Rain or shine, spin and dine: unravelling how weather shapes spider food webs (and silk webs)
Submitted by editor on 22 June 2023.
Figure 1: A spider on a dew-laden web, eating a parasitoid wasp.
By Jordan Cuff
Do you crave a nice cool ice cream on a hot day? Have you ever looked out on a dreary downpour and craved your favourite comfort food? You aren’t alone if you change what you eat with the weather! In our new article in Ecography, we show that spider diets change over time and depending on weather conditions. This does reflect changes in the prey available to them to some extent, but not perfectly – they also change the structure of their webs and their prey preferences!
To investigate the relationship between spider diets and weather, we used data from two previous studies based in cereal crops near Cardiff, Wales: one focused on biocontrol of crop pests and the other on how crop harvest changes what spiders eat. For these, we found out what spiders were eating by sequencing the DNA from prey in their guts using DNA metabarcoding, and compared this against the prey available to them which we collected via suction sampling. By combining these datasets (alongside measurements of the spiders’ webs) with weather data from a nearby weather station, we were able to investigate how weather affected the foraging ecology of these spiders.
South Wales is well-known as a rainy region of the UK, but weather conditions vary massively throughout the growth period of cereal crops, presenting a range of obstacles and opportunities for foraging invertebrates. During the height of summer, for example, the ground dries and cracks, creating fissures into which many invertebrates retreat. When we were collecting these spiders, we saw them capitalise on this opportunity to snack on prey also seeking refuge from the sun by building webs across these crevices. This is just one example of weather directly affecting the foraging behaviour of invertebrate predators (there are many other examples discussed at length in the paper)!
Figure 2: A spider snacking on a thrips under its web, which it has built across a fissure in the ground.
We show in our paper that the diet of spiders changes over time, weather gradients and interactions between different weather variables and time. Many of these changes showed quite complex trends and patterns, whereas others were relatively linear. At the same time, however, the prey communities available to the spiders also changed as a result of weather and time. Were spiders just eating different things because the buffet that they were attending was changing its options?
We clustered samples based on weather conditions and simulated spider diets for different weather conditions in prey choice null network models. This showed us that spiders weren’t just eating what was available, and that their selectivity/preferences changed under different conditions! Under wet and low dewpoint, high pressure, and dry and windy conditions, spiders consumed a greater number of prey than we would expect based on what's available to them.
Figure 3: A bipartite network figure from the paper which shows that prey preferences differ between spiders under different weather conditions.
Can we use these weather-dependent prey choice data to guide inter-annual predictions of trophic interactions using null models? Perhaps to some extent, but we show that weather alone is an insufficient predictor. We need to build more data-rich models accounting for a greater diversity of drivers of trophic interactions to represent better the complexity of these networks. We give some examples of the likely mechanisms driving the differences in spider foraging ecology and prey community structure related to weather, but these complex systems need further study to understand fully the impacts of weather and, even more urgently, climate change.
Do check out the full paper for all of the details!