Solitary bees

by Ted Benton

Overview

In Britain and Ireland there are about ten times more species of solitary bee than bumblebee and honeybee combined, yet the solitary bees tend to be ignored and we know much less about them. They are a fascinating, attractive and diverse group that can be found easily in a wide range of habitats, both urban and rural, and they are important as pollinators.

Solitary bees provides an introduction to the natural history, ecology and conservation of solitary bees, together with an easy-to-use key to genera.

Chapters cover: Diversity and recognition; Bee lives; Cuckoos in the nest; Bees and flowers; The conservation of solitary bees; Approaches to practical work; Keys to the genera of bees of the British Isles - Females and Males; and References and further reading.

Product Details

ISBN-13:	9781784270896
Publisher:	Pelagic Publishing
Publication date:	03/08/2017
Series:	Naturalists' Handbooks , #33
Sold by:	Barnes & Noble
Format:	eBook
Pages:	208
File size:	31 MB
Note:	This product may take a few minutes to download.

About the Author

Ted Benton is emeritus professor of sociology at University of Essex, where he has pioneered the integration of ecological understanding with social theory. He has been an active field naturalist since childhood, and is author or co-author of eight books on entomological topics, in addition to his academic publications and a recent book on Alfred Russel Wallace. His two books in the New Naturalist series (Bumblebees (2006) and Grasshoppers and Crickets (2012)) have both been highly praised. He is hon. President of Colchester Natural History Society, a founder member of the Red-Green Study Group and is involved in environmental campaigning.

Read an Excerpt

CHAPTER 1

Introduction

Everyone now knows at least two things about bees. First, that they provide 'free' services in pollinating a great many of our food crops. Second, that many of them are in steep decline. Thanks to the work of both scientists and conservation movements, these important messages have given bees a high profile in the public imagination. This book is an attempt to take the argument a bit further. The importance of bees as pollinators of a great range of food crops is undeniable. According to some estimates as much as one third of the food we eat is dependent on insect pollination – and bees are by a long way the most effective pollinators. Bee pollination is also important for many species of wild flowers, so, for those of us who love to walk through our few remaining flowery meadows, the bees give us spiritual as well as physical nourishment. But, as I hope to illustrate in this book, bees are also important in their own right: a source of endless fascination and admiration for the wonderful diversity and complexity of their myriad modes of life.

The question of declining bee populations is a much more complicated one. Much of the media coverage equates 'bees' with honeybees. In Britain this means just one species – the domesticated honeybee, Apis mellifera. It has been well publicised that beekeepers regularly suffer alarming losses of colonies to disease, most notably as a result of infestations of the Varroa mite. Of more international concern has been the phenomenon known as colony collapse disorder. The primary causes of these threats to honeybees are still subject to controversy, but whatever the explanation, the problem points to the risks posed by commercial reliance on just one bee species. Next in line, and very popular with the public, are the bumblebees. Like honeybees, the bumblebees are highly social, and are very effective as pollinators. Because of their unique methods of maintaining their body temperature above the ambient, they can forage earlier, later and in cooler conditions than many other bees. They provide a crucial supplementary pollination service, and are even bred commercially for this purpose. But there has been a great deal of alarm about bumblebee decline, too. The spread of intensive, industrialised agricultural systems, including use of neonicotinoid insecticides, has taken much of the blame for this. The majority of our bumblebee species do, indeed, seem to have declined drastically, although even the worst-affected species may be responding positively to conservation measures, such as agri-environmental schemes. However, a small number of species appear to be coping well with the environmental changes we are imposing on them. These species are often adapted to urban and suburban habitats, to domestic gardens, parks, roadside verges, flood defences and the like. Where these habitats are managed (intentionally or not) to provide a good range of nesting habitats and suitable flowers through from early spring into the autumn, the common bumblebee species seem to thrive.

The honeybee and bumblebees are well publicised and have their place not just in public understanding of their importance as pollinators (or providers of honey), but also in their cultural uses in children's literature, cartoon animations, and as icons of truly selfless social life. However, the rest of this book is devoted to the other bees. That is, the 225 or more species of wild bee that inhabit the British Isles, and which are neither bumblebees nor honeybees. These lesser-known bees are often seen, but only rarely noticed. Nevertheless, some are so familiar that only a brief reminder will call them to mind. One such is the amusingly named hairy-footed flower bee (Anthophora plumipes). In common with many of our wild bee species, this bee is more frequent in southern England and Wales, occurring more sparingly into northern England. It is especially common in gardens, and is one of the first bees to appear in the spring. The males emerge first. They are ginger-brown, and look quite like a small bumblebee. However, their behaviour is quite distinctive. They patrol regular routes around flower beds, or flowering shrubs, flying fast, and pausing occasionally to inspect flowers, such as cowslips, rosemary, Ceanothus or flowering currant. The point of this behaviour is to locate newly emerged females as they forage for nectar on the flowers, but in most years the males have some days to wait for their first opportunity to mate. Meanwhile, the males, too, need to visit flowers for nectar, and when they do so it is possible to see the reason for their name – a plume of long fine hairs trailing gracefully from their feet. When the females do emerge, they could easily be taken for a quite different species. They are covered in a fine coat of black hair, with a patch of bright yellow-orange hair on each hind leg. This looks superficially like the full pollen-basket of a small bumblebee, and it has a parallel function. The female collects pollen on these hairs (the scopa), and when she is observed at this, we know she has already established her first brood cell. This is constructed from compacted soil or other material, in a hole or crevice in an old wall, or exposed bank. Here she will prime the cell with pollen, mixed with some nectar, before laying a single egg, and sealing it.

Rather later in the year, tidy-minded gardeners might be disappointed to see neatly cut round or ovoid holes in the leaves of their prize roses. This is the work of the appropriately named leaf-cutter bees (Megachile species). However, this disappointment is a very small price to pay for the pleasure of sharing one's garden with these fascinating insects. It is a rare treat to watch the female cutting out the shape she needs, and flying off with it to line a brood cell. Soon she will return to the flower-bed to collect pollen among rows of stiff hair on the underside of her abdomen.

Towards the end of June, or early July, the males of another bee take up patrolling routes in the garden. These bees are dark brown, with pairs of yellow marks at the sides of the abdominal segments. The face has a bright yellow pattern, and there are silvery hairs on the feet. There are five small pointed projections at the rear of the abdomen. This is the wool-carder bee (Anthidium manicatum). The males patrol in a manner similar to the hairy-footed flower bee, but they are much more aggressive. Each male defends its own patch of flowers, diving at intruding insects – not just other males of its own species, but others, such as honeybees. When in attack mode it bends its abdomen forwards, so its spines become weapons. Again, the point of the patrolling is to locate potential mates, and the males can be seen to hover in front of clusters of flowers, apparently inspecting them for foraging females. When one is located, the male approach dispenses with formalities. He darts at the female, and, if she is slow off the mark, grabs her and mates with her. The females are much more discreet, and it is they who justify the common name of the species. They line their nest cells with 'wool' formed of finely cut plant hairs, which they snip from the leaves of plants such as lamb's ears (Stachys byzantina).

This tiny sample of our more familiar solitary bees gives just a hint at the diversity and fascination of the whole group. First, I should give a few words to explain the title of this book. The honeybees and bumblebees are the best known of the bees, and their complex social lives are widely recognised. Most of the bees discussed in this book are termed solitary because they do not have a separate non-reproductive caste of workers. Instead, the females make nests, provide a store of provisions for their offspring and lay their eggs, while the role of the males is generally limited to finding and mating with a female. However, for a number of reasons, but often simply because suitable nesting sites are highly localised, large numbers of females – sometimes into the thousands – may nest in close proximity to one another. These dense aggregations can give the appearance of sociality, and the bees certainly don't appear to be solitary! Still, in general, each female recognises her own nest entrance, and there is no overt cooperation between them. To make matters still more complicated, there are several species (some of which are included in this book) that have developed various degrees of social cooperation – possibly as an evolutionary option provided by aggregation in their nest sites. The social lives of some of these species provide interesting evidence bearing on the evolution of sociality. However, there is no simple term to cover the great diversity of bees occurring in the British Isles that are not bumblebees or honeybees. For convenience in this book I will refer to them all as solitary bees, just making it clear where necessary that a few are social.

As the above accounts of familiar species suggest, a local park or garden is a good place to begin to study bees. Some enthusiasts who provide artificial nest-sites as well as the right range of flowers have managed to invite over 100 species into their gardens. But beyond the garden, bees can be found in a great range of habitats – both urban and rural. The open places in woodland (glades, wide rides and edge zones), heaths, old grassland, chalk or limestone grassland, moors, banks, quarries, old walls, roadside verges, railway cuttings, the edges of footpaths, flood defences, sea cliffs and sand dunes all offer nesting and/or foraging resources for bees. Many species make their nests in burrows, and these species are most often found on loose, sandy soils, where the vegetation is sparse. Heather heaths, coastal dunes and worked-out sand and gravel pits are good places to look – especially where there are south-facing bare exposures. These conditions are frequently found in ex-industrial so-called brown-field sites, and some of these are among the richest sites of all, not just for bees but for other invertebrates, too, and for many scarce wild flowers. The value of such sites to wildlife conservation is all too frequently ignored by planners and developers, and many have been lost. Useful work can be done by amateurs in providing the evidence to publicise and defend these much-despised places.

1.1 What is a bee?

Most of us, most of the time, can just intuitively recognise an insect as a bee, a wasp, a hoverfly, or a member of some other group. However, it isn't always so easy to do, as there are some bees that look very much like wasps, and some members of other insect groups that have evolved to look like bees. In some cases there are reasons to think these similarities are not just coincidences. As many bees can sting, non-bees that look like bees, but cannot sting, may benefit by being protected from wary predators. Some of the best examples of this mimicry are found among the mimics of bumblebees, but some solitary bees have their mimics, too. So, it might be useful to know in more depth where the bees fit into the general scheme of insect classification, and how to separate them from their various lookalikes.

The bees, together with ants, wasps, horntails, sawflies, velvet ants, parasitic wasps and others, belong to the huge insect order, the Hymenoptera. Almost all species of Hymenoptera have wings, and these are usually transparent or, if tinted, still translucent – unlike, for example, the scale-covered wings of butterflies and moths, or the hard, shell-like modifications of the forewings of beetles. Unlike flies (Diptera - some of which superficially resemble bees), which have just one pair of wings, the hymenopterans have two. However, when an insect is at rest, or, perhaps, taking nectar from a flower, the wings are closed over its back, so it is not easy to tell if it has two pairs or just one. A useful clue in that situation is given by the shape of the head. Bees (and most other hymenopterans) tend to have relatively small compound eyes, situated at the sides of the head and separated by a distinct 'forehead'. In most flies, the head is dominated by very large compound eyes, with little or sometimes no space between them (as seen from above) (Fig. 1.1). Dragonflies and damselflies (Odonata) and mayflies (Ephemeroptera) differ in many ways from the Hymenoptera, but perhaps most obviously their wing-veins form dense networks, contrasting with the much simpler patterns formed by the wing-veins of the hymenopterans (Fig. 1.2).

The Hymenoptera comprises a huge diversity of insects, with numerous subdivisions. The first of these is between the Symphyta and the Apocrita. The Symphyta include the sawflies and horntails, and they differ from the members of the Apocrita in lacking the abrupt narrowing of the body, the 'waist', that characterises the bees, wasps and their allies. But even the Apocrita includes a very diverse range of insects, such as velvet ants, gall wasps, ruby-tailed wasps and parasitic ichneumon wasps, as well as the subgroup to which belong the bees, wasps and ants: the Aculeata.

The aculeates form a coherent grouping of insects, and many entomologists who study bees are also interested in their relatives, the ants and wasps. The Bees, Wasps and Ants Recording Society (BWARS) was set up to foster interest and gather knowledge of these insects in Britain and Ireland, and its website is an indispensable resource for any reader who wishes to take their study of them beyond the limitations of this short book.

But our focus here is on the bees. How do they differ from the ants and wasps? Most obviously, the bees are all furnished with two pairs of wings in the adult stage, whereas most ants are wingless. However, the reproductive castes of ants are winged, and they appear, often in huge numbers, as their nests mature. Like other winged hymenopterans, they have two pairs of wings. These ant castes, and, indeed, all ants, differ from bees in their bodily structure. The differences can be seen quite easily, but some explanation is needed. I mentioned above that the Apocrita (including the ants, bees and wasps) have a marked constriction around the middle of their bodies. This is commonly called the waist. The typical structure of an insect body comprises three main parts – head, thorax and abdomen. In the aculeates the waist appears to separate the thorax and abdomen. Unfortunately it is not so simple. In fact, the first segment of what would be the abdomen in other insects is fused with the rear of the thorax to form a structure called the propodeum. To the rear of this, the following segments of the abdomen at first narrow sharply, then widen out again towards the rear of the insect. In the ants, the narrowing of the waist is continued, involving the foremost one or two segments of the abdomen following the propodeum. This gives the appearance of a stalk between the (modified) thorax and the rest of the abdomen. This narrow stalk consists of one greatly narrowed segment (the petiole) in some groups of ants, or two (petiole and postpetiole) on others (the Myrmicinae). The remainder of the abdomen is called the gaster in the case of ants and this term is commonly used to refer to the visible segments of the abdomen in both wasps and bees, too. However, this is not strictly accurate. To avoid unnecessary technicalities the term thorax will be used in this book to refer to the fused middle part of the body, and the term abdomen to refer to the abdominal segments to the rear of the waist (i.e the equivalent of what some authors refer to as the gaster). The term gaster will be used when necessary to avoid confusion and is also used in the authoritative guide to the genera of bees of the British Isles presented in Chapter 8 (Fig. 1.3).

Bees lack the petiole, and the first segment of the (remainder of the) abdomen widens abruptly, to give a more compact impression of the body. In some species, the density of body-hairs is such that the waist is hidden. Many wasps have a more extended waist, the first one or two segments of the abdomen widening only gradually. These are readily distinguished from bees, but, unfortunately, not all wasps conform. In fact, solitary wasps are believed to be the evolutionary ancestors of bees and some groups, notably the sphecid wasps, are often difficult to distinguish from some groups of bees. One anatomical feature that does seem to distinguish the bees is the structure of the foot, or tarsus. In the bees the first segment of this (the basitarsus) is flattened and wider than the others. This feature is most marked in the case of bees such as those of the genus Andrena, whose females collect pollen on their hind legs. However, it is still clear in the wasp-like species of the genus Nomada, whose females do not collect pollen (Fig. 1.4). Other distinguishing features of bees either don't work in every case, or require some knowledge of the mode of life of the insect. In both wasps and bees the sexes are most easily distinguished by the number of segments in the antennae (12 in males, 13 in females), but in most species the females have stings – another useful character! Female bees usually (but not always) have some arrangement of hairs, either on their hind legs, under the abdomen or elsewhere, that are used for carrying pollen back to the nest. In general, bees tend to have relatively hairy, or furry bodies, whether male or female. With microscopic examination you can tell that these include many that are plumose – that is, they have fine branches along the length of the hair. Wasps are usually hairless, or have simple hairs on their bodies. Female wasps do not collect pollen, so do not have the hairy adaptations for collecting it.

(Continues…)

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Table of Contents

1 Introduction
2 Diversity and recognition
3 Bee lives
4 Cuckoos in the nest
5 Bees and flowers
6 The conservation of solitary bees
7 Approaches to practical work
8 Keys to the genera of bees of the British Isles
9 References and further reading
Index

Preface

In Britain and Ireland there are about ten times more species of solitary bee than bumblebee and honeybee combined, yet the solitary bees tend to be ignored and we know much less about them. However, they are a fascinating, attractive and diverse group that can be found easily in a wide range of habitats, both urban and rural, and they are important as pollinators. They are easy to study and are certainly no less interesting than bumblebees and honeybees. The main reason for the lack of awareness of solitary bees is probably that for over 100 years and until very recently there was no easily available guide to all the species. The publication in 2015 of a Field Guide to the Bees of Great Britain and Ireland by Falk and Lewington at last allowed anyone with an interest to make reliable identifications of solitary bees. However, identification of species can be daunting to the beginner. This Naturalist’s Handbook provides an introduction to the natural history, ecology and conservation of solitary bees, together with an easy-to-use key to genera, which can act as a stepping-stone to the use of a comprehensive key to species.

I hope that this book will encourage more people to study solitary bees. The more they are studied, the more we shall know about them and the better we shall be able to conserve them for the future. Surprisingly, ex-industrial brown-field sites can provide some of the best nesting sites for solitary bees, which means that solitary bees can be studied and protected, even in the centre of cities.

This Naturalist’s Handbook on solitary bees is a very welcome addition to the series, complementing the existing titles on bumblebees (no. 6), solitary wasps (no. 3) and ants (no. 24).

William D.J. Kirk, July 2016