If answers to all the following questions are Yes then the insect is a Mosquito. If the answers are No, then the insect is Not a mosquito. 

1. Does it have a long, needle-like mouthpart? (picture below) This part is called the proboscis that mosquitoes use to suck blood. 

2. Does it have a pair of wings? One on each side. 

3. Do the wings have scales?

Following are the insects that may be confused as mosquitoes. 

1. Cranefly

If the insect looks like a mosquito, but it is too big to be one then it is most likely a cranefly. Craneflies do not bite humans, therefore do not transmit any diseases. They feed on flower nectar. Craneflies do not have the needle-like mouthpart (proboscis) and the wings do not have scales. 

2. Midges

There are non-biting (Chironomidae) and biting (Ceratopogonidae) midges. The biting midges are commonly known as "no-see-ums." Compared to mosquitoes, midges are extremely small. Non-biting midges can grow up to half an inch, however, biting midges are often about one-eighth of an inch. Midges do not have a needle-like proboscis, but the biting midges have mouthparts that can cut through human skin. Midges also lack scales on their wings. Midges are found in swarms and can be extremely annoying, but they are not known to transmit any human diseases in the US.