Viruses are weird – they are non-living, yet still contain genetic information and are dependent on a live host to actually replicate and survive. Unlike many other parasites, since viruses are basically just a string of DNA or RNA, they actually need to actually get inside the cells of their host and hijack some of the components of these cells to allow them to replicate. After infection they are (at least partially) in the driving seat and can control and manipulate how some cells behave.
This means that viruses often have the capacity to also alter the behaviour of their host – which can be particularly beneficial to help ensure that the virus can also spread from one host to another. A good example is rabies, whereby the virus triggers infected individuals to become exceptionally aggressive – a surefire way to probably lead to them biting another individual and allowing infection to occur via the bite wound.
Sometimes the behavioural changes can be more nuanced – in this case caterpillars infected by a baculovirus start perceiving then sun in a positive light (pun definitely intended). Infected caterpillars become attracted to sunlight and feel compelled to move towards it (this process is known as phototaxis). Unfortunately in this case is is drawing them to an untimely death. Having the caterpillars die near the tree canopy is beneficial for the virus, as its a better scouting ground for newer hosts.
Tanya Strydom is a PhD candidate at the Université de Montréal, mostly focusing on how we can use machine learning and artificial intelligence in ecology. Current research interests include (but are not limited to) predicting ecological networks, the role species traits and scale in ecological networks, general computer (and maths) geekiness, and a (seemingly) ever growing list of side projects. Tweets (sometimes related to actual science) can be found @TanyaS_08.