ARMY ANTS IN BRITISH GUIANA. 295 



of small flies of the Conopid genus Stylogaster and of the family 

 Tachinidfe, which hover over the van, and third, the plundering of 

 the larvpe and pup.T from the nests of the most diverse ants. The 

 army that attempted to enter the kitchen had plundered all the nests 

 of PJieidoJe fallax and of an allied species in the sandy yard of the 

 laboratory and had temporarily stored the larvae, pupae and young 

 callows in piles like handfuls of rice around the bases of the tall 

 Javanese bamboo clumps. This army also attacked a flourishing 

 colony of yellow wasps {Polybia sp.) in the wall of the kitchen, ex- 

 pelled the workers and carried off the brood. 



The swarms of small flies above mentioned were regularly seen 

 hovering from one to two feet abo^"e the advancing columns of ants. 

 Bates (1863), who seems to have been the first to observe this singular 

 phenomenon, says: "The armies of all Ecitons are accompanied by 

 small swarms of a kind of two-winged fly, the females of which have 

 a very long ovipositor, and which belongs to the genus Stylogaster 

 (family Conopsidse). These swarms hover with rapidly vibrating 

 wings, at a height of a foot or less from the soil, and occasionally one 

 of the flies darts with great quickness towards the ground. I found 

 they were not occupied in transfixing ants, although they have a long 

 needle-shaped proboscis, which suggests that conclusion, but most 

 probably in depositing their eggs in the soft bodies of insects, which 

 the ants were dri\dng away from their hiding-places. These eggs 

 would hatch after the ants had placed their booty in their hive as 

 food for their young. If this supposition be correct, the Stylogaster 

 would offer a case of parasitism of quite a novel kind." Townsend 

 also gives an account of Stylogaster, which he observed in 1897 in the 

 State of Vera Cruz: "Fifty-one specimens of this interesting genus 

 were taken hovering over the front ranks of a mo\'ing army of ants, 

 in a cafetal at Paso de Telayo, during the last hour or two of daylight 

 on March 29. In company with them were numerous specimens of 

 Hyalomyia and some other small tachinids. The ants have been 

 determined by Mr. Theo. Pergande as Ecitonforeli Mayr [= burchelU 

 Westw.]. . .The column of ants was about 15 feet wide and 25 feet 

 long, and moved slowl;^' but surely through the cafetal, swarming 

 rapidly over the thick covering of dead leaves, branches and other 

 obstructions that strewed the ground under the coffee-trees. The 

 specimens of Stylogaster hovered continually over the ants, now and 

 again darting at them, without doubt for the purpose of ovipositing 

 in their bodies. During the whole three months of my collecting in 

 this locality, I saw not a single specimen of Stylogaster at any other 



