Hi there Will.
How old exactly is your little brother? Is there any strong family history of skin cancer?
Dermatology is a very visual line & as such, it is best to get a clear digital photograph of the lesion & upload it on this site using the upload data icon.
Alternatively, better to see a dermatologist
@ ground 0 for best results as this may require a skin biopsy
to decide one way or the other.
Based on your history alone, it is impossible to say if this is related to some sort of spider related injury
& lesion therof.
Best of luck & hope it all pans out well..cheers!
Dr Praveen Rodrigues MD