Arachnology and the Science of Spiders

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Jessica Henneken with one of her St. Andrew's Cross Spiders - image courtesy of Jessica Henneken

‘Part of science more broadly is knowledge for the sake of knowledge, you don’t necessarily know that something’s going to have a huge impact on humanity or anything like that, sometimes it’s just about knowing a little bit more about the world that we live in’ – PHD Candidate Jessica Henneken.

PHD candidate, arachnologist and behavioral ecologist Jessica Henneken has been studying spiders and their silk while completing her doctorate at the University of Melbourne and has five peer-reviewed scientific papers published.  

She says that arachnology is both an interesting and useful science.

St. Andrew’s Cross Spider – image courtesy of Jessica Henneken

“Spiders are a really important group of predators and we know that they eat insects, so anything that eats insects is going to shape the vegetation of its environment because the insects will eat the plants, understanding how they [spiders] interact with their environment can give us a better idea of how to maybe control populations of pest species or how ecosystems work more broadly,” she says.  

The kind of spiders Ms. Henneken works with are called the St. Andrews’s Cross Spider, which she says are a ‘chilled-out’ type of spider and ‘have not be shown to be harmful to humans.’

In the lab Ms Henneken designs experiments to test the behavioral effect these chemicals have on other animals and prey species like insects.

“I use spiders as a study system to ask questions about animal behavior and how behavior is influenced by the environment, and I’ve been studying the chemicals on spider silk that they use to communicate with one another, and also how they use them to communicate with prey and predators,” Ms Henneken says.

St. Andrew’s Cross Spider – image sourced from Pixabay

During her experiments, which she compares to detective work, Ms Henneken has made some surprising and fascinating discoveries.

“One of the chemicals that we found in the spider silk was a chemical called putrescine, putrescine is really stinky, it’s produced if something is rotten or decomposing, like if an animal had died the bacteria would eventually produce putrescine,” she says. “Lots of insects feed on dying animals and what I found was that the putrescine on spider silk is attractive to insects, so spiders that add putrescine to their web are going to catch more prey and then that’s going to have fitness benefits so they might be better fed and if you’re better fed you might produce more offspring.”

St. Andrew’s Cross Spider – image courtesy of Jessica Henneken

In one of her papers Ms Henneken explores how diet shapes pheromone expressions. She defines pheromones as “chemicals produced by animal that lead to a behavioral response in another animal of the species”.

“Spiders produce pheromones that travel through air that attract males to their location, so females produce pheromones from their body [and] it travels through the air and males searching for that female will detect it and then they are able to find the female that way,” she says.

The pheromones Ms Henneken studied are called mate assessment pheromones, she says that “these allow individual spiders to assess the female based on her quality as a reproductive partner” and “for a male to tell the difference between one female or another, their pheromone profile has to differ”.

According to Ms Henneken the ability to assess a female’s reproductive quality is extremely important because male St. Andrew’s Cross Spiders often die after mating because they are eaten by the female, and they need to make sure they are getting the best possible outcome from this singular mating opportunity.

“I looked at females given different diets and how that changed the expression of pheromones in her silk and how that changed the chemicals produced and in what amounts, and then I looked at males who were given different diets and how they responded to the differences in those pheromones,” she says.

St. Andrew’s Cross Spider – image courtesy of Jessica Henneken

After some early feelings of fear and avoiding directly touching her spiders, Ms Henneken says she quickly became comfortable handling them after working with them for some time.

“If you can get past your initial creepy-crawly, icky feelings they’re actually really pretty,” she says. “They are very unlikely to bite you unless you go after them and prod them with your finger, they’re surprisingly mellow and are happy to just sit in their web in this Zen state.” 

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