Skip to Content

As the Worm Turns

Speciation and the Apple Maggot Fly

Martin Kelly
Department of Mathematics & Natural Sciences
D'Youville College


At what point in evolutionary development does a group of individuals become two distinct species? This case addresses that fundamental question by asking students to decide whether apple maggot flies are distinct as a species from hawthorn maggot flies. In making their decision, students examine the different models of speciation and consider the primary forces that effect evolutionary change. Developed for an advanced undergraduate course in evolutionary biology, it would be appropriate for any biology course in which students are taught about the models of speciation. It could also be used in a general ecology course in which students consider the distribution and use of resources leading to niche specialization or in a genetics course if restrictions in gene flow are taught in the context of speciation.


  • Define evolution in the context of population genetics.
  • Explain each of the five forces that cause evolutionary change.
  • Describe three ways in which species can be characterized and clearly differentiated.
  • Understand that speciation as a process is based on the same forces of evolution.
  • Distinguish between allopatric, sympatric, and parapatric speciation.


Biological species concept; phylogenetic species concept; morphological species concept; population genetics; Rhagoletis pomonella; allopatric; sympatric; parapatric; natural selection; mate choice; genetic drift; gene flow; insect; evolution

Educational Level

High school, Undergraduate lower division, Undergraduate upper division



Type Methods




Subject Headings

Evolutionary Biology Ecology Genetics / Heredity

Date Posted


Teaching Notes

Case teaching notes are password-protected and access to them is limited to paid subscribed instructors. To become a paid subscriber, begin the process by registering.

Teaching notes are intended to help teachers select and adopt a case. They typically include a summary of the case, teaching objectives, information about the intended audience, details about how the case may be taught, and a list of references and resources.