These are actually called Crane flies, and while they look like scarier and meaner (and obviously bigger) mosquitoes, they’re actually quite harmless.
They look very similar to mosquitoes (maybe a cross between mosquitoes and spiders), but are significantly larger growing up to 60 mm in size with some tropical species growing up to 100 mm. They have very long thin legs and slim abdomens. Female Crane flies have slightly larger abdomens that end in a pointed ovipositor that mimics the look of a stinger (but they can’t actually sting).
When not moving, the wings are held out from the body, and unlike mosquitoes they are actually quite ungraceful fliers and may appear to wobble through the air at times. Another key difference between the two is that they’re attracted to light – that’s mainly the reason why they hang out in and around your homes, and not because they’re drawn to your blood.
Unlike mosquitoes, they don’t bite people or animals. They also aren’t known to carry any disease they can spread to people and animals. They may occasionally eat nectar, but in most species the adult does not eat at all. An adult crane fly only lives for about 15 days, and spends its time finding a mate and laying eggs before it dies.
Most of its life is spent as a larva, and they’re commonly referred to as leatherjackets or leatherjacket slugs due to the way they move and eat roots. These are soil-dwelling larvae, and they’re more numerous after a wet autumn. They mainly eat lawn grass but may also end up damaging small plants in flower beds and vegetable plots as they chew their way through.
One way to tell if you have an infestation of leatherjacket slugs is if you notice brown or dead patches of grass. You can look through the soil and you should find those slugs at the surface or near the surface. They typically remain under the soil, but will come up the surface on wet nights to feed on plant stems. They have elongated, tubular bodies up to 30 mm in length and are grayish brown.
They may be beneficial to gardeners as they speed up progress in a compost pile by feeding on decaying organic matter, however may end up killing your plants if there are too many feeding on them.
If you have an infestation, you can use parasitic nematodes (SteinernemaFeltiae) on your lawn or soil. These nematodes enter the bodies of leatherjacket slugs and infect them. However, they need a minimum temperature to exist –54°F (12°C)– so it may be tricky to use them. You can also introduce natural predators such as birds. You can encourage insect-eating birds on your property by hanging nest boxes and bird feeders on your property. If you have leatherjacket slugs, rest assured these birds will come find them.