Seeing blue: do jumping spiders select their food based on colour?
Jumping spiders are remarkable animals, in part for their 'cute and fuzzy' factor (they are among the most charming and adorable of all the spiders!), and because of their incredible eyesight. They see further and better than most of their spider cousins, and have among the best eyesight of all the arthropods. They use this remarkable vision when selecting their food, as reported in a fascinating paper by Lisa Taylor and her colleagues.
In a laboratory setting, field-caught jumping spiders (Habronattus pyrrithrix) will select blue-coloured crickets, and avoid red/yellow ones. If those field-caught spiders are re-tested after a few weeks, they lose some of that selectivity, but the trend still holds up: they prefer the blue-coloured crickets. Naïve, lab-reared jumping spiders also select blue-coloured pretty over the red / yellow crickets. Taylor et al. argue that one of the reasons they probably avoid the red and yellow prey is because of aposematic coloration. In natural systems, these colours typically represent prey that have chemical defences and they advertise their toxicity to their predators by being bright and bold in coloration. Red or yellow means unpalatable food. (Clearly not the case for humans!)
Taylor et al. did their research by collecting Habronattus pyrrithrix in the field, keeping them alive in the laboratory by feeding them non-coloured prey, but then placing the spiders in an arena where they could first view different coloured crickets, and after released, the jumpers could move into the arena and select different crickets. They repeated these methods using naïve (laboratory-reared spiders) which had no prior experience with palatable or unpalatable prey. Taylor et al. coloured the crickets by adding food dye to the water of newly hatched crickets and as they drank the water, their body changed colour (this is a very nifty method!)
The avoidance of red/yellow combined with the selection for the blue prey is an amazing and fascinating result, in part because it suggests these jumping spiders have some innate capacity to avoid red/yellow prey, since this food selection occurred with naïve spiders that had not previously been exposed to range of prey colours (i.e., in the field they are exposed to many different prey types, and thus can 'learn' foods to avoid). However, they had very strong results with field caught spiders, and those spiders lost a little bit of their selective ability over time, which also suggests that colour choice has some flexible and needs reinforcement. To quote Talyor et al. "the results suggest that colour is a salient feature of prey for these spiders and that these biases, while flexible, appear to originate from a pre-existing innate preference template". Stated another way, they dislike red and yellow food because of some genetic underpinnings, but this selection is relatively plastic and reinforcement is important.
So, why did the jumping spiders select blue food? To me, this is among the most surprising result, as I certainly wouldn't have predicated any selection for blue. Taylor et al. discuss that although blue is a common colour for potential prey of jumping spiders (e.g., some Lepidopterans, caterpillars, damselflies), these prey were rare in their study area. In fact, the only potential blue prey was a rarely observed chrysomelid beetle. The authors suggest that 'novelty in prey choice' may be the mechanism. The fact that these curious spiders seldom encounter blue prey may lead them to check it out under the laboratory conditions, and therefore that particular result may be due to taste-testing.
In sum, this was a fascinating paper: jumping spiders are tiny little animals with small brains yet an incredibly sophisticated visual system, and one that clearly plays a role in selecting food. The generality that spiders should avoid red and yellow-coloured food is a strong signal, and adds to a broad literature on aposematic coloration in nature. I think the most unique finding in this paper (in addition to the awesome methods!) is that the naïve spiders spiders also show colour biases: without experience of palatable/unpalatable prey, the signal to avoid certain prey type based on coloration is strong.
Taylor, L., Maier, E., Byrne, K., Amin, Z., & Morehouse, N. (2014). Colour use by tiny predators: jumping spiders show colour biases during foraging Animal Behaviour, 90, 149-157 DOI: 10.1016/j.anbehav.2014.01.025