Worcestershire Record No. 16 April 2004 pp. 29-30

Geoff Trevis

This revision concerns the two species, L. niger and L.alienus, referred to in my separate summary of the aculeate hymenoptera of Worcestershire. In 1992 Seifert published details of the revision splitting L. niger into L. niger (sensuo stricto – s.s.) and L. platythorax, and L. alienus into L. alienus (s.s.) and L. psammophilus. All previous records can now only be given the status sensuo lato (s.l.). Glenda Orledge is co-ordinating a national survey of these species on behalf of the Bees, Wasps and Ants Recording Society (BWARS) and I am grateful to her for the information summarised in this article.

Each of the pairs is difficult to separate morphologically and valuable keys are provided by Blacker and Collingwood (2002) and Czechowski et al. (2002). A useful starting point for identification is the habitat from which ants are collected. L. niger prefers relatively dry situations in grassland or under stones and slabs in gardens whilst L. platythorax will be found in wet, boggy places, nesting in rotting trees stumps. L. alienus appears to favour dry, sparse grassland where there will be minimal competition from L. flavus and Myrmica species and L. psammophilus will be located in acid heathland. L. alienus records from Devil’s Spittleful may well be L. psammophilus. However, the habitat preferences do overlap and are not definitive.

The following features published by Orledge (2003) were found helpful when practical work was undertaken at a BWARS workshop and are quoted in full:

Lasius niger and Lasius platythorax

· Clypeal pubescence: relatively dense in L. niger, relatively sparse in L. platythorax. Seifert quantifies this character and gives it prominence. It is well described by and figured by Chezchowski et al., who also give it prominence. It appears to be a reliable character, but requires careful positioning of the specimen with respect to light source for correct observation.

· Clypeal convexity: in lateral profile, and ignoring the extent of development of the clypeal carina, the clypeus of L. niger is more convex than that of L. platythorax. It appears, also, that whilst clypeal convexity in L. platythorax is fairly even, in L. niger the upper part of the clypeus can be more strongly convex than the lower part. Whether this is always the case needs further checking.

· Dorsal pronotal hairs: relatively short and of more or less even length in L. niger; longer, and of unequal length in L. platythorax. Seifert quantifies worker pronotal hair length by dividing the length of the longest standing hair on the pronotum by head length (maximum length along median line). He gives a value for this ratio of 0.119 ± 0.009 for L. niger and of 0.159 ± 0.010 for L. platythorax.

Lasius alienus and Lasius psammophilus

For separating the workers of these species the only character which appears satisfactory is the number of short hairs on the sloping face of the propodeum, between the propodeal spiracle and the metapleural gland. On each side L. alienus has 0 – 1, rarely 2, hairs, whilst L. psammophilus has 2 – 5 hairs. Some specimens may remain problematic. The presence of suberect hairs on the hind tibia is mentioned by Seifert and used by Blacker & Collingwood, but this character proved to be unsatisfactory for the specimens examined at the BWARS workshop. Whether or not the number and extent of occipital setae (well described and figured by Czechowski et al.) is a useful separator for British material remains to be seen.

Guidance notes on collecting and recording the species

1. When a nest is located, it is important to take a sample of several workers. When possible, males and alate females should also be collected. Where only individual foragers are seen, try to collect several.

2. Since body hairs are of paramount importance for the separation of the species, specimens need to be either mounted or preserved in alcohol as soon as possible after capture. Unfortunately, since hairs abrade easily, dry, unmounted specimens are of little use.

3. For each collection, note both the grid reference (ideally 6 figure) and date.

4. For each collection, note the habitat (heath, marshy ground, urban pavement etc.), and the location within that habitat (rotten log, dry soil, under stone etc.).