All the lonely beetles, where do they all come from?

Shortly before World War II, London’s Natural History Museum published the first edition of Common Insect Pests of Stored Food Products (Hinton & Corbet 1943), a slim volume providing a guide to the identification of such insects. Although not specifically covering beetles or non-native species, the topic is such that many of the species covered were indeed beetles, and that are number of these were introduced to Britain. However, it was not until the publication of Volume 1 of Insect Travellers (Aitken 1975) that the beetles recorded from cargoes imported into Britain were surveyed and presented comprehensively, whether or not they were seen as pest species. In Volume II (Aitken 1984), which covered insects other than beetles, the numbers, types and origins of cargoes were updated,  and extended to cover the period 1957 to 1977. The 1970s saw a shift from cargo stowage in ships’ holds towards the use of freight containers; in turn this led to the decline of ‘traditional’ ports with piecemeal unloading which allowed for easier inspection and application of insecticides. Therefore, ship and wharf inspection was virtually superceded by increased vigilance inland by the 1970s e.g. at the end points of cargo distribution such as factories, warehouses, mills and farms.

Fast-forwarding to 2010, a lot has changed. Britain now has a Non-native Species Secretariat (NNSS) with its associated Non-native Species Information Portal (NNSIP) of factsheets currently in development. In 2005, Natural England undertook an ‘Audit of Non-native Species in England’ which tabulated 2721 species and hybrids, of which 98 were beetles. Looking at these, the origins/native ranges can be approximately split as follows:

Europe 43

Australasia 16

North America 10

Asia (as a whole) 5

Eurasia 5

East Asia 3

South America 3

‘Tropics’ 3

Central America 2

Palaearctic 2

Africa 1

Europe & Africa 1

South Atlantic islands 1

Unknown 3

Although there is some doubt about the origins of some of these (e.g. a few listed under ‘Europe’ could turn out to be Eurasian), by far the most prevalent source of non-native beetle species is elsewhere in Europe, even though Asia, and especially China, is often cited anecdotally as such a source. It is true that many non-native plants originated in China, and that increased Chinese exports are likely to increase the transport of species from East Asia. However,  it should also be remembered that some Chinese beetles found in Britain and elsewhere are particularly striking such as the Asian longhorn beetle (Anoplophora glabripennis) and the citrus longhorn beetle (Anoplophora chinensis). These have in turn induced the production of many factsheets and column-inches about their invasiveness and damage to timber (e.g. Haack et al. 2010) and that the Internet allows much faster and broader familiarisation with such species than was the case when introductions were first being catalogued.

Asian longhorn beetle (Anoplophora glabripennis)

While other invertebrates may show a similar pattern (of 34 spiders on the NNSIP register, 20 are from Europe and none are strictly Asian), looking at new and potential invasive species as a whole (i.e. including all animal taxa) shows a different pattern. For example, since their 2005 audit, Natural England’s horizon-scanning (Parrott et al. 2009) highlights 63 species across its red ‘alert’, yellow ‘watch’, ‘black’ and ‘climate’ lists; of these, North America (13), East Asia (12) and Asia (9) are the key areas of origin with only 5 species originating elsewhere in Europe and 7 more widely in Eurasia.

There are many factors here, but some seem to stand out; 

• Beetles move by many means, often helped by humans, but many introductions into Britain are likely to be from Europe as their ranges expand northwards with climate change.
• Many terrestrial invertebrates, especially small species, can spread to new areas unaided – this is seen with ‘ballooning’ spiders.
• Larger species, particularly invertebrates are often spread intentionally such as fish species introduced for angling or ornamental purposes and subsequently escaping or being released.

So, to return to the title question ‘...where do they all come from?’, the answer is that they are from more-or-less everywhere, but often just across the English Channel – for those of us interested in species recording and finding new beasties, they are likely to keep us busy and there will no doubt be further striking exotics hitting the headlines as they appear in fruit shipments and imported houseplants. Meanwhile, the small and less obvious beetles will be making their quiet way from continental Europe...

References

Aitken, A.D. (1975). Insect Travellers. Volume I. Coleoptera. Technical Bulletin 31. Ministry of Agriculture, Fisheries and Food. HMSO, London.

Aitken, A.D. (1984). Insect Travellers, Volume II. MAFF Agricultural Development and Advisory Service Reference Book 437. HMSO, London.

Hinton, H.E. & Corbet, A.S. (1943). Common Insect Pests of Stored Food Products. British Museum (Natural History), London.

Haack, R., Hérard, F., Sun, J., & Turgeon, J. (2010). Managing invasive populations of Asian longhorned beetle and Citrus longhorned beetle: a wWorldwide perspective Annual Review of Entomology, 55 (1), 521-546 DOI: 10.1146/annurev-ento-112408-085427

Parrott, D., Roy, S., Baker, R., Cannon, R., Eyre, D., Hill, M., Wagner, M., Preston, C., Roy, H., Beckmann, B., Copp, G.H., Edmonds, N., Ellis, J., Laing, I., Britton, J.R., Gozlan, R.E. & Mumford, J. (2009). Horizon Scanning For New Invasive Non-native Animal Species in England. Natural England, Sheffield. (Natural England Contract No. SAE03-02-189, Natural England Commissioned Report NECR009).

Thank you to the US Fish & Wildlife Service for putting this image in the public domain. Much appreciated.