They are your employees, you have to pay worker's comp

If you hire a licensed company, they are bonded against damages caused to your house, and their employees are insured under worker's compensation system of your state.

If you hire a day labor, they are YOUR EMPLOYEE. Any damage caused to your house is not bonded, and their injury are not covered by worker's comp. So you as their employer are completely responsible.

You can try to get them some coverage as "social guest" under your home owner insurance, but it would bordering on lying to the insurance company that they are "guests", not "workers".

Your best bet is to consult your state's worker's comp law. Google it around, such as "day labor worker's comp (your state)".
e.g. http://www.contractortalk.com/f16/workers-compensation-day-laborers-95819/