I've seen on youtube people putting bandaids or vaseline over the bump (for botflys) and that pretty much suffocates the larvae and kills it and it pretty much falls out. . .but I don't think you can do that with a dog just because the dog would lick it off.
This does look suspiciously lke botfly to me. Although these can be removed at home, by far the safest thing to do is let the vet remove it (if it IS botfly) I have heard that improper removal can result in infection, and the botfly larva has "anchoring" barbs or tiny hooks on it which if you tried and failed, to remove it could cause a problem. I think taking these out is a bit of a knack, which the vet should be able to do easily, but might be tricky for someone who hasn't done it before.
How old is your dog? Does he have other health problems? Does the lesion seem to bother him (does he pick at it, act like he is in pain when you touch it?) Is there a lump or anything underneath it?
Since it does have the discharge I would take him to the vet. A veterinarian is the only one qualified to give you a legitimate medical answer. If it IS a botfly larvae you need to get him to the vet fairly quickly and don't try to remove it yourself. The larvae will continue to burrow and kill living tissue, which is not only extremely painful but can lead to infection.
*I am currently working towards my BSA in Animal Health Technology HOWEVER this is solely my opinion and all issues should be discussed with your veterinarian*
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