We used a fluorescence technique to mark and re-count the invasive earthworm, Pontoscolex corethrurus from PVC tubes established in a forest and a recently abandoned pasture in Puerto Rico to test the effects of the labeling treatment on earthworm population survival over time. A fluorescent marker was injected into the earthworms in the middle third section of the body, between inside and outside walls. Five labeled juveniles and two unlabeled adults of P. corethrurus were incubated in the PVC tubes under field conditions and retrieved after 2, 4, 8, and 16 weeks (labeled population; four PVC tubes harvested per date and site for a total of 32 tubes). Concurrently, an additional set of 8 PVC tubes contained five unlabeled juveniles and two unlabeled adults each of P. corethrurus (unlabeled population) was established in each site (forest and pasture; 16 tubes total) to compare the percent remaining of worms in tubes containing labeled and unlabeled populations after 2 and 16 weeks (4 replicates per date). We found that (1) the fluorescent marker was still present in the earthworm tissue after four months, (2) the percent remaining of the total earthworm population was not significantly different between the forest and pasture sites, and (3) thirty percent of the labeled worms were lost after 2 weeks, but the population remained stable between week two and four of the experiment. Our results suggest that fluorescent markers can be a useful tool for carrying out short term mark and re-count studies of earthworms.