A scientist who studies fleas (or insects in general) is a zoologist who is specifically an entomologist.
A scientist that studies insects, including fleas, is an entomologist.
Entomologist.
An acarologist is a person who studies ticks and mites.
The Person Who studies about mamals , he is called mamalogist....
A person who studies volcanoes is called a volcanologist.
A person who studies the grass and soil, etc. is called a Agrostologist
A person who studies geology is a geologist.
A person who studies bees is called an apiologist.
a person that studies gems is called a gemologist.
A person who studies audiology would be called an audiologist.
A person who studies water and its properties is called a Hydrogeologist.
A person that studies animals is called a Zoologist.
A person who studies birds is called an ornithologist.
A person who studies the grass and soil, etc. is called a Agrostologist