Although both males and females posses venom, only females have fangs long enough to inject it. This neurotoxic venom works in the synaptic area between nerve cells. Essentially, the venom causes massive neurotransmitter release from the cells, most notably discharging large amounts of acetylcholine, norepinephrine and dopamine. Eventually, all of the neurotransmitters become depleted from the neurons, causing another set of problems.
Symptoms can start within an hour of the bite, and the initial manifestations depend on where the victim was bitten. The acetylcholine release causes spasm of muscle. With a lower extremity bite, this can lead to abdominal cramping, and lower extremity spasm. Bites in the arm tend to cause facial cramping, and chest pain associated with muscle spasms there.
Norepinephrine and dopamine release can cause shortness of breath, high blood pressure, and fast heart rate.
As symptoms progress, and the neurotransmitters are depleted from the neurons (in 2-8 hours), paralysis can set in, perhaps starting with a facial droop, and even progressing to respiratory arrest, as the victim us unable to use the muscles to breathe. Cardiac arrhythmias can also be present at this stage. The total course can last two or three days.
As the initial stages are very painful, patients may require IV narcotics for pain, and benzodiazepines (Valium-like drugs) for cramping. Late stages may require mechanical ventilation in severe cases.
There is a horse serum based antivenin called Lyovac that can be infused IV over 2 hours. This drug is dangerous in it's own right, potentially causing seizures, for example. It has a mixed history of success, and may not work in children at all.
Generally, patients should be observed for some time following a possible bite, and some may need an ICU admission for further observation or care.
'Critter' bites are covered in AHA's First Aid course.