Myrmica hirsuta

In Central Europe M. hirsuta is clearly and obligatory social parasite of Myrmica sabuleti. It produces workers only very rarely: three entire host colonies of M. sabuleti from Denmark were collected and examined yielding only 3 M. hirsuta workers. It is probable that if host colonies for other related social parasites, such as Myrmica laurae, were exhaustively searched in the same way, a few workers of these species might be located. Its nearest relative, Myrmica bibikoffi, has been recorded as free living. So, these species might illustrate trend from temporary social parasitism and facultative social parasitism (with some workers) in certain ecological conditions, to obligatory social parasitism with just a few workers being produced in some conditions. In northern Europe, M. hirsuta has been found living in Myrmica lonae colonies. This could indicate a degree of host transference but equally might indicate that M. lonae is only an "ecological race" of M. sabuleti. In our experience M. hirsuta occurs wherever a strong population of M. sabuleti exists, but on average only about 1 in 50-100 host colonies are infested (Elmes 1983). Thus one has to examine a large number of host colonies before finding M. hirsuta; generally this is easier when the host lives under stones. (Radchenko and Elmes 2003)

Identification
A member of the sabuleti complex of the scabrinodis species group (Radchenko and Elmes 2004). Similar to a microgyne Myrmica sabuleti but distinguished by the laterally enlarged post petiole, wider frons and excessive development of body hairs. Head width: 1.05 mm. Body length: 5.2 mm. Mean postpetiole width: 0.675 mm. (Collingwood 1979). M. hirsuta is generally most similar to Myrmica bibikoffi while the queens are superficially similar to Myrmica laurae. (Radchenko and Elmes 2003)

Distribution
Very widely distributed throughout Western Europe and also found in southern England.

Distribution based on Regional Taxon Lists
Palaearctic Region: Austria, Belgium, Croatia, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Netherlands, Poland, Russian Federation, Serbia, Slovakia, Sweden, United Kingdom of Great Britain and Northern Ireland.

Biology
When Elmes (1978) described M. hirsute from southern England, he considered it to be a workerless social parasite of Myrmica sabuleti. Later, in infested nests from Denmark he found two workers (Elmes 1994), both are pseudogyne, having minute ocelli and at least a trace of scutum.

Radchenko and Elmes (2010) - In Central Europe M. hirsuta is clearly an obligatory social parasite of M. sabuleti. In North Europe, M. hirsuta usually lives in Myrmica lonae colonies. This could indicate a degree of host transference but equally might indicate that M. lonae is only an “ecological race” of M. sabuleti (see Notes to M. lonae).

The worker caste is produced only very rarely: three entire infested host colonies of M. sabuleti from Denmark were collected and each worker examined, this yielding only 3 M. hirsuta workers (2 from one colony and 1 from another). Although 8 entire infested colonies were collected at the type locality (Elmes 1978) only queens and males were examined individually, so it was possible these colonies also contained a few very worker-like pseudogynes. We suggest that if host colonies infested by other related social parasites, such as M. laurae, were exhaustively searched in the same way, a few workers of these species might be found. Elmes (1983) showed that in the laboratory M. hirsuta queens produced two types of offspring: larger larvae develop slowly, overwinter and eclose to become new fully reproductive M. hirsuta gynes the following spring, whereas smaller larvae either develop quickly and eclose the same summer, becoming infertile (no spermatheca) intercastes (winged workers), or they overwinter and eclose to become infertile (or sub-fertile) small M. hirsuta queens. M. hirsuta queens can suppress the sexual development of their host's larvae, but their own larvae appear to be “immune” to queen effect (Elmes 1983).

Pitfall trapping showed M. hirsuta queens were present in traps from August to October, numbers peaking in early September, at four sites in Southern England where the host is common (Elmes 1982). Other similar studies (unpublished) confirm this trend so that one might state with reasonable confidence that on sites where M. sabuleti is the dominant species of Myrmica, one might expect to find some colonies infested with M. hirsuta. Even so, the levels of infestation is not high on average only about 1 in 50-100 host colonies are infested (Elmes 1983), thus one has to examine a large number of host colonies before finding M. hirsuta; generally this is easier when the host lives under stones. However, infested colonies tend to be clumped as was the case at the type locality and in Denmark, while Seifert (1988) found that up to 50% of colonies were infested on one small site. The low density of overall infestation combined with the apparent availability of young queens searching for host colonies in autumn, suggests that penetration of new host colonies might be quite difficult. Elmes (1983) had results that suggested that once insinuated into a host nest, a M. hirsuta queen might delay or suppress the onset of oviposition of the host queen by several weeks. If this is correct then it might be a way in which the relatively low number of eggs laid by the parasite might avoid direct competition with the much larger number of eggs laid by the host.

It was suggested (Elmes 1978b) that there might be a trend for extreme polygyny to “degenerate” into social parasitism via forms such as microgyne M. rubra. Certainly, the closest relative of M. hirsuta genetically is M. sabuleti (Savolainen and Vepsalainen 2003). On the other hand, its closest relative among the social parasites, M. bibikoffi (see above), has been recorded as free living and in mixed colonies with M. sabuleti and arguably this could illustrate a trend from temporary social parasitism to facultative social parasitism (with some workers) in certain ecological conditions, to obligate social parasitism with just a few workers being produced in some conditions.

Castes
Queens and males are commonly present. Workers are relatively rare in this social parasite.

Nomenclature

 *  hirsuta. Myrmica hirsuta Elmes, 1978: 131, fig. 2 (q.m.) GREAT BRITAIN. Elmes, 1994: 439 (w.). See also: Collingwood, 1979: 51; Bolton, 1988a: 4; Radchenko & Elmes, 2003a: 228; Radchenko & Elmes, 2010: 149.

Worker
Radchenko and Elmes (2003) - (n=3): HL 1.02-1.06; HW 0.88-0.95; SL 0.78-0.80; AL 1.46-1.56 mm; FI 0.40-0.42; FLT 1.17-1.23; SI1 0.75-0.78; SI2 0.84-0.91; PPI 0.55-0.58; ESLI 0.34-0.37; queens (n=36, paratypes): HL 1.00-1.18; HW 0.88-1.10; SL 0.72-0.88; AL 1.62-2.00 mm; FI 0.39-0.46; FLI 1.10-1.30; SI1 0.68-0.81; SI2 0.73-0.84; PPI 0.57-0.72; ESLI 0.24-0.36; males (n=21, paratypes): HL 0.82-0.94; HW 0.80-0.88; SL 0.43-0.50; AL 1.66-1.92 mm; SI1 0.50-0.58; SI2 0.52-0.63; PPI 0.63-0.73; ESLI 0.06-0.12.

Type Material
Radchenko and Elmes (2010) - Holotype, q, “Durlstone Country Park, Purbeck, Dorset ., 1973, Leg. GW Elmes” (LONDON); paratypes: 34 q, 19 m, Durleston Country Park, Purbeck, Dorset, UK, under stone, limestone grassland, leg. G. W. Elmes, 1973 (in 9 different infested colonies of M. sabuleti) (LONDON, ELMES, KIEV)