74 
Psyche 
[June 
In the course of a few minutes while Mrs. Brues secured 
some motion pictures of their movements, the swarm had 
advanced several feet over the irregular terrain. We col- 
lected about one-third of the marching larvae and a sub- 
sequent count of these indicates that some 900-1200 larvae 
were taking part in the procession. This total is surpris- 
ingly small and far less than a rough estimate made at the 
time the swarm was observed. 
No stragglers were seen in the neighborhood of the crawl- 
ing swarm in spite of the very irregular surface over which 
it traveled. The band of larvae was by no means of uniform 
breadth or thickness, swelling and contracting constantly 
as movement was speeded or slowed by sudden ups and 
downs along the path. Even at points where there were 
very few larvae, those coming up from behind selected with- 
out hesitation the slime trail left by those in advance. 
As all individuals were fully grown and of uniform size 
it appears that migration was not undertaken in search of 
food, but to find suitable conditions for pupation and trans- 
formation. We were unable to find any fleshy fungi from 
which the swarm might have come. In spite of the exces- 
sive moisture in the rain forest, large fungi are compara- 
tively scarce, although diffuse mycelial growths are plentiful 
on the logs, bark and smaller vegetable debris that litter the 
forest floor. In general the insect fauna of this area is not 
rich in mycetophagous forms and very few fungus-gnats 
were present in sweepings made in the vicinity. In common 
with other Mycetophilidae (in the wider sense) the species 
of Sciara are mycetophagous, developing most generally in 
decaying mushrooms and in vegetable material such as tu- 
bers, large seeds, etc., that are disintegrating through the 
action of putrefactive bacteria and fungi. Like some of 
their relatives, the adult midges frequently appear in in- 
credible numbers where such food is available under the 
moist conditions essential to their larval development. 
As would be expected the earlier observations were re- 
corded by European entomologists. These have been re- 
ferred to in several American publications. Johannsen ('09) 
states that the European Heerwurm is probably Sciara, 
thomae L. or S. militaris , probably the latter. 
