Insect Diversity Conservation

  • Michael J. Samways
Cambridge University Press: 2005. 342 pp. £30, $55 (pbk); £60, $110 (hbk) 0521789478, 0521783380 | ISBN: 0-521-78947-8

We really needed this book ten years ago when it would have illuminated an urgent but largely uninvestigated challenge of conservation biology. We have long been aware that the great bulk of the mass extinction currently under way is made up of insects, yet we have had only a meagre grasp of the details.

We have ‘guesstimated’ that 80% of the roughly 10 million species on the planet are insects. Yet we know so little about them that we haven't even located the main concentrations of insects (although one strong contender is the canopies of tropical forests). We know next to nothing about their natural histories or other key characteristics. And most important, we have only vague clues about their conservation status: how many species should be classified as threatened? Are species being eliminated at rates matching those for mammals and birds — that is, hundreds or even thousands of times faster than before modern humans appeared? All these questions are addressed in this compendious book.

It's true that a few taxa are well documented, notably butterflies (about 20,000 species), ants (8,000), dragonflies (6,000) and tiger beetles (25,000). But these total only some 60,000, and we cannot say how far they serve as indicator species to throw light on the rest. Fortunately, we can gain some insight by drawing on the congruence relationships of insects with plants. If we accept (gulp) that there are at least 300,000 species of plant and 8 million species of insect, that works out at one plant species for every 27 insect species. Crude though this calculation is, it is indicative. Of course, the relationships between plants and insects are greatly varied: a few insect species rely on a single plant species, whereas many link up with dozens of plants.

Will these Membracis treehoppers join countless other insect species on the road to extinction? Credit: M. FOGDEN/PHOTOLIBRARY

Some observers may respond that if thousands of insect species are becoming extinct, so what? Do we really need all those creepy-crawlies? This point applies particularly to beetles, which must total several million species, many of them only marginally differentiated in their morphologies. Yet this apparent redundancy may serve some vital function in nature, if only as an evolutionary insurance mechanism. Still more to the point is that insects supply a host of ecosystem services that support the human enterprise. If we were eventually to lose half of all mammal and bird species, as looks entirely possible, that would surely be less damaging than losing half of all insect species with their pollinating services: our agricultural crops could be in trouble within short order. We live in a bug-driven world.

All this is dealt with in splendid detail in this book by Michael Samways, a leading entomologist at Stellenbosch University in South Africa. He starts out with the rationales for insect conservation, then considers such esoteric factors as evolutionary radiation, flight mechanisms, polymorphisms and taxonomic challenges. He reviews insects' roles as keystone organisms, soil modifiers, pollinators, parasitoids and predators, and disease vectors. He considers insect survival in a fast-changing world, assessing such issues as environmental contamination, agricultural encroachment, deforestation, threats from invasive aliens, biological controls, genetic engineering, climate change and future evolution, as well as synergized interactions between these factors. The book concludes with an extended evaluation of conservation strategies, including reserve selection, plant and animal surrogates, phylogenetic considerations, inventorying and monitoring, species restoration, triage conservation (focusing efforts on the top priorities), and biodiversity hotspots as applied to insects.

Samways displays a flair for engaging asides, such as his comment on insects' fecundity: “One gravid aphid, left to reproduce with zero mortality, will, after one year, cover the globe with an aphid layer over 140 km thick.”

There are very few insect books of such expansive scope, and this one could be a standard text for years. It will be welcomed by specialists in entomology, biodiversity, mass extinction, evolution and half-a-dozen associated fields. But it is much more than an expert book for experts; it should appeal to everyone interested in the fast-diminishing biodiversity of our planet. All in all, this is an expensive book that is excellent value.