Ditto is one of the most special Pokémon of all, his ability to convert to any other Pokémon has marked him since the first generation and Pokémon GO has been one of the "difficult characters", because you never know when or how who can show up.
This is because Ditto does not seem like him in wild meetings. Buses barely know that they caught a Ditto after catching Pokémon that they meet and that it will be Ditto again after the catch.
Ditto can now appear in Pokémon GO camouflaged in seven more Pokémon than before. These are: Weedle, Spinarak, Hoppip, Seedot, Skitty, Numel and Bidoof ; which adds Paras, Venonat, Hoothoot, Ledyba, Remoraid, Whismur and Gulpin, to complete fourteen possible camouflages for Ditto.
One of the special studies has the requirement to catch a Ditto to complete it, so those who continue to search for it now have several more options to get one.