In this study we report a case of ant-trail following by lycaenid cate
rpillars. Euliphyra mirifica and E. leucyana caterpillars are involved
in a commensal association with the weaver ant Oecophylla longinoda.
The host nests are made with leaves which over the course of time dry
out or are broken open by storms, forcing the ants to migrate and buil
d a new nest elsewhere. Euliphyra caterpillars are stimulated by recru
itment behaviour which triggers the migration of their host. They then
follow the host trails leading to the new nesting site. Laboratory ex
periments showed that these caterpillars are able to follow host trail
s under varied conditions: (1) fresh trails actually used by workers,
(2) fresh trails in the absence of workers, (3) heterocolonial, 2-mont
h-old trails, and (4) fresh trails washed with water (to simulate the
effect of tropical rains). They can also bridge trail gaps of more tha
n 1 cm. Under natural conditions, the trails are frequently situated a
long thin twigs. The forward progress of the ants in such a situation
is not impeded by the presence of large Euliphyra larvae. Workers just
climb over the caterpillars, even on larger trails where there is eno
ugh room to pass alongside them. This suggests that an allomone is sec
reted on the dorsal part of the caterpillars. When crawling along hete
rocolonial trails, the caterpillars are not attacked, even if about 21
% of the workers from the new colony spread their mandibles when encou
ntering them. They are then adopted and are admitted to the nest of th
e new host colony of O. longinoda.