others to survive.

Most bees and wasps are miners and burrow in the ground. In temperate climates about 70% of the nest building species are ground nesting, often favouring south-facing banks and cliffs, unstable slopes and field paths; particularly when bare or sparsely vegetated (Jones and Munn 1998).

There are, however, other species which nest in pre-existing cavities in cliffs, trees and very often in man-made structures. Old beetle borings and exit holes are also often used in fence posts and old trees. Another useful nesting site utilised by such species are hollow stems of brambles, umbellifers and other plants. There are also a few species in the UK that construct their nests. The most notable of these is the potter wasp (Eumenes coarctatus), which builds vase-like nests on rocks and plants.

Perhaps some of the better known nests are those within brick and mortar. These 'masonry bees' often dig nests into old and poor quality concrete in houses and other structures. Potter wasps and other solitary wasps species will also often utilise cavities in walls for nests. House walls, especially old south facing ones, can be a very profitable place to search for Aculeate Hymenoptera.

Other nesting materials are also often needed, dependant on the particular species. For instance, the wool carder bee (Anthidium manicatum) lines and partitions its brood cells with the hairs gathered from the leaves of lamb's ear and mullein whereas the red mason bee (Osmia rufa) partitions them with a mud clay.

Food and the Provision of Nests

In the UK, all bees tend to stock their nests with pollen whereas wasps stock their nests with arthropod prey items. One of the main reasons for there being a high number of different types of bees and wasps is the degree to which they specialise on specific food items. Bees can collect pollen from a variety of different plants (polylectic), or they are specialists, taking nectar from only one, or a few closely related species (oligolectic). There is also a high degree of variation between the flight times of different species; some are spring fliers, others are found on the wing only in mid or late summer.

All the wasps also tend to specialise to a certain degree. Some species may take flies, whilst others will only collect large hairless caterpillars or spiders. Other species show a higher degree of specialisation; Symmorphus mutinensis preys only on the beetle, Phyllodecta vulgatissima whereas the Bee-wolf (Philanthus triangulum) preys chiefly on honey bees.

Parasitism, Parasitoids and Cuckoo Species

There are a large number of species in the aculeate hymenoptera that show some degree of parasitism. This parasitism is often directed against the young larval stages of other species rather than the adults. The parasites involved tend to enter the nests of host species when the adults are away collecting food. The parasite will then lay its eggs on or near any foodstuff collected by the bee or wasp and then make its escape. This egg hatches quickly and the young parasitic larvae kills (and often eats) the host larvae as well as eating the foodstuff collected by the host adult. These parasitic bees and wasps are often quite specific. Nomad bees (Nomada spp.) are often specific to one or a handful of Andrena species; Sphecodes spp. generally attack sweat bees (Lassioglossum spp.) and rubytails (Chrysididae) are often associated with potter wasps.

Aculeates as Indicators

Aculeates are considered to be a very useful group to indicate habitat quality (Archer 1998, Jones and Munn 1998). Most of the bees and wasps generally require a complex of different habitats and micro-habitats that contain different resources. These resources will include nesting sites (dead wood or bare exposed ground) as well as other habitats containing nectar and pollen sources. There may also be further requirements such as nest materials. Such different resources are often only found in traditional countryside patterns (Kirby 1995) and the presence therefore of a large number of aculeate species within a specific area is often a good indicator of micro-habitat diversity and structural diversity. In many areas these countryside patterns have given way to intensive agriculture that contains little diversity. Because of this many species show a very restricted distribution and over 50% of the aculeates species on the national list are now considered to be under threat (Archer 1998).