Many nematode species, including our favourite C. elegans, are self-fertilising hermaphrodites. This essentially means that they are females that are able to produce their own sperm. Selfing (as it is sometimes called) might seem a strange way of reproducing, but it can have advantages: for example, even a single worm may be able to successfully invade a new environment and produce many offspring.
For scientists like me that are interested in behavioural genetics, it makes it possible to study some mutations that it would not be possible to propagate in animals that couldn’t self. Take unc-7 mutants. As you can see in this video, worms with mutations in their unc-7 gene are not able to move normally.
That’s why they’re called “unc,” which stands for uncoordinated. The unc-7 gene makes a protein that connects neurons together and when it’s broken or absent, the neurons don’t communicate properly and that leads to abnormal motion.
If we had to rely on males to find and fertilise females, these mutants would be difficult to raise, but because they can reproduce by selfing, even severely uncoordinated worms can often survive perfectly well in the lab. That means we can study their behaviour (including egg laying!) and learn about how genes that lead to uncoordination work.