How do schistosomes find and attach to human skin?
Schistosoma recognize human skin by mechanical, thermal and chemical stimuli from host. Attachment of parasite to skin is  stimulated by L-arginine. Schistosomes specifically bind  to L -argine by chemotaxis. L-arginine guides this parasite towards site of penetration. The lipids on the human skin surface also serve as signal for host invasion.

It is also reported that parasite may use L-arginine to synthesize nitric oxide for blood vessel dilation so that it can easily penetrate into the host. Schistosoma may attach to L-arginine of surrounding tissues to escape the cellular immune response from host. 

(Via: https://www.ncbi.nlm.nih.gov/pubmed/11860033)

These parasites enter the host through skin by producing several proteolytic enzymes to degarde the host tissue proteins including elastin, condromucoprotein, keratin, fibronectin, laminin and collagens.  

Two distant serine proteases are responsible for digesting host tissue. One is Chymotrypsin-like protease which degrades protein with large hydrophobic side chains. And the second one is Trypsin-like protease which prefers proteins with positively charged side chains. 

(Via: http://www.jbc.org/content/275/49/38667.full#ref-2)