Mice are a destructive and dangerous infestation. They need to chew constantly due to their ever-growing incisor teeth and this means they can rip apart portions of a house and even chew through concrete. One of the biggest dangers is that they chew on electrical wires and can start a fire. Having them in a shed, assuming it has lights or other electrical devices, means you could end up with a fire in the shed. There are many reasons mice will infest a shed instead of a house. Sheds often are not paid attention to unless there is something in them that you need. They can go years without being checked and in that time can become infested with rodents. If you use your shed regularly then that still does not stop them from entering but gives you the chance to catch an infestation in its earliest stages. For this reason always inspect your home, your garage and your shed for mouse feces. Knowing in advance could change the situation from a serious threat to a small infestation that can be treated quickly and easily. Trying domestic treatments first is ok but if you find that you have caused and killed or released multiple mice and they keep coming then a professional treatment may be the only way to go. Remember how quickly mice can reproduce. They will grow in population faster than you can catch them.
Keeping mice out of a shed is one thing. Treating the mice that are already in the shed is another. If the shed has already been infested then you will need to get rid of them while also dealing with the holes they have made to enter it. Treating mice domestically with poison or snap traps is often ineffective as they can multiply quickly. A single female mouse can give birth to up to ten babies in a single litter. Those babies can become adults in just two weeks, mate again, and produce even more mice. The population can grow rapidly and quickly become untreatable with snap traps and other domestic methods of catching or killing them. That is why a commercial treatment may be needed. Commercial treatments use commercial-grade bait in locked and tamper-proof bait stations which are safer, more effective and faster. This is because all the mice in the shed or house can eat the bait all at once. Unlike a snap trap which can catch one mouse and then needs to be reset, bait can be eaten by every mouse and kill them much faster. Once the infestation is dealt with you can focus on sealing off their entryways. These can be almost anything. An open plumbing vent is common in old houses that had to be updated, any opening used to add an electrical cord to the house. Weep vents in brick houses are mortarless holes between the bricks, mice can enter these as well. Foundation gaps and other areas that are open like wall vents make for easy access but the most common entryway they use may surprise you, it’s just a door that was left open.