BEHAVIOR
Centipedes are primarily adapted for speed. Any
long, slender object that moves forward rapidly generates
lateral undulations that counter the forward movement
(like the side-to-side swaying of a train), so centipedes
have developed anatomical modifications to dampen or reduce
the undulations. These include tergite "heteronomy"
(well developed in Lithobiomorpha, poorly developed in
Scolopendromorpha), which shortens the body while maintaining
the same number of legs to propel it forward, and tergal
fusion (in Scutigermorpha), which strengthens the body
and makes it more rigid at the positions where undulations
develop. The Geophilomorpha are the exception, as they
are slow-moving and adapted for burrowing by elongating
and contracting the body.
Millipedes
are slow-moving and adapted for burrowing, for which three
mechanisms are known. The burrowing power is generated
by the legs, and at any moment in time, most of a millipede's
legs are on the ground pushing backwards, thereby propelling
the animal forward. Some millipedes have lost the ability
to burrow and now are either surface active and relatively
fleet (through much slower than centipedes) or inhabit
cracks and crevices formed by other organisms.
1)
Bulldozing: the millipede lowers its head and rams
straight ahead. This behavior is shown by the cylindrical
millipedes, whose bodies are of equal widths throughout,
so the head prepares a path that the rest of the body
can follow.
2)
Wedging: the head/anterior end is inserted into
a crevice and the legs, by pushing upwards and straightening,
cause the crevice to widen, allowing further penetration
by the anterior end. This behavior is shown by the "flat-back"
millipedes, in which the paranota constitute the pushing
surface and tend to split matter in a horizontal plan,
like matted layers of leaves.
3)
Boring: segments of progressively greater width
are dragged forward, widening a crevice. In millipedes
showing this behavior, the anterior end is narrow and
each segment is slightly wider than the preceding one.
