Hey I found it for you!It would be Cuterebra Spp.
Common name: Rodent Bot Fly
It infests dogs and cats. Larvae infest rodents companion animals and occasionally humans. It acts as an irritant, some migrations can be fatal.
The larvae only infests mammals, the eggs, pupae and adult flies are part of the environment.
Does it look like a lump in the skin with a breating hole? The larvae will be dark red with spines.
You should take your dog to the vet if you think he has this as the larvae will need to be extracted and he may need antibiotics. They dont come out specifically on the neck it can be anywhere.
Hope that helps!!
If you have a pic I would love it if you emailed it to me I would love to see it as I am studying parisitology right now and i have never seen it here!!!
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Cheers
Masako