These are almost 100% NOT spiders. It would have been much more helpful if you included a picture because so many people misidentify insects and arachnids that the could be a number of things. There are 0 spiders in the world that parasitize humans so you would never find them on sores on your body and especially not in groups. Spiders can cause sores if they bite you but that is a defense mechanism and they would attempt to flee soon after, they wouldn't hang around.

I can't be sure with the limited info provided but i think they are likely one of 3 things:

1. Some type of mites. Mites are close relatives of spiders and do look a lot like very tiny spiders because they have 2 main body segments. Also there are many types of mites that live on mammals including humans and can cause intense itching sores like this:

Google Image Result for https://i.pinimg.com/originals/fa/94/e3/fa94e3c8da405b134799453d2beecf27.jpg

Scabies is caused by mites and chiggers are also mites. These mites are so small that you can't see them with your naked eye though so it's unlikely these are the cause. It's very easily treated though, just need permethrin cream and they're gone in a couple days.

2. Lice. Lice are tiny insects that live on their host and feed off of their blood. The entire life cycle happens on the host and if untreated they can grow to large numbers on the body and they specifically live in areas with lots of hair. They're usually whitish but can be fairly dark in color like this:

Google Image Result for https://www.naturalremedies.org/images/head-lice-1.jpg

3. Bed bugs. Another common human blood feeding parasite. These tiny bugs usually are very good at hiding during the day and only coming out to feed on you at night so usually you don't see them unless you specifically try to find them. Here's what they look like:

Google Image Result for http://www.deadpestz.com/wp-content/uploads/2017/11/babybedbugs.jpg

Whichever it is, you should get them properly identified and treated before they become a huge problem. Capture some in a container and take them to someone who can identify them.

Good luck