Compared with the majority of the country the millipede fauna of Suffolk is relatively well known. However, no members of the family Chordeumatidae have been recorded from the county. Five species occupying two genera are currently known in Britain. The three British Melogona millipedes are small species, 5-10mm in length and less than 1mm in diameter. They are white to cream in colour and on closer examination display prominent ‘cheeks’ typical of the family. Above each cheek is a narrow, elongate triangular eye composed of five, six or seven vertical rows of up to four tiny black dots. The two British Chordeuma species are larger (length 10-13mm, diameter 1.2-1.5mm) and brownish in colour. They still have the prominent ‘cheeks’ but each eye forms an equilateral triangle. Although the national atlas (Lee, P. 2006. Atlas of the Millipedes (Diplopoda) of Britain and Ireland.Pensoft.) shows that all of the chordeumatids have a western bias to their distribution, the most widespread of these millipedes, Melogona scutellaris, does occur in Essex. Based on current distribution patterns, two other species, Chordeuma proximum and Melogona gallica, could conceivably occur in Suffolk also.

Chordeumatid millipedes typically have an annual life cycle. They usually occur in leaf litter in woodland habitats and are adult and active in the winter months. Collecting invertebrates in the midst of winter can be uncomfortable and this means that they are often under recorded even within the core of their range. One option the less hardy naturalist can consider is to remove the habitat to a more comfortable location; the leaf litter can be collected and then sorted through in warmer conditions, possibly on the dining room table if you can get away with it! However, it is often considered more efficient to use an extraction technique to separate small, relatively inactive invertebrates from the substrate.

Most SNS members have probably come across the Tullgren funnel in their school studies if nowhere else. Basically this consists of a funnel with a small sieve or circular piece of mesh placed in the top. The litter sample is put in the sieve / mesh and a heat source e.g. a light bulb is arranged above it. The heat dries out the litter from above forcing invertebrates to move down through the litter to find the moist conditions they prefer. Eventually they reach the bottom and end up falling through the holes of the sieve and down the funnel into a collecting pot. For the amateur, Tullgren funnel extraction is really only feasible with small volumes of material yet the process is least efficient in such circumstances as the litter is more likely to dry out too rapidly. A more practical alternative is to allow a larger volume of litter to dry naturally in a Winkler extractor. Although similar in principle to Tullgen funnel extraction, in a Winkler extractor the funnel (and sometimes the sieve) is replaced by a net. There are conflicting reports on the efficiency of these extraction methods compared with each other and other extraction techniques. However, there can be no argument that using an extraction technique is a more naturalist friendly way of recording litter invertebrates than crawling around on hands and knees in cold, damp conditions in the depths of winter.

As with most specialist equipment, Winkler nets can be expensive to buy. Therefore, with support from an SNS bursary, I set about producing a simple homemade version to enable leaf litter from Suffolk woodlands to be checked for the presence of chordeumatid millipedes. The extraction ‘funnels’ were constructed from rectangular plastic compost sieves (approx. 45x30cm) hung from the rafters of an unheated garage. Heavy gauge polythene sacks were taped below the sieves and the lowest corner of each sack was cut away. A large collecting pot containing 50% alcohol was taped into each of the resulting openings.

Once the extraction units were prepared, three woodland sites in the south of Suffolk (hence closest to the known Essex locations for Melogona scutellaris) were selected. Table 1 gives details of these sites. The woodlands were visited on 30th January 2007 and five samples of approximately one litre of leaf litter were collected from each. The litter was transported in sealed plastic bags and once at home was transferred to the Winkler funnels for the extraction of millipedes and other invertebrates. The litter remained in the sieves until the end of April 2007 but animals falling into the collecting pots were removed approximately every fortnight. Where feasible all invertebrate specimens were identified to species.

Table 1. Details of site visited for collection of leaf litter

Table 2 lists the invertebrates identified from the litter samples. As can be seen from the Table only three species of millipede were collected and none of these was the chordeumatids that were being sought. Previous work in all three woodlands has produced good lists of millipedes collected by hand searching. Clearly the majority of these millipede species were not detected by Winkler extraction and all of the species that were extracted had already been recorded by hand collecting. The low diversity of species extracted was notable in the other invertebrate groups also. This may have been due to the litter samples being collected just once, early in the year. At the end of January some invertebrates probably were to be found deeper in the soil rather than in surface layers of litter where conditions are colder and drier. It has often been noted that after a hard frost small, soil-dwelling millipedes such as chordeumatids are readily collected from under stones on the soil surface but these tend to be adult or sub-adult animals. The immature stages are seen much less frequently and could well have overwintered deeper in the substrate. On reflection it would have been sensible to try and extract millipedes from the soil as well as the leaf litter and to collect new samples each month through to April in order to monitor any emergence of maturing millipedes at the surface.

One positive outcome of this work was that relatively large samples of the very common pygmy woodlouse Trichoniscus pusillus were collected. Taxonomists have recently split the species and recognition of the two requires dissection of the males. To make this more difficult one of the species, Trichoniscus pusillus s.s., is parthenogenetic and hence any population is composed mainly of females. Only a very few males are produced and these contribute little to the genetics of the population. In the other species, Trichoniscus provisorius, males and females are produced in roughly equal numbers. This means that often it is not possible to be certain as to which species is present on a site if only small numbers of females are collected. All of the specimens extracted from litter from Bentley Old Hall Wood were female and so probably were Trichoniscus pusillus s.s. but it was necessary to record them as Trichoniscus pusillus agg. because without a male specimen to dissect it was not possible to be certain of the identification. There were males amongst the sample from Ramsey Wood and the presence of a population of Trichoniscus provisorius here was confirmed. However, there were many more female than male specimens in the sample indicating that a population of Trichoniscus pusillus s.s. was probably also present but again without a male these were recorded as Trichoniscus pusillus agg.

The small number of samples worked on in 2007 was not sufficient to provide a definitive answer to the question posed in the title of this piece. The exercise did provide some indications as to how the sampling might be improved to increase the probability of detecting the annual millipede fauna of woodland litter.

Fig. 1 Tullgren funnel (from Green, Stout & Taylor, Biological Science Vols I & II, 2nd Ed.
By kind permission of Cambridge University Press)

Table 2. Taxa extracted from leaf litter samples

Acknowledgements

A SNS bursary was kindly granted to support this work. Mark Nowers of the RSPB granted permission to work in the Hintlesham Woods and Mr John & Mrs Annie Owen granted permission to work in Bentley Old Hall Wood. Roger Booth of the NHM assisted with identification of the Aleocharine beetles.