The larva of the bagworm moth Eumeta crameri Westwood
uses sticks (either thorns/twigs or both) as materials
for building its protective case. During the course
of its growth and development, the larva renovates its
case three times and at each instance it increases the
volume of its case by replacing older sticks by newer
and longer ones. In the present study we have measured
the length of the longest sticks in addition to
larval length and head capsule width soon after the
completion of each instance of case renovation to compute
Dyar’s coefficient. Interestingly, we have observed
that increase in the size of the longest stick during
successive instances of case renovation follows Dyar’s
law very closely. Dyar’s coefficient showed spectacular
constancy when computed by using the data on
the length of the longest sticks. What is most surprising
is that a stick is an inanimate object, yet the
pattern of its increment during the life cycle of the
bagworm moth confirms Dyar’s principle much in the
same way as other biological variables, such as larval
length and head capsule width, do. This study uses an
inanimate object to compute Dyar’s coefficient.