How to sex Drosophila melanogaster

One of the most basic and critical tasks in Drosophila research is separating male flies from females, and picking virgin females to set up genetic crosses. Not recognizing the differences between the sexes can lead to ruined experiments and bad times! Here I show you how to sex Drosophila melanogaster AND find those precious virgin females.

Males vs. Females: It’s simple

To sex Drosophila melanogaster (i.e. differentiate males from females) is actually very easy:1

  • Drosophila males have shorter, more pointed abdomens with a concentrated black patch at the tip. Females have longer, more rounded abdomens.
  • Drosophila males have distinctive bristles on their forelegs called sex combs.

Virgin females are critical

A Drosophila melanogaster female can store sperm from multiple rounds of mating, and use those sperm to fertilize her eggs over the course of days to weeks. Therefore, when setting up a genetic cross between two different fly strains, it is essential to first retrieve and separate virgin females from their sibling males to ensure that no undesired mating and fertilization occurs.

How to pick virgin females

After eclosing (i.e. hatching from the pupal stage), an adult female will be unable to mate for a critical window of 8 to 10 hours. These virgin females are also visually distinct: they are typically larger and lighter-colored than older females, and will usually have a dark green spot on the underside of their abdomen called the meconium (the remains of the last meal the fly consumed before pupating).2

Drosophila melanogaster virgin female
A virgin female. Here you can see the dark green meconium at the tip of the abdomen, but it may not always be so distinct. Image source: Searching for Virgin Female Flies Part 2.
Drosophila melanogaster virgin female
A different view of the male’s (left) and female’s (right) meconium. Image source: Distinguish Virgin Drosophila.

With virgin females, your genetic crosses will run smoothly

Drosophila melanogaster mating
The act of sweet fly lovemaking. Image source: Newsweek.

If you enjoyed this guide on how to sex Drosophila melanogaster and identify virgin females, please check out my post on how Drosophila melanogaster genes are named.


  1. WikiHow: How to Distinguish Between Male and Female Fruit Flies. Available at:
  2. Pulver SR and Berni J. The Fundamentals of Flying: Simple and Inexpensive Strategies for Employing Drosophila Genetics in Neuroscience Teaching Laboratories. J Undergrad Neurosci Educ. 2012 Fall; 11(1): A139-A148. PMID: 23493248

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