The insect injects toxin into the skin. The toxin spreads and is carried by the circulatory system of the human body. The toxin robs the blood of its ability to carry oxygen. The muscles sense this and react by tightening.
If the insect toxin is a nerve toxin, there should be numbness in the extremities and then tightening of the muscles.
The insect toxin may also solicit an autoimmune response and that would bring on arthritic-like stiffness and pain.
Usually by the time muscle tightening is felt, the insect’s toxin would have already invaded the muscles and the blood stream. It then depends on whether the location of the insect bite is still itching, if there is localized redness and swelling, if there is any blister, if there is any white pus, bleeding, etc. Wash and scrub the bite with heavy soap, vinegar, alcohol, iodine, to get rid of the residual toxin at the bite mark. Boost the immune system with garlic and ginger. Detox teas like jasmine and chrysanthemum might also help. If there is persistent numbness and stiffening of the muscles for more than a day or two, go to see the doctor immediately.
Insect bites may be more devastating to a person with a compromised immune system due to prescription medications than to a normal healthy person not taking any immune suppressant type of prescription medication.