I like to gather butterflies for my collection, I am an Entomologist.
oh, you collect and study insects. This would be a branch of zoology.
What other branches are there?
I'm not sure but historically  the definition of entomology included the study of terrestrial animals in other arthropod groups or other phyla, such as arachnids, myriapods, earthworms, land snails, and slugs.
I am not a big fan of arachnids or any type. 
Me neither. Entomology alsooverlaps with a cross-section of topics as diverse as molecular genetics, behavior, biomechanics, biochemistry, systematics, physiology, developmental biology, ecology, morphology, and paleontology.
I didn't realize Entomology helped with so many different areas. What is the most popular field?
Not sure about that but paleontology would be my favorite.At 1.3 million described species insects account for more than two-thirds of all known organisms, date back some 400 million years, and have many kinds of interactions with humans and other forms of life on earth.