  We study the ground state and excitation spectrum of a quasi one-dimensional
nanostructure consisting of a pole and rungs oriented in the opposite
directions ("centipede ladder", CL) at quarter filling. The spin and charge
excitation spectra are found in the limits of small and large longitudinal
hopping $t_\|$ compared to the on-rung hopping rate $t_\perp$ and exchange
coupling $I_\perp$. At small $t_\|$ the system with ferromagnetic on-rung
exchange demonstrates instability against dimerization. Coherent propagation of
charge transfer excitons is possible in this limit. At large $t_\|$ CL behaves
like two-orbital Hubbard chain, but the gap opens in the charge excitation
spectrum thus reducing the symmetry from SU(4) to SU(2). The spin excitations
are always gapless and their dispersion changes from quadratic magnon-like for
ferromagnetic on-rung exchange to linear spinon-like for antiferromagnetic
on-rung exchange in weak longitudinal hopping limit.
