Here's why:

* Arthropoda is a massive phylum that includes all invertebrates with jointed legs, a hard exoskeleton, and a segmented body.

* Lice are small, wingless insects with a segmented body, six legs, and a hard exoskeleton. They fit the definition of arthropods perfectly.

So, while lice are insects, they are also a part of the larger group of Arthropoda.