The Spidey shadow is always a cool visual whenever it turns up.
Amazing Spider-Man (Vol. 1) #155
Published: c. January, 1976?
Cover Date: April, 1976
“Whodunit!”
Writer: Len Wein
Artist: Sal Buscema
Inker: Mike Esposito
Letterer: Irving Watanabe
Colorist: Glynis Wein
Actually the shadowy spider in that panel reminds me of the symbiote after it first escaped from the FF and was hunting Peter – it looked like a shadow then too.