Most of us can tell one insect order from another. In other words, you can tell the difference between a beetle and a butterfly, two very different groups. There are two insect groups, however, that are often confused, flies (the order Diptera) and wasps, bees, and ants (the order Hymenoptera). Even if you can recognize a yellowjacket and you know what a house fly looks like, when it comes to the lesser flies and the less obvious wasps, you may not be able to tell which group the insect belongs to. Because insects are such a large and diverse group, there are always exceptions to the rules, but here are some ways to tell a wasp from a fly.

1. Count the number of wings

The best way to identify a fly is by its wings. The order name “Diptera” means “two wings.” In flies, the hind pair of wings has been reduced to two small knobs, called halteres, which may not even be visible. Wasps, bees, and ants always have two pairs (or four total) of fully developed wings. You’ll have to look at a dead, or very still, specimen to see the second, slightly smaller pair of wings.

2. Is there a “wasp-waist”?

Most insects in the order hymenoptera have a constricted abdomen which some call a wasp-waist. The thorax is connected to the abdomen by what sometimes seems to be only a narrow thread. Bees are an exception, they don’t have the wasp-waist but they do have four wings. Flies do not have the narrowed wasp-waist at all.

3. Open wide! Check the mouth

This difference you may not be able to see, but if you think about what the insect is doing, it may make sense. Flies have sucking-type mouthparts, either piercing-sucking like mosquitoes or sponging-up mouthparts like house flies. Wasps and ants usually have chewing mouthparts and bees have a long, tongue-like mouth.

4. Is there a stinger at the rear?

One final difference is that female ants, wasps, and bees (Hymenoptera) have an ovipositor at the tip of the abdomen that is often modified into a stinger. In flies (Diptera), there is no stinger. So, here’s the easy way to tell a wasp from a fly — if it stings you, you know it wasn’t a fly!