If you have been outside at all over the past couple weeks, you have probably noticed a large swarm of black and red coloured insects.
These are called Boxelder Bugs or Maple Bugs. These bugs are harmless to humans but can become a nuisance when they invade areas in large numbers.
According to Wikipedia, they are found on boxelder, maple and ash trees. They are strong smelling and use that odour to discourage predators such as birds and spiders. Maple Bugs overwinter in plant debris or protected human-inhabited spaces.
The reason you may be seeing the large numbers is that they like to sun themselves and cluster together in large groups to stay warm in the Autumn.
The removal of boxelder trees and maple trees can help control boxelder bug populations