Can anyone identify this bug on my dog?

I recently got a new dog he is 3years and the previous owner said he had allergies so i contined the treatment she gave him but he was still ichting intensly and today i found two small crawlers on him that died with a simple squish and water but i cant seem to find anything explaining what i is . They can be seen with the naked eye and it is not a flie or tick it has a black head a torso a long torso and another black tip on the end Can anybody help?