Invertebrates have many useful pharmacological activities. The present investigation aims to study some of these activities in the red swamp crawfish Procambrus clarkii against a varying number of pathogens. Results showed that raw chitosan had molluscicidal and larvicidal effects on both Biomphalaria alexandrina snailsandSchistosoma mansoni larvae. Also, the current study confirmed the inhibitory action of chitosan against three gram-positive bacteria (Streptococcus faecalis, Bacillus subtilis, and Staphylococcus aureus) and three gram-negative bacteria (Neisseria gonorrhoeae, Pseudomonas aeuroginosa and Escherichia coli). Additionally, in the current study chitosan revealed antifungal activity against Candida albicans but no effect was detected against Aspergillus flavus. The present results indicated that chitosan can be used as a molluscicidal agent, a rodenticide against the albino rat and insecticide against adults of the tiny black ants, Monomorium minimum. For the first time, under field conditions, raw chitosan has herbicidal activity against Cyperus rotundus weeds of chitosan were demonstrated. Conclusively, these natural by-products can be used as biocidal agents against different pathogens.