What to look at:

LEGS
Insects: 6
Spiders: 8

MEALS
Insects: a wide variety — some even eat plastic, paper, and lint
Spiders: mostly insects, but some even eat small frogs or mice

ANTENNAE (an-TEH-nee)
Insects: yes — that's how they smell
Spiders: no — they sense through bristles on their legs

WINGS
Insects: usually
Spiders: never

BODY SECTIONS
Insects: 3: head, thorax, abdomen
Spiders: 2: cephalothorax (seh-fuh-luh-THOR-ax), abdomen

Information adapted from Science World.