Colony founding by slave-maker queens is also typically aggressive,
with newly mated queens often appearing to use the same lethal weapons
and fighting tactics during their solitary assaults on host-species nests
as do their workers during slave raids. However, in some cases, less
aggressive tactics come into play, and chemical propaganda or appease-
ment substances are sometimes used (Stuart, 1984; Buschinger, 1986,
1989; Topoff, 1997).
Queens of variousFormicaspecies in Europe that are facultative
temporary social parasites illustrate a range of tactics for dealing with
colony defences (see Hölldobler and Wilson, 1990, and references
therein). Young queens ofFormica rufaplunge directly into host nests
and, although many are killed, enough survive to make this ant extremely
common and widespread. Queens ofFormica exsectaexhibit a more
cautious approach and initially ‘stalk’ host nests and then either enter by
stealth or are carried in by host workers, which display relatively little
hostility to the parasite. Queens ofFormica pressilabrisreportedly lie
down and ‘play dead’, assuming a pupal position, and are then picked up
by host workers and carried into the nest without any apparent hostility.
For certain Lasius species, temporary parasitism is apparently
obligatory (see Hölldobler and Wilson, 1990, and references therein).
Colony-foundingLasius umbratis queens first attack and kill a host
worker and carry it around for a time, before attempting to enter the host
nest. Queens ofLasius reginaeeliminate host queens by rolling them over
and ‘throttling’ them, biting the ventral neck region until they are dead.
Queens of the temporary social parasitesBothriomyrmex decapitansand
Bothyriomyrmex regicidusexhibit similar behaviours (see Hölldobler and
Wilson, 1990, and references therein). The parasites are initially attacked
and dragged into the host nest by host workers but ultimately find their
way on to the back of the host queen, where they slowly and meticulously
cut off her head. Often the parasite queens appear extremely attractive to
host workers, probably because of chemical attractants or appeasement
substances, and in some cases it is the host workers that kill their own
queens, once the parasite has become accepted into the colony. Thus,
social parasites appear to use a variety of behavioural and chemical means
to penetrate host nests, eliminate host queens and secure adoption by host
workers.Evolution
The evolution of social parasitism in social insects has been a topic of
speculation and debate since the time of Darwin, and numerous factors
are likely to have contributed to the evolution of this phenomenon and its
various manifestations in different phylogenetic lines. Hölldobler and
Wilson (1990) summarized the possible evolutionary relationships among
free-living and socially parasitic species (see Fig. 15.1) and most of the
links indicated are well supported by comparative data. However, some328 R.J. Stuart