A century of invasion – an unwelcome newcomer in northern waters

The Manchester Museum’s specimen of the male Chinese Mitten Crab (Eriocheir sinensis), collected from Ribble Estuary, Lancashire, in 2007.

The Chinese Mitten Crab (Eriocheir sinensis) is an accidentally imported species in the North Sea, which is considered one of the World’s 100 worst invasive species. The crab first appeared in northern Germany in 1912. It was unintentionally brought from China, apparently as a stowaway in the ballast tanks of cargo ships. Since 1912, the crab has dramatically spread over northern Europe. It was first recorded from Thames River in 1935. Now it is also established in the Rivers Humber, Medway, Tyne, Wharfe and Ouse, increasing its range throughout England and Wales by several tens of kilometres a year. See here about Mitten Crab recording project in the UK.

This crab lives both in fresh and salt waters. In autumn, adult crabs undertake a mass migration from freshwaters to river estuaries for reproduction, crossing long distances over dry land. In October-December, crabs mate, females produce eggs and move deeper to the sea where eggs and several larval stages develop. Young crabs migrate back to freshwaters. They reach sexual maturity in three years and then migrate back to the sea to reproduce.

These crabs can cause serious ecological damage. As adults usually burrow in muddy riverbanks, they can damage them, modify natural habitats and compete with native species. There are no effective means to control this crab species. In Germany, special traps were used during mass crab migrations, but they proved to be ineffective. However, the crabs are edible and even considered delicacy in China. Thus, maybe these crabs should just ‘be eaten’ to stop them damaging British wildlife (see more about this)?

In the vide below, Dr Malcolm Greenhalgh, the author of the notable book on the British Freshwater Life is talking about the Chinese Mitten Crab and the first male specimen collected from North-West.

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Imported with bananas – what are you, a Banana Spider?

In late January 2017, Ms Eleanor Smith of Wilmslow (Cheshire, UK) visited the Manchester Museum and brought a medium-sized spider (see Fig. 1) that was found alive in a bunch of bananas, in a supermarket (Lidl) near Wilmslow. As she was told, the bananas on which the spider was found were delivered from Colombia. Unfortunately, the spider was already dead because Eleanor had kept the jar with the spider in a fridge; far too cold for such a tropical creature. The specimen was found to belong to what is commonly known as ‘Banana Spiders’. It was a mature female that was identified as Sadala sp. in the family Sparassidae, huntsman spiders. The specimen is now deposited in the Manchester Museum’s spider collection (accession number G7585.1).

Fig.1Female of Sadala sp. (Sparassidae) imported to the UK from Colombia; the Manchester Museum (G7585.1).

Spiders that are incidentally imported with bananas are commonly called ‘Banana Spiders’. However, this common English name is rather misleading, as it is used for quite a number of different spider groups.

In North America, this name can be applied to Golden Orb-web Spiders (Nephila species, family Nephilidae – most commonly Nephila clavipes); see also here and here. The reasons why this species is called ‘Banana Spider’ remain unclear, for there is no obvious connection between the spider and bananas – could it be because of the banana-shaped abdomen of rather large females? By the way, some Nephila species are edible and even considered a delicacy by indigenous people in New Caledonia and Australia, for instance, Nephila edulis (and here).

The wandering spiders (family Ctenidae) are regularly called ‘Banana Spiders’ as well (see Vetter et al., 2014). Some of them have even acquired a very bad media-reputation as deadly venomous species: for instance, the Brazilian Wandering Spider (Phoneutria fera). Alas, most of online media reports – for instance, ‘MailOne’ (24 June 2015) or ‘Independent’ (21 September 2016) – cannot be taken seriously, as they fail to even provide a correct identification of the spiders found on bananas.

In reality, to date, there has been only one published record of the Brazilian Wandering Spider as being imported to Europe (Germany) in 1950s, but yet the identification of that specimen causes doubts. The majority of existing records of “Brazilian Wandering Spiders”, both from Europe and from North America, are likely to belong either to the harmless Central American spider genus, Cupiennius (Ctenidae), or (much rarer!) to other Phoneutria species – most commonly, to Phoneutria boliviensis, a medically important wandering spider from Central America.

By far the most common spider group being imported with bananas is the pantropical huntsman spiders (family Sparassidae), also called ‘Banana Spiders’. In total, 13 species of huntsman spiders have been identified of those imported with bananas and other international goods to Europe. At least five species of huntsman spiders have been reported as being imported with bananas to the UK (Browning, 1954; Wilson, 2011): Barylestis occidentalis, Barylestis scutatus, Barylestis variatus (all from Africa), Heteropoda venatoria (from SE Asia, but now pantropical) and Olios sanctivincenti (from Asia). The commonest of them is Heteropoda venatoria, which is even established indoor in some regions of southern Europe (see Fig. 2). Yet, a real number of imported huntsman spiders might be much higher; Sadala sp. which was mentioned above (Fig. 1) is a new record from this group.

Fig.2. Female (top) and male (bottom) of Heteropoda venatoria (Sparassidae);the Manchester Museum.

The spider collection of the Manchester Museum contains a number of samples of huntsman spiders collected from bananas in Manchester and its vicinities; for instance, from the Manchester Market Street in June 1912 or April 1931 (Fig. 3).

Several spider species that were obtained from the Manchester Open Air Market from imported bananas; the Manchester Museum.

Overall, a number of alien spider species that are imported with bananas and other international cargo to Europe or North America is rather high. For instance, Nentwig (2015) listed 184 species that have been imported to Europe over the last 200 years; of them 47 species have established there in and around human buildings. Vetter et al. (2014) identified 135 spider species imported to the USA in seven years (between 2006 and 2010). Although in the past banana or other fruit shipments were the main pathway of introduction to Europe, today potted plants and apparently container shipments in general are more important. It is suspected that due to the increasing international trade volume and climate change, in the next decades at least one new spider species will be introduced to Europe and established there annually.

Further reading

Nentwig W. (2015) Introduction, establishment rate, pathways and impact of spiders alien to Europe – Biol Invasions, 17: 2757–2778. DOI 10.1007/s10530-015-0912-5

Nentwig W. and Kobelt M. (2010) Spiders (Araneae). Chapter 7.3 – BioRisk, 4(1): 131–147. doi: 10.3897/biorisk.4.48

Vetter R.S., Crawford R.L., and Buckle D.J. (2014) spiders (Araneae) found in bananas and other international cargo submitted to North American arachnologists for identification – Journal of Medical Entomology, 51(6): 1136–1143. URL: http://www.bioone.org/doi/full/10.1603/ME14037

Wilson R. (2011) Some tropical spiders recorded in Leeds, West Yorkshire and a review of non-native taxa recorded in the UK – The Newsletters of the British Arachnological Society, No.120: 1–5.

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