Increased transmission of parasites and diseases is generally consider
ed as a major cost of social life. In this study we tested the hypothe
sis regarding ectoparasites as a cost of living in crowded habitats in
the common lizard (Lacerta vivipara). We used two approaches to explo
re this question. First, we tested if ectoparasite load and prevalence
are positively correlated with host density in the field. Second, we
experimentally tested if lizards avoid parasitized conspecifics. Contr
ary to expectation, we found that (1) ectoparasite load is negatively
correlated with lizard density; (2) prevalence does not significantly
increase with density; (3) unparasitized lizards do not avoid parasiti
zed conspecifics but are attracted by them whatever their parasite loa
d. These findings suggest that ectoparasites cannot be considered as a
cost of living at high density in the common lizard, in spite of the
potential negative impact mites may have on lizard fitness.