Complex sentence: While a sting from this scorpion is extraordinarily painful, it normally would not kill a healthy adult human; young children, the elderly, or infirm (such as those with a heart condition and those who are allergic) are at much greater risk.
Split into simpler sentences: While a sting from this scorpion is extraordinarily painful, it normally would not kill a healthy adult human. However, young children, the elderly, or infirm (such as those with a heart condition and those who are allergic) are at much greater risk.