DNA isolation Strongyloides stercoralis

I am working about Strongyloides stercoralis and T canis. I have a problem whem I make isolation dna When a finished the complete protocols (After lysis buffer , proteinase K treatment and Phenol, chloroform and precipitation with ethanol) when I make the gel I do not have DNA bands, but when I measure in espectofotometro I have few micrograms with suitable purities. I want to know whichever L3 larvae is necessary for a good extraction